Today's Message Index:
----------------------
1. 03:14 AM - Re: Yak-List Digest: 4 Msgs - 12/07/20 (Craig Payne)
2. 03:56 AM - Re: Re: Yak-List Digest: 4 Msgs - 12/07/20 (Mark Pennington)
3. 11:21 AM - Re: Re: Yak-List Digest: 4 Msgs - 12/07/20 (Walter Lannon)
4. 11:58 AM - Re: Re: Yak-List Digest: 4 Msgs - 12/07/20 (Hank Gibson)
5. 01:23 PM - Re: Re: Yak-List Digest: 4 Msgs - 12/07/20 (Mark Pennington)
6. 02:20 PM - Re: Re: Yak-List Digest: 4 Msgs - 12/07/20 (Larry Pine)
7. 08:07 PM - Re: Re: Yak-List Digest: 4 Msgs - 12/07/20 (Walter Lannon)
8. 11:44 PM - Re: 18T Brake Shoes - image (RobertGreen)
Message 1
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
Some years back the popular fix was to file some notches in the flapper
valves. To me that seemed to defeat the purpose. Using a little MMO in the
fuel made me feel better anyway.
Craig Payne
On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server <
yak-list@matronics.com> wrote:
> *
>
> =================================================
> Online Versions of Today's List Digest Archive
> =================================================
>
> Today's complete Yak-List Digest can also be found in either of the
> two Web Links listed below. The .html file includes the Digest formatted
> in HTML for viewing with a web browser and features Hyperlinked Indexes
> and Message Navigation. The .txt file includes the plain ASCII version
> of the Yak-List Digest and can be viewed with a generic text editor
> such as Notepad or with a web browser.
>
> HTML Version:
>
>
> http://www.matronics.com/digest/digestview.php?Style=82701&View=html&Chapter 20-12-07&Archive=Yak
>
> Text Version:
>
>
> http://www.matronics.com/digest/digestview.php?Style=82701&View=txt&Chapter 20-12-07&Archive=Yak
>
>
> ===============================================
> EMail Version of Today's List Digest Archive
> ===============================================
>
>
> ----------------------------------------------------------
> Yak-List Digest Archive
> ---
> Total Messages Posted Mon 12/07/20: 4
> ----------------------------------------------------------
>
>
> Today's Message Index:
> ----------------------
>
> 1. 10:24 AM - Fw: CJ6 uneven fuel flow (Walter Lannon)
> 2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow (JON BLAKE)
> 3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow (Larry Pine)
> 4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow (Walter Lannon)
>
>
> ________________________________ Message 1
> _____________________________________
>
>
> Time: 10:24:05 AM PST US
> From: "Walter Lannon" <wlannon@shaw.ca>
> Subject: Yak-List: Fw: CJ6 uneven fuel flow
>
>
> From: Walter Lannon
> Sent: Sunday, December 06, 2020 9:09 PM
> Subject: CJ6 uneven fuel flow
>
> Currently there is a lot of interest in the above subject on the Red
> Star site. Since I have some experience in this area I thought I should
> respond but since it will be a rather long diatribe I thought the Yak
> List might be a better venue.
>
> My aircraft is a 1966 model CJ6a, one of four I imported from China in
> 1993. Did not start my own restoration until after selling my Harvard 4
> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
> including the fuel system where I found some questionable design
> features. During this period (from 1993) I also licensed a few others
> and found it was necessary to do a hot soap and water flush of the fuel
> vent system to remove bug debris.
>
> Many people have noted the fuel feeds from the LH tank first. That is
> not surprising since the LH vent system is much shorter than the RH and
> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
> tubing is internally clean and totally free of any damage that could
> restrict air flow. This is critical! There is also some minor effect
> favoring LH flow via the shorter fuel feed line to the header tank.
>
> The major design problem rests with the header tank flapper valves.
> There are three of these valves in the aircraft. One is in the fuel
> line from the header tank to the fuel pump. It=99s sole purpose
> is to direct fuel
> from the emerg. (wobble) pump to the engine fuel pump while preventing
> reverse flow back to the header tank. This is the type of function the
> valve is designed for and it works perfectly because there is a
> distinct difference in pressure on each side.
>
> With reference to the attached photos note the diameter of the flapper
> as compared to the diameter of the incoming fuel hole. A true
> =9Cflapper=9D valve is meant to open (or close) with fuel
> flow but pressure, though relatively small, is a factor. If we start
> with equal fuel one flapper will open (probably the LH). In theory as
> the pressure from the LH tank and the header tank is reduced at some
> point the RH will open and the cycle will repeat.
> But, in fact, the LH plus the header tank fuel is actually applying a
> force to the valve surface roughly double that of the smaller surface
> impacted by the RH fuel.
>
> I did some rough math based on tank volume and pressures, etc. and came
> to the following conclusion: - The major reason this system sort of
> works is called turbulence! If you could take off, climb and fly a trip
> with never a bump of any kind you will be out of gas with a full RH
> tank.
>
> As you probably noted I have modified the valves to allow closing
> pressure to impact some of the opening surface. My typical fuel
> imbalance is less than 5 lts. For me this is a hand filing operation
> (though a CNC genius could probably do it). You MUST retain a seating
> ring of the original closing surface. If you change that it will never
> close properly again due to the geometry.
>
> One of the un modified valve photos shows a Chinese character on a
> wrench flat. In English this reads =9CHINGE=9D and must be
> at the top. Improper positioning could well be the cause of serious
> imbalance.
>
>
> Cheers;
> Walt
>
>
> ________________________________ Message 2
> _____________________________________
>
>
> Time: 12:28:05 PM PST US
> From: JON BLAKE <saber369@comcast.net>
> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>
> Good info Walt... many thanks.
>
> When I first bought my CJ 15 years ago, I was told to wrap the vent on the
> belly with a fine mesh screen to keep the bugs out. I was also told that t
> he vents going out to each wing tips were installed by Yakity Yaks to help
> prevent a bug or other debris from causing fuel starvation. Is that true?
> Can you shed any more light on those vents?
>
>
> Jon Blake
> Saber369@comcast.net
>
> > On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
> >
> >
> >
> >
> > From: Walter Lannon mailto:wlannon@shaw.ca
> > Sent: Sunday, December 06, 2020 9:09 PM
> > To: yaklist@matronics.com mailto:yaklist@matronics.com
> > Subject: CJ6 uneven fuel flow
> >
> > Currently there is a lot of interest in the above subject on the Red
> Star site. Since I have some experience in this area I thought I should re
> spond but since it will be a rather long diatribe I thought the Yak List mi
> ght be a better venue.
> >
> > My aircraft is a 1966 model CJ6a, one of four I imported from China i
> n 1993. Did not start my own restoration until after selling my Harvard 4
> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration in
> cluding the fuel system where I found some questionable design features. D
> uring this period (from 1993) I also licensed a few others and found it was
> necessary to do a hot soap and water flush of the fuel vent system to remo
> ve bug debris.
> >
> > Many people have noted the fuel feeds from the LH tank first. That i
> s not surprising since the LH vent system is much shorter than the RH and
> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
> > tubing is internally clean and totally free of any damage that could
> restrict air flow. This is critical! There is also some minor effect favor
> ing LH flow via the shorter fuel feed line to the header tank.
> >
> > The major design problem rests with the header tank flapper valves.
> There are three of these valves in the aircraft. One is in the fuel line f
> rom the header tank to the fuel pump. It=99s sole purpose is to dire
> ct fuel
> > from the emerg. (wobble) pump to the engine fuel pump while preventin
> g reverse flow back to the header tank. This is the type of function the v
> alve is designed for and it works perfectly because there is a
> > distinct difference in pressure on each side.
> >
> > With reference to the attached photos note the diameter of the flappe
> r as compared to the diameter of the incoming fuel hole. A true =9Cf
> lapper=9D valve is meant to open (or close) with fuel flow but pressu
> re, though relatively small, is a factor. If we start with equal fuel one
> flapper will open (probably the LH). In theory as the pressure from the L
> H tank and the header tank is reduced at some point the RH will open and th
> e cycle will repeat.
> > But, in fact, the LH plus the header tank fuel is actually applying a
> force to the valve surface roughly double that of the smaller surface impa
> cted by the RH fuel.
> >
> > I did some rough math based on tank volume and pressures, etc. and ca
> me to the following conclusion: - The major reason this system sort of work
> s is called turbulence! If you could take off, climb and fly a trip with n
> ever a bump of any kind you will be out of gas with a full RH tank.
> >
> > As you probably noted I have modified the valves to allow closing pre
> ssure to impact some of the opening surface. My typical fuel imbalance is
> less than 5 lts. For me this is a hand filing operation (though a CNC geni
> us could probably do it). You MUST retain a seating ring of the original
> closing surface. If you change that it will never close properly again due
> to the geometry.
> >
> > One of the un modified valve photos shows a Chinese character on a wr
> ench flat. In English this reads =9CHINGE=9D and must be at th
> e top. Improper positioning could well be the cause of serious imbalance.
> >
> >
> > Cheers;
> > Walt
> >
> >
> >
> >
> >
> >
>
> ________________________________ Message 3
> _____________________________________
>
>
> Time: 01:30:00 PM PST US
> From: Larry Pine <threein60@yahoo.com>
> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>
>
> Great write-up on this. Let me add a little learned knowledge to this discu
> ssion. I have no issues with what Walt stated but a few years ago I had fue
> l starvation while on the ground. I could start the engine on my electrical
> boost pump but the minute I shut it off, the engine would die. I checked f
> uel levels, I removed and cleaned the fuel strainer and checked for flow, s
> till nothing. Only when I removed the flapper valve under the floor, the on
> e that feeds the wobble pump, I found the hinge in this flapper was worn an
> d could rotate to a place where it would get stuck closed. This was the fir
> st I have ever hear of this happening. I cleaned and lightly refaced both t
> he flapper and flapper seat. I then replaced the worn hinge pivot rod with
> a new brass one. I have plans to take apart this valve again during this mo
> nths annual and see if these is any wear taking place on the hinge rod. Luc
> ky I found this on the ground but confident had this happened in flight, my
> electric driven pump would have supplied enough fuel to get me back safely
> . Still some thing that should be examined.
>
> I have bladder tanks so my vents are extended to their respective wing tips
> with a separate vent for the header tank. I find that I tend to fly more p
> ressure on my left rudder because my knee board is on my right and lifting
> my right knee a little makes writing easier. This tends to cause a noticeab
> le fuel difference over a 2 hour period. I know, bad pilot bad. Very early
> on before I had my bladder tanks installed, I had to do an emergency divert
> because my one tank was almost dry and the opposite tank wasn't moving the
> needle yet. Only after landing I noticed the needle move. Constant fuel ma
> nagement has become the norm. I optioned to not install the vent shut off v
> alues after and incident I had with another RPAer. This pilot closed one of
> his vents to overcome the fuel flow difference and forgot to open the vent
> again. On roll out with the engine pulled to ideal, the engine died on the
> runway. It would start but than die again. When we got it to parking, we n
> oticed one bladder tank was sucked flat and dry..... The same side with the
> closed vent. Human factors are human factors! Unless you design a system t
> o incorporate some warning when the pressure builds or the vent is closed i
> ndication, this only complicates memory items that needs to be attended and
> eventually can lead to failures.
>
> Larry Pine On Monday, December 7, 2020, 10:48:19 AM PST, Walter Lannon
> <wlannon@shaw.ca> wrote:
>
> =C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020 9:09 PMTo:
> yaklist@matronics.com Subject: CJ6 uneven fuel flow=C2-Currently there i
> s a lot of interest in the above subject on the Red Star site.=C2- Since
> I have some experience in this area I thought I should respond but since it
> will be a rather long diatribe I thought the Yak List might be a better ve
> nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported from Chi
> na in 1993.=C2- Did not start my own restoration until after selling my H
> arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 100%
> restoration including the fuel system where I found some questionable desig
> n features.=C2- During this period (from 1993) I also licensed a few othe
> rs and found it was necessary to do a hot soap and water flush of the fuel
> vent system to remove bug debris.=C2-Many people have noted the fuel feed
> s from the LH tank first.=C2- That is not surprising since the LH=C2- v
> ent system is much shorter than the RH and the tube is 8 mm (6 mm ID) for b
> oth.=C2- Not a huge problem as long as the tubing is internally clean and
> totally free of any damage that could restrict air flow. This is critical!
> =C2- There is also some minor effect favoring LH flow via the shorter fue
> l feed line to the header tank.=C2-=C2-=C2- =C2-The major design pr
> oblem rests with the header tank flapper valves.=C2- There are three of t
> hese valves in the aircraft.=C2- One is in the fuel line from the header
> tank to the fuel pump.=C2- It=99s sole purpose is to direct fuelfro
> m the emerg. (wobble) pump to the engine fuel pump while preventing reverse
> flow back to the header tank.=C2- This is the type of function the valve
> is designed for and it works perfectly because there is a distinct differe
> nce in pressure on each side.=C2- =C2-With reference to the attached ph
> otos note the diameter of the flapper as compared to the diameter of the in
> coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
> open (or close) with fuel flow but pressure, though relatively small, is a
> factor.=C2-=C2- If we start with equal fuel one flapper will open (prob
> ably the LH).=C2- In theory as the pressure from the LH tank and the head
> er tank is reduced at some point the RH will open and the cycle will repeat
> .But, in fact, the LH plus the header tank fuel is actually applying a forc
> e to the valve surface roughly double that of the smaller surface impacted
> by the RH fuel.=C2-I did some rough math based on tank volume and pressur
> es, etc. and came to the following conclusion: - The major reason this syst
> em sort of works is called turbulence!=C2- If you could take off, climb a
> nd fly a trip with never a bump of any kind you will be out of gas with a f
> ull RH tank. =C2-As you probably noted I have modified the valves to allo
> w closing pressure to impact some of the opening surface.=C2- My typical
> fuel imbalance is less than 5 lts.=C2- For me this is a hand filing opera
> tion (though a CNC genius could probably do it).=C2-=C2- You MUST retai
> n a seating ring of the original closing surface.=C2- If you change that
> it will never close properly again due to the geometry. =C2-One of the un
> modified valve photos shows a Chinese character on a wrench flat.=C2- In
> English this reads =9CHINGE=9D and must be at the top.=C2- I
> mproper positioning could well be the cause of serious imbalance.=C2-=C2
> -Cheers;Walt=C2-=C2-=C2-=C2-=C2-
>
> ________________________________ Message 4
> _____________________________________
>
>
> Time: 09:06:58 PM PST US
> From: "Walter Lannon" <wlannon@shaw.ca>
> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>
> Hi Jon;
> Thank you!
> I have never seen the wing tip vent installation but assume that was
> it=99s purpose. Should work as long as it terminates in a
> positive (or neutral) pressure area.
> I seem to remember from my misspent youth that Cessna produced a lightly
> spring loaded vent valve that was installed in the fuel cap. I have
> been intending to
> track that down for years!!!
> We really should have an emergency vent of some type in the CJ. ONE is
> not enough! In the T6/Harvard (and most aircraft) each tank is
> separately vented.
> Over the years I have seen three T6 fuel tanks where you could touch the
> tank bottom from the filler hole due to a plugged vent.
> Cheers;
> Walt
> From: JON BLAKE
> Sent: Monday, December 07, 2020 12:26 PM
> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>
> Good info Walt... many thanks.
> When I first bought my CJ 15 years ago, I was told to wrap the vent on
> the belly with a fine mesh screen to keep the bugs out. I was also told
> that the vents going out to each wing tips were installed by Yakity Yaks
> to help prevent a bug or other debris from causing fuel starvation. Is
> that true? Can you shed any more light on those vents?
>
>
> Jon Blake
> Saber369@comcast.net
>
> On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
> From: Walter Lannon
> Sent: Sunday, December 06, 2020 9:09 PM
> To: yaklist@matronics.com
> Subject: CJ6 uneven fuel flow
> Currently there is a lot of interest in the above subject on the Red
> Star site. Since I have some experience in this area I thought I should
> respond but since it will be a rather long diatribe I thought the Yak
> List might be a better venue.
> My aircraft is a 1966 model CJ6a, one of four I imported from China in
> 1993. Did not start my own restoration until after selling my Harvard 4
> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
> including the fuel system where I found some questionable design
> features. During this period (from 1993) I also licensed a few others
> and found it was necessary to do a hot soap and water flush of the fuel
> vent system to remove bug debris.
> Many people have noted the fuel feeds from the LH tank first. That is
> not surprising since the LH vent system is much shorter than the RH and
> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
> tubing is internally clean and totally free of any damage that could
> restrict air flow. This is critical! There is also some minor effect
> favoring LH flow via the shorter fuel feed line to the header tank.
> The major design problem rests with the header tank flapper valves.
> There are three of these valves in the aircraft. One is in the fuel
> line from the header tank to the fuel pump. It=99s sole purpose
> is to direct fuel
> from the emerg. (wobble) pump to the engine fuel pump while preventing
> reverse flow back to the header tank. This is the type of function the
> valve is designed for and it works perfectly because there is a
> distinct difference in pressure on each side.
> With reference to the attached photos note the diameter of the flapper
> as compared to the diameter of the incoming fuel hole. A true
> =9Cflapper=9D valve is meant to open (or close) with fuel
> flow but pressure, though relatively small, is a factor. If we start
> with equal fuel one flapper will open (probably the LH). In theory as
> the pressure from the LH tank and the header tank is reduced at some
> point the RH will open and the cycle will repeat.
> But, in fact, the LH plus the header tank fuel is actually applying a
> force to the valve surface roughly double that of the smaller surface
> impacted by the RH fuel.
> I did some rough math based on tank volume and pressures, etc. and
> came to the following conclusion: - The major reason this system sort of
> works is called turbulence! If you could take off, climb and fly a trip
> with never a bump of any kind you will be out of gas with a full RH
> tank.
> As you probably noted I have modified the valves to allow closing
> pressure to impact some of the opening surface. My typical fuel
> imbalance is less than 5 lts. For me this is a hand filing operation
> (though a CNC genius could probably do it). You MUST retain a seating
> ring of the original closing surface. If you change that it will never
> close properly again due to the geometry.
> One of the un modified valve photos shows a Chinese character on a
> wrench flat. In English this reads =9CHINGE=9D and must be
> at the top. Improper positioning could well be the cause of serious
> imbalance.
> Cheers;
> Walt
>
>
Message 2
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
Good Morning Yak List
I fly a CJ6 with the bladders so not stock tank or vent piping.
When I was having this problem I consulted another CJ owner with a bladder
system ( you know who you are and thank you) and he pointed out after some
photos were sent to him that my tube extending from the bottom of the plane
was most likely not long enough to be in the slipstream and apply the
pressure to the vent system and the top of the fuel in the tanks. I
extended the tube about 3/8" farther down and it cured my tank imbalance.
Also, what I do about every third flight or so is I put a hose on the vent
tube extending from the bottom of the plane and open one fuel tank at a
time and blow through the system and clear the vent system back to the
tank. I close that tank and open the other and repeat. Sometimes I can
tell I am clearing something from the vent system back into the tank. Most
likely fuel. I dont fly straight and level very long when I go out.
I make sure the ball is centered and pay attention to wings level and I
rarely come back with a fuel imbalance. I did inspect the flapper valves
during one of my condition inspections and made sure they were clean and
freely moving but made no modifications to them. I usually refuel after
the flight and before I put the plane in the hangar. Usually the tanks are
within 1 to 2 gallons of each other... A couple of times, I have come back
after a couple of hours of flight time and one tank was down much farther
than the other. Before I put the plane away , I put the hose on the vent
tube and could tell one tank's vent system was plugged. So the imbalance
made sense.
Hope this helps.
Mark
N621CJ
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On Tue, Dec 8, 2020 at 6:20 AM Craig Payne <yakman285@gmail.com> wrote:
> Some years back the popular fix was to file some notches in the flapper
> valves. To me that seemed to defeat the purpose. Using a little MMO in the
> fuel made me feel better anyway.
>
> Craig Payne
>
> On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server <
> yak-list@matronics.com> wrote:
>
>> *
>>
>> ========================
>> Online Versions of Today's List Digest Archive
>> ========================
>>
>> Today's complete Yak-List Digest can also be found in either of the
>> two Web Links listed below. The .html file includes the Digest formatted
>> in HTML for viewing with a web browser and features Hyperlinked Indexes
>> and Message Navigation. The .txt file includes the plain ASCII version
>> of the Yak-List Digest and can be viewed with a generic text editor
>> such as Notepad or with a web browser.
>>
>> HTML Version:
>>
>>
>> http://www.matronics.com/digest/digestview.php?Style=82701&View=html&Chapter 20-12-07&Archive=Yak
>>
>> Text Version:
>>
>>
>> http://www.matronics.com/digest/digestview.php?Style=82701&View=txt&Chapter 20-12-07&Archive=Yak
>>
>>
>> ======================
>> EMail Version of Today's List Digest Archive
>> ======================
>>
>>
>> ----------------------------------------------------------
>> Yak-List Digest Archive
>> ---
>> Total Messages Posted Mon 12/07/20: 4
>> ----------------------------------------------------------
>>
>>
>> Today's Message Index:
>> ----------------------
>>
>> 1. 10:24 AM - Fw: CJ6 uneven fuel flow (Walter Lannon)
>> 2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow (JON BLAKE)
>> 3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow (Larry Pine)
>> 4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow (Walter Lannon)
>>
>>
>>
>> ________________________________ Message 1
>> _____________________________________
>>
>>
>> Time: 10:24:05 AM PST US
>> From: "Walter Lannon" <wlannon@shaw.ca>
>> Subject: Yak-List: Fw: CJ6 uneven fuel flow
>>
>>
>> From: Walter Lannon
>> Sent: Sunday, December 06, 2020 9:09 PM
>> Subject: CJ6 uneven fuel flow
>>
>> Currently there is a lot of interest in the above subject on the Red
>> Star site. Since I have some experience in this area I thought I should
>> respond but since it will be a rather long diatribe I thought the Yak
>> List might be a better venue.
>>
>> My aircraft is a 1966 model CJ6a, one of four I imported from China in
>> 1993. Did not start my own restoration until after selling my Harvard 4
>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
>> including the fuel system where I found some questionable design
>> features. During this period (from 1993) I also licensed a few others
>> and found it was necessary to do a hot soap and water flush of the fuel
>> vent system to remove bug debris.
>>
>> Many people have noted the fuel feeds from the LH tank first. That is
>> not surprising since the LH vent system is much shorter than the RH and
>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>> tubing is internally clean and totally free of any damage that could
>> restrict air flow. This is critical! There is also some minor effect
>> favoring LH flow via the shorter fuel feed line to the header tank.
>>
>> The major design problem rests with the header tank flapper valves.
>> There are three of these valves in the aircraft. One is in the fuel
>> line from the header tank to the fuel pump. It=99s sole purpose
>> is to direct fuel
>> from the emerg. (wobble) pump to the engine fuel pump while preventing
>> reverse flow back to the header tank. This is the type of function the
>> valve is designed for and it works perfectly because there is a
>> distinct difference in pressure on each side.
>>
>> With reference to the attached photos note the diameter of the flapper
>> as compared to the diameter of the incoming fuel hole. A true
>> =9Cflapper=9D valve is meant to open (or close) with fuel
>> flow but pressure, though relatively small, is a factor. If we start
>> with equal fuel one flapper will open (probably the LH). In theory as
>> the pressure from the LH tank and the header tank is reduced at some
>> point the RH will open and the cycle will repeat.
>> But, in fact, the LH plus the header tank fuel is actually applying a
>> force to the valve surface roughly double that of the smaller surface
>> impacted by the RH fuel.
>>
>> I did some rough math based on tank volume and pressures, etc. and came
>> to the following conclusion: - The major reason this system sort of
>> works is called turbulence! If you could take off, climb and fly a trip
>> with never a bump of any kind you will be out of gas with a full RH
>> tank.
>>
>> As you probably noted I have modified the valves to allow closing
>> pressure to impact some of the opening surface. My typical fuel
>> imbalance is less than 5 lts. For me this is a hand filing operation
>> (though a CNC genius could probably do it). You MUST retain a seating
>> ring of the original closing surface. If you change that it will never
>> close properly again due to the geometry.
>>
>> One of the un modified valve photos shows a Chinese character on a
>> wrench flat. In English this reads =9CHINGE=9D and must be
>> at the top. Improper positioning could well be the cause of serious
>> imbalance.
>>
>>
>> Cheers;
>> Walt
>>
>>
>> ________________________________ Message 2
>> _____________________________________
>>
>>
>> Time: 12:28:05 PM PST US
>> From: JON BLAKE <saber369@comcast.net>
>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>
>> Good info Walt... many thanks.
>>
>> When I first bought my CJ 15 years ago, I was told to wrap the vent on
>> the
>> belly with a fine mesh screen to keep the bugs out. I was also told that
>> t
>> he vents going out to each wing tips were installed by Yakity Yaks to
>> help
>> prevent a bug or other debris from causing fuel starvation. Is that
>> true?
>> Can you shed any more light on those vents?
>>
>>
>> Jon Blake
>> Saber369@comcast.net
>>
>> > On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>> >
>> >
>> >
>> >
>> > From: Walter Lannon mailto:wlannon@shaw.ca
>> > Sent: Sunday, December 06, 2020 9:09 PM
>> > To: yaklist@matronics.com mailto:yaklist@matronics.com
>> > Subject: CJ6 uneven fuel flow
>> >
>> > Currently there is a lot of interest in the above subject on the
>> Red
>> Star site. Since I have some experience in this area I thought I should
>> re
>> spond but since it will be a rather long diatribe I thought the Yak List
>> mi
>> ght be a better venue.
>> >
>> > My aircraft is a 1966 model CJ6a, one of four I imported from China
>> i
>> n 1993. Did not start my own restoration until after selling my Harvard
>> 4
>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
>> in
>> cluding the fuel system where I found some questionable design features.
>> D
>> uring this period (from 1993) I also licensed a few others and found it
>> was
>> necessary to do a hot soap and water flush of the fuel vent system to
>> remo
>> ve bug debris.
>> >
>> > Many people have noted the fuel feeds from the LH tank first. That
>> i
>> s not surprising since the LH vent system is much shorter than the RH
>> and
>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>> > tubing is internally clean and totally free of any damage that
>> could
>> restrict air flow. This is critical! There is also some minor effect
>> favor
>> ing LH flow via the shorter fuel feed line to the header tank.
>> >
>> > The major design problem rests with the header tank flapper
>> valves.
>> There are three of these valves in the aircraft. One is in the fuel line
>> f
>> rom the header tank to the fuel pump. It=99s sole purpose is to dire
>> ct fuel
>> > from the emerg. (wobble) pump to the engine fuel pump while
>> preventin
>> g reverse flow back to the header tank. This is the type of function the
>> v
>> alve is designed for and it works perfectly because there is a
>> > distinct difference in pressure on each side.
>> >
>> > With reference to the attached photos note the diameter of the
>> flappe
>> r as compared to the diameter of the incoming fuel hole. A true =9Cf
>> lapper=9D valve is meant to open (or close) with fuel flow but pressu
>> re, though relatively small, is a factor. If we start with equal fuel
>> one
>> flapper will open (probably the LH). In theory as the pressure from the
>> L
>> H tank and the header tank is reduced at some point the RH will open and
>> th
>> e cycle will repeat.
>> > But, in fact, the LH plus the header tank fuel is actually applying
>> a
>> force to the valve surface roughly double that of the smaller surface
>> impa
>> cted by the RH fuel.
>> >
>> > I did some rough math based on tank volume and pressures, etc. and
>> ca
>> me to the following conclusion: - The major reason this system sort of
>> work
>> s is called turbulence! If you could take off, climb and fly a trip with
>> n
>> ever a bump of any kind you will be out of gas with a full RH tank.
>> >
>> > As you probably noted I have modified the valves to allow closing
>> pre
>> ssure to impact some of the opening surface. My typical fuel imbalance
>> is
>> less than 5 lts. For me this is a hand filing operation (though a CNC
>> geni
>> us could probably do it). You MUST retain a seating ring of the
>> original
>> closing surface. If you change that it will never close properly again
>> due
>> to the geometry.
>> >
>> > One of the un modified valve photos shows a Chinese character on a
>> wr
>> ench flat. In English this reads =9CHINGE=9D and must be at th
>> e top. Improper positioning could well be the cause of serious imbalance.
>> >
>> >
>> > Cheers;
>> > Walt
>> >
>> >
>> >
>> >
>> >
>> >
>>
>> ________________________________ Message 3
>> _____________________________________
>>
>>
>> Time: 01:30:00 PM PST US
>> From: Larry Pine <threein60@yahoo.com>
>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>
>>
>> Great write-up on this. Let me add a little learned knowledge to this
>> discu
>> ssion. I have no issues with what Walt stated but a few years ago I had
>> fue
>> l starvation while on the ground. I could start the engine on my
>> electrical
>> boost pump but the minute I shut it off, the engine would die. I checked
>> f
>> uel levels, I removed and cleaned the fuel strainer and checked for flow,
>> s
>> till nothing. Only when I removed the flapper valve under the floor, the
>> on
>> e that feeds the wobble pump, I found the hinge in this flapper was worn
>> an
>> d could rotate to a place where it would get stuck closed. This was the
>> fir
>> st I have ever hear of this happening. I cleaned and lightly refaced both
>> t
>> he flapper and flapper seat. I then replaced the worn hinge pivot rod
>> with
>> a new brass one. I have plans to take apart this valve again during this
>> mo
>> nths annual and see if these is any wear taking place on the hinge rod.
>> Luc
>> ky I found this on the ground but confident had this happened in flight,
>> my
>> electric driven pump would have supplied enough fuel to get me back
>> safely
>> . Still some thing that should be examined.
>>
>> I have bladder tanks so my vents are extended to their respective wing
>> tips
>> with a separate vent for the header tank. I find that I tend to fly more
>> p
>> ressure on my left rudder because my knee board is on my right and
>> lifting
>> my right knee a little makes writing easier. This tends to cause a
>> noticeab
>> le fuel difference over a 2 hour period. I know, bad pilot bad. Very
>> early
>> on before I had my bladder tanks installed, I had to do an emergency
>> divert
>> because my one tank was almost dry and the opposite tank wasn't moving
>> the
>> needle yet. Only after landing I noticed the needle move. Constant fuel
>> ma
>> nagement has become the norm. I optioned to not install the vent shut off
>> v
>> alues after and incident I had with another RPAer. This pilot closed one
>> of
>> his vents to overcome the fuel flow difference and forgot to open the
>> vent
>> again. On roll out with the engine pulled to ideal, the engine died on
>> the
>> runway. It would start but than die again. When we got it to parking, we
>> n
>> oticed one bladder tank was sucked flat and dry..... The same side with
>> the
>> closed vent. Human factors are human factors! Unless you design a system
>> t
>> o incorporate some warning when the pressure builds or the vent is closed
>> i
>> ndication, this only complicates memory items that needs to be attended
>> and
>> eventually can lead to failures.
>>
>> Larry Pine On Monday, December 7, 2020, 10:48:19 AM PST, Walter
>> Lannon
>> <wlannon@shaw.ca> wrote:
>>
>> =C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020 9:09 PMTo:
>> yaklist@matronics.com Subject: CJ6 uneven fuel flow=C2-Currently there i
>> s a lot of interest in the above subject on the Red Star site.=C2- Since
>> I have some experience in this area I thought I should respond but since
>> it
>> will be a rather long diatribe I thought the Yak List might be a better
>> ve
>> nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported from Chi
>> na in 1993.=C2- Did not start my own restoration until after selling my H
>> arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 100%
>> restoration including the fuel system where I found some questionable
>> desig
>> n features.=C2- During this period (from 1993) I also licensed a few othe
>> rs and found it was necessary to do a hot soap and water flush of the
>> fuel
>> vent system to remove bug debris.=C2-Many people have noted the fuel feed
>> s from the LH tank first.=C2- That is not surprising since the LH=C2- v
>> ent system is much shorter than the RH and the tube is 8 mm (6 mm ID) for
>> b
>> oth.=C2- Not a huge problem as long as the tubing is internally clean and
>> totally free of any damage that could restrict air flow. This is
>> critical!
>> =C2- There is also some minor effect favoring LH flow via the shorter fue
>> l feed line to the header tank.=C2-=C2-=C2- =C2-The major design pr
>> oblem rests with the header tank flapper valves.=C2- There are three of t
>> hese valves in the aircraft.=C2- One is in the fuel line from the header
>> tank to the fuel pump.=C2- It=99s sole purpose is to direct fuelfro
>> m the emerg. (wobble) pump to the engine fuel pump while preventing
>> reverse
>> flow back to the header tank.=C2- This is the type of function the valve
>> is designed for and it works perfectly because there is a distinct
>> differe
>> nce in pressure on each side.=C2- =C2-With reference to the attached ph
>> otos note the diameter of the flapper as compared to the diameter of the
>> in
>> coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
>> open (or close) with fuel flow but pressure, though relatively small, is
>> a
>> factor.=C2-=C2- If we start with equal fuel one flapper will open (prob
>> ably the LH).=C2- In theory as the pressure from the LH tank and the head
>> er tank is reduced at some point the RH will open and the cycle will
>> repeat
>> .But, in fact, the LH plus the header tank fuel is actually applying a
>> forc
>> e to the valve surface roughly double that of the smaller surface
>> impacted
>> by the RH fuel.=C2-I did some rough math based on tank volume and pressur
>> es, etc. and came to the following conclusion: - The major reason this
>> syst
>> em sort of works is called turbulence!=C2- If you could take off, climb a
>> nd fly a trip with never a bump of any kind you will be out of gas with a
>> f
>> ull RH tank. =C2-As you probably noted I have modified the valves to allo
>> w closing pressure to impact some of the opening surface.=C2- My typical
>> fuel imbalance is less than 5 lts.=C2- For me this is a hand filing opera
>> tion (though a CNC genius could probably do it).=C2-=C2- You MUST retai
>> n a seating ring of the original closing surface.=C2- If you change that
>> it will never close properly again due to the geometry. =C2-One of the un
>> modified valve photos shows a Chinese character on a wrench flat.=C2- In
>> English this reads =9CHINGE=9D and must be at the top.=C2- I
>> mproper positioning could well be the cause of serious imbalance.=C2-=C2
>> -Cheers;Walt=C2-=C2-=C2-=C2-=C2-
>>
>> ________________________________ Message 4
>> _____________________________________
>>
>>
>> Time: 09:06:58 PM PST US
>> From: "Walter Lannon" <wlannon@shaw.ca>
>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>
>> Hi Jon;
>> Thank you!
>> I have never seen the wing tip vent installation but assume that was
>> it=99s purpose. Should work as long as it terminates in a
>> positive (or neutral) pressure area.
>> I seem to remember from my misspent youth that Cessna produced a lightly
>> spring loaded vent valve that was installed in the fuel cap. I have
>> been intending to
>> track that down for years!!!
>> We really should have an emergency vent of some type in the CJ. ONE is
>> not enough! In the T6/Harvard (and most aircraft) each tank is
>> separately vented.
>> Over the years I have seen three T6 fuel tanks where you could touch the
>> tank bottom from the filler hole due to a plugged vent.
>> Cheers;
>> Walt
>> From: JON BLAKE
>> Sent: Monday, December 07, 2020 12:26 PM
>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>
>> Good info Walt... many thanks.
>> When I first bought my CJ 15 years ago, I was told to wrap the vent on
>> the belly with a fine mesh screen to keep the bugs out. I was also told
>> that the vents going out to each wing tips were installed by Yakity Yaks
>> to help prevent a bug or other debris from causing fuel starvation. Is
>> that true? Can you shed any more light on those vents?
>>
>>
>> Jon Blake
>> Saber369@comcast.net
>>
>> On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>> From: Walter Lannon
>> Sent: Sunday, December 06, 2020 9:09 PM
>> To: yaklist@matronics.com
>> Subject: CJ6 uneven fuel flow
>> Currently there is a lot of interest in the above subject on the Red
>> Star site. Since I have some experience in this area I thought I should
>> respond but since it will be a rather long diatribe I thought the Yak
>> List might be a better venue.
>> My aircraft is a 1966 model CJ6a, one of four I imported from China in
>> 1993. Did not start my own restoration until after selling my Harvard 4
>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
>> including the fuel system where I found some questionable design
>> features. During this period (from 1993) I also licensed a few others
>> and found it was necessary to do a hot soap and water flush of the fuel
>> vent system to remove bug debris.
>> Many people have noted the fuel feeds from the LH tank first. That is
>> not surprising since the LH vent system is much shorter than the RH and
>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>> tubing is internally clean and totally free of any damage that could
>> restrict air flow. This is critical! There is also some minor effect
>> favoring LH flow via the shorter fuel feed line to the header tank.
>> The major design problem rests with the header tank flapper valves.
>> There are three of these valves in the aircraft. One is in the fuel
>> line from the header tank to the fuel pump. It=99s sole purpose
>> is to direct fuel
>> from the emerg. (wobble) pump to the engine fuel pump while preventing
>> reverse flow back to the header tank. This is the type of function the
>> valve is designed for and it works perfectly because there is a
>> distinct difference in pressure on each side.
>> With reference to the attached photos note the diameter of the flapper
>> as compared to the diameter of the incoming fuel hole. A true
>> =9Cflapper=9D valve is meant to open (or close) with fuel
>> flow but pressure, though relatively small, is a factor. If we start
>> with equal fuel one flapper will open (probably the LH). In theory as
>> the pressure from the LH tank and the header tank is reduced at some
>> point the RH will open and the cycle will repeat.
>> But, in fact, the LH plus the header tank fuel is actually applying a
>> force to the valve surface roughly double that of the smaller surface
>> impacted by the RH fuel.
>> I did some rough math based on tank volume and pressures, etc. and
>> came to the following conclusion: - The major reason this system sort of
>> works is called turbulence! If you could take off, climb and fly a trip
>> with never a bump of any kind you will be out of gas with a full RH
>> tank.
>> As you probably noted I have modified the valves to allow closing
>> pressure to impact some of the opening surface. My typical fuel
>> imbalance is less than 5 lts. For me this is a hand filing operation
>> (though a CNC genius could probably do it). You MUST retain a seating
>> ring of the original closing surface. If you change that it will never
>> close properly again due to the geometry.
>> One of the un modified valve photos shows a Chinese character on a
>> wrench flat. In English this reads =9CHINGE=9D and must be
>> at the top. Improper positioning could well be the cause of serious
>> imbalance.
>> Cheers;
>> Walt
>>
>>
>>
>> ==========
>> List" rel="noreferrer" target="_blank">
>> http://www.matronics.com/Navigator?Yak-List
>> ==========
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>> eferrer" target="_blank">http://forums.matronics.com
>> ==========
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>> errer" target="_blank">http://wiki.matronics.com
>> ==========
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>> -Matt Dralle, List Admin.
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>> ==========
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
Hi Mark;
When you =9Cblow through the system=9D are you using shop
air? If so at what pressure?
Do you dis-connect the header tank vent line? Applying air press to
the header will close both flappers and leave the only pressure relief
to the fuel to engine outlet. Not sure if that will provide adequate
relief.
Your header tank may have grown a bit larger.
Walt
From: Mark Pennington
Sent: Tuesday, December 08, 2020 3:55 AM
Subject: Re: Yak-List: Re: Yak-List Digest: 4 Msgs - 12/07/20
Good Morning Yak List
I fly a CJ6 with the bladders so not stock tank or vent piping.
When I was having this problem I consulted another CJ owner with a
bladder system ( you know who you are and thank you) and he pointed out
after some photos were sent to him that my tube extending from the
bottom of the plane was most likely not long enough to be in the
slipstream and apply the pressure to the vent system and the top of the
fuel in the tanks. I extended the tube about 3/8" farther down and it
cured my tank imbalance. Also, what I do about every third flight or so
is I put a hose on the vent tube extending from the bottom of the plane
and open one fuel tank at a time and blow through the system and clear
the vent system back to the tank. I close that tank and open the other
and repeat. Sometimes I can tell I am clearing something from the vent
system back into the tank. Most likely fuel. I dont fly straight and
level very long when I go out.
I make sure the ball is centered and pay attention to wings level and I
rarely come back with a fuel imbalance. I did inspect the flapper
valves during one of my condition inspections and made sure they were
clean and freely moving but made no modifications to them. I usually
refuel after the flight and before I put the plane in the hangar.
Usually the tanks are within 1 to 2 gallons of each other... A couple of
times, I have come back after a couple of hours of flight time and one
tank was down much farther than the other. Before I put the plane away
, I put the hose on the vent tube and could tell one tank's vent system
was plugged. So the imbalance made sense.
Hope this helps.
Mark
N621CJ
Virus-free. www.avast.com
On Tue, Dec 8, 2020 at 6:20 AM Craig Payne <yakman285@gmail.com> wrote:
Some years back the popular fix was to file some notches in the
flapper valves. To me that seemed to defeat the purpose. Using a little
MMO in the fuel made me feel better anyway.
Craig Payne
On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server
<yak-list@matronics.com> wrote:
*
Online Versions of Today's List Digest Archive
Today's complete Yak-List Digest can also be found in either of the
two Web Links listed below. The .html file includes the Digest
formatted
in HTML for viewing with a web browser and features Hyperlinked
Indexes
and Message Navigation. The .txt file includes the plain ASCII
version
of the Yak-List Digest and can be viewed with a generic text editor
such as Notepad or with a web browser.
HTML Version:
http://www.matronics.com/digest/digestview.php?Style=82701&View=html&
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hapter 20-12-07&Archive=Yak
======================
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======================
----------------------------------------------------------
Yak-List Digest Archive
---
Total Messages Posted Mon 12/07/20: 4
----------------------------------------------------------
Today's Message Index:
----------------------
1. 10:24 AM - Fw: CJ6 uneven fuel flow (Walter Lannon)
2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow (JON BLAKE)
3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow (Larry Pine)
4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow (Walter Lannon)
________________________________ Message 1
_____________________________________
Time: 10:24:05 AM PST US
From: "Walter Lannon" <wlannon@shaw.ca>
Subject: Yak-List: Fw: CJ6 uneven fuel flow
From: Walter Lannon
Sent: Sunday, December 06, 2020 9:09 PM
Subject: CJ6 uneven fuel flow
Currently there is a lot of interest in the above subject on the Red
Star site. Since I have some experience in this area I thought I
should
respond but since it will be a rather long diatribe I thought the
Yak
List might be a better venue.
My aircraft is a 1966 model CJ6a, one of four I imported from China
in
1993. Did not start my own restoration until after selling my
Harvard 4
in 2006 (after 30 years!) It was a 6 year (off and on) 100%
restoration
including the fuel system where I found some questionable design
features. During this period (from 1993) I also licensed a few
others
and found it was necessary to do a hot soap and water flush of the
fuel
vent system to remove bug debris.
Many people have noted the fuel feeds from the LH tank first. That
is
not surprising since the LH vent system is much shorter than the RH
and
the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as
the
tubing is internally clean and totally free of any damage that could
restrict air flow. This is critical! There is also some minor
effect
favoring LH flow via the shorter fuel feed line to the header tank.
The major design problem rests with the header tank flapper valves.
There are three of these valves in the aircraft. One is in the fuel
line from the header tank to the fuel pump. It=99s sole purpose
is to direct fuel
from the emerg. (wobble) pump to the engine fuel pump while
preventing
reverse flow back to the header tank. This is the type of function
the
valve is designed for and it works perfectly because there is a
distinct difference in pressure on each side.
With reference to the attached photos note the diameter of the
flapper
as compared to the diameter of the incoming fuel hole. A true
=9Cflapper=9D valve is meant to open (or close) with fuel
flow but pressure, though relatively small, is a factor. If we
start
with equal fuel one flapper will open (probably the LH). In theory
as
the pressure from the LH tank and the header tank is reduced at some
point the RH will open and the cycle will repeat.
But, in fact, the LH plus the header tank fuel is actually applying
a
force to the valve surface roughly double that of the smaller
surface
impacted by the RH fuel.
I did some rough math based on tank volume and pressures, etc. and
came
to the following conclusion: - The major reason this system sort of
works is called turbulence! If you could take off, climb and fly a
trip
with never a bump of any kind you will be out of gas with a full RH
tank.
As you probably noted I have modified the valves to allow closing
pressure to impact some of the opening surface. My typical fuel
imbalance is less than 5 lts. For me this is a hand filing
operation
(though a CNC genius could probably do it). You MUST retain a
seating
ring of the original closing surface. If you change that it will
never
close properly again due to the geometry.
One of the un modified valve photos shows a Chinese character on a
wrench flat. In English this reads =9CHINGE=9D and must be
at the top. Improper positioning could well be the cause of serious
imbalance.
Cheers;
Walt
________________________________ Message 2
_____________________________________
Time: 12:28:05 PM PST US
From: JON BLAKE <saber369@comcast.net>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Good info Walt... many thanks.
When I first bought my CJ 15 years ago, I was told to wrap the vent
on the
belly with a fine mesh screen to keep the bugs out. I was also told
that t
he vents going out to each wing tips were installed by Yakity Yaks
to help
prevent a bug or other debris from causing fuel starvation. Is that
true?
Can you shed any more light on those vents?
Jon Blake
Saber369@comcast.net
> On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>
>
>
>
> From: Walter Lannon mailto:wlannon@shaw.ca
> Sent: Sunday, December 06, 2020 9:09 PM
> To: yaklist@matronics.com mailto:yaklist@matronics.com
> Subject: CJ6 uneven fuel flow
>
> Currently there is a lot of interest in the above subject on
the Red
Star site. Since I have some experience in this area I thought I
should re
spond but since it will be a rather long diatribe I thought the Yak
List mi
ght be a better venue.
>
> My aircraft is a 1966 model CJ6a, one of four I imported from
China i
n 1993. Did not start my own restoration until after selling my
Harvard 4
in 2006 (after 30 years!) It was a 6 year (off and on) 100%
restoration in
cluding the fuel system where I found some questionable design
features. D
uring this period (from 1993) I also licensed a few others and found
it was
necessary to do a hot soap and water flush of the fuel vent system
to remo
ve bug debris.
>
> Many people have noted the fuel feeds from the LH tank first.
That i
s not surprising since the LH vent system is much shorter than the
RH and
the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as
the
> tubing is internally clean and totally free of any damage that
could
restrict air flow. This is critical! There is also some minor
effect favor
ing LH flow via the shorter fuel feed line to the header tank.
>
> The major design problem rests with the header tank flapper
valves.
There are three of these valves in the aircraft. One is in the fuel
line f
rom the header tank to the fuel pump. It=99s sole purpose is to
dire
ct fuel
> from the emerg. (wobble) pump to the engine fuel pump while
preventin
g reverse flow back to the header tank. This is the type of
function the v
alve is designed for and it works perfectly because there is a
> distinct difference in pressure on each side.
>
> With reference to the attached photos note the diameter of the
flappe
r as compared to the diameter of the incoming fuel hole. A true
=9Cf
lapper=9D valve is meant to open (or close) with fuel flow but
pressu
re, though relatively small, is a factor. If we start with equal
fuel one
flapper will open (probably the LH). In theory as the pressure from
the L
H tank and the header tank is reduced at some point the RH will open
and th
e cycle will repeat.
> But, in fact, the LH plus the header tank fuel is actually
applying a
force to the valve surface roughly double that of the smaller
surface impa
cted by the RH fuel.
>
> I did some rough math based on tank volume and pressures, etc.
and ca
me to the following conclusion: - The major reason this system sort
of work
s is called turbulence! If you could take off, climb and fly a trip
with n
ever a bump of any kind you will be out of gas with a full RH tank.
>
> As you probably noted I have modified the valves to allow
closing pre
ssure to impact some of the opening surface. My typical fuel
imbalance is
less than 5 lts. For me this is a hand filing operation (though a
CNC geni
us could probably do it). You MUST retain a seating ring of the
original
closing surface. If you change that it will never close properly
again due
to the geometry.
>
> One of the un modified valve photos shows a Chinese character
on a wr
ench flat. In English this reads =9CHINGE=9D and must be at th
e top. Improper positioning could well be the cause of serious
imbalance.
>
>
> Cheers;
> Walt
>
>
>
>
>
>
________________________________ Message 3
_____________________________________
Time: 01:30:00 PM PST US
From: Larry Pine <threein60@yahoo.com>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Great write-up on this. Let me add a little learned knowledge to
this discu
ssion. I have no issues with what Walt stated but a few years ago I
had fue
l starvation while on the ground. I could start the engine on my
electrical
boost pump but the minute I shut it off, the engine would die. I
checked f
uel levels, I removed and cleaned the fuel strainer and checked for
flow, s
till nothing. Only when I removed the flapper valve under the floor,
the on
e that feeds the wobble pump, I found the hinge in this flapper was
worn an
d could rotate to a place where it would get stuck closed. This was
the fir
st I have ever hear of this happening. I cleaned and lightly refaced
both t
he flapper and flapper seat. I then replaced the worn hinge pivot
rod with
a new brass one. I have plans to take apart this valve again during
this mo
nths annual and see if these is any wear taking place on the hinge
rod. Luc
ky I found this on the ground but confident had this happened in
flight, my
electric driven pump would have supplied enough fuel to get me back
safely
. Still some thing that should be examined.
I have bladder tanks so my vents are extended to their respective
wing tips
with a separate vent for the header tank. I find that I tend to fly
more p
ressure on my left rudder because my knee board is on my right and
lifting
my right knee a little makes writing easier. This tends to cause a
noticeab
le fuel difference over a 2 hour period. I know, bad pilot bad. Very
early
on before I had my bladder tanks installed, I had to do an emergency
divert
because my one tank was almost dry and the opposite tank wasn't
moving the
needle yet. Only after landing I noticed the needle move. Constant
fuel ma
nagement has become the norm. I optioned to not install the vent
shut off v
alues after and incident I had with another RPAer. This pilot closed
one of
his vents to overcome the fuel flow difference and forgot to open
the vent
again. On roll out with the engine pulled to ideal, the engine died
on the
runway. It would start but than die again. When we got it to
parking, we n
oticed one bladder tank was sucked flat and dry..... The same side
with the
closed vent. Human factors are human factors! Unless you design a
system t
o incorporate some warning when the pressure builds or the vent is
closed i
ndication, this only complicates memory items that needs to be
attended and
eventually can lead to failures.
Larry Pine On Monday, December 7, 2020, 10:48:19 AM PST, Walter
Lannon
<wlannon@shaw.ca> wrote:
=C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020 9:09
PMTo:
yaklist@matronics.com Subject: CJ6 uneven fuel flow=C2-Currently
there i
s a lot of interest in the above subject on the Red Star site.=C2-
Since
I have some experience in this area I thought I should respond but
since it
will be a rather long diatribe I thought the Yak List might be a
better ve
nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported
from Chi
na in 1993.=C2- Did not start my own restoration until after
selling my H
arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and
on) 100%
restoration including the fuel system where I found some
questionable desig
n features.=C2- During this period (from 1993) I also licensed a
few othe
rs and found it was necessary to do a hot soap and water flush of
the fuel
vent system to remove bug debris.=C2-Many people have noted the
fuel feed
s from the LH tank first.=C2- That is not surprising since the
LH=C2- v
ent system is much shorter than the RH and the tube is 8 mm (6 mm
ID) for b
oth.=C2- Not a huge problem as long as the tubing is internally
clean and
totally free of any damage that could restrict air flow. This is
critical!
=C2- There is also some minor effect favoring LH flow via the
shorter fue
l feed line to the header tank.=C2-=C2-=C2- =C2-The major
design pr
oblem rests with the header tank flapper valves.=C2- There are
three of t
hese valves in the aircraft.=C2- One is in the fuel line from the
header
tank to the fuel pump.=C2- It=99s sole purpose is to direct
fuelfro
m the emerg. (wobble) pump to the engine fuel pump while preventing
reverse
flow back to the header tank.=C2- This is the type of function the
valve
is designed for and it works perfectly because there is a distinct
differe
nce in pressure on each side.=C2- =C2-With reference to the
attached ph
otos note the diameter of the flapper as compared to the diameter of
the in
coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
open (or close) with fuel flow but pressure, though relatively
small, is a
factor.=C2-=C2- If we start with equal fuel one flapper will
open (prob
ably the LH).=C2- In theory as the pressure from the LH tank and
the head
er tank is reduced at some point the RH will open and the cycle will
repeat
.But, in fact, the LH plus the header tank fuel is actually applying
a forc
e to the valve surface roughly double that of the smaller surface
impacted
by the RH fuel.=C2-I did some rough math based on tank volume and
pressur
es, etc. and came to the following conclusion: - The major reason
this syst
em sort of works is called turbulence!=C2- If you could take off,
climb a
nd fly a trip with never a bump of any kind you will be out of gas
with a f
ull RH tank. =C2-As you probably noted I have modified the valves
to allo
w closing pressure to impact some of the opening surface.=C2- My
typical
fuel imbalance is less than 5 lts.=C2- For me this is a hand
filing opera
tion (though a CNC genius could probably do it).=C2-=C2- You
MUST retai
n a seating ring of the original closing surface.=C2- If you
change that
it will never close properly again due to the geometry. =C2-One of
the un
modified valve photos shows a Chinese character on a wrench
flat.=C2- In
English this reads =9CHINGE=9D and must be at the top.=C2- I
mproper positioning could well be the cause of serious
imbalance.=C2-=C2
-Cheers;Walt=C2-=C2-=C2-=C2-=C2-
________________________________ Message 4
_____________________________________
Time: 09:06:58 PM PST US
From: "Walter Lannon" <wlannon@shaw.ca>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Hi Jon;
Thank you!
I have never seen the wing tip vent installation but assume that was
it=99s purpose. Should work as long as it terminates in a
positive (or neutral) pressure area.
I seem to remember from my misspent youth that Cessna produced a
lightly
spring loaded vent valve that was installed in the fuel cap. I have
been intending to
track that down for years!!!
We really should have an emergency vent of some type in the CJ. ONE
is
not enough! In the T6/Harvard (and most aircraft) each tank is
separately vented.
Over the years I have seen three T6 fuel tanks where you could touch
the
tank bottom from the filler hole due to a plugged vent.
Cheers;
Walt
From: JON BLAKE
Sent: Monday, December 07, 2020 12:26 PM
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Good info Walt... many thanks.
When I first bought my CJ 15 years ago, I was told to wrap the vent
on
the belly with a fine mesh screen to keep the bugs out. I was also
told
that the vents going out to each wing tips were installed by Yakity
Yaks
to help prevent a bug or other debris from causing fuel starvation.
Is
that true? Can you shed any more light on those vents?
Jon Blake
Saber369@comcast.net
On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
From: Walter Lannon
Sent: Sunday, December 06, 2020 9:09 PM
To: yaklist@matronics.com
Subject: CJ6 uneven fuel flow
Currently there is a lot of interest in the above subject on the
Red
Star site. Since I have some experience in this area I thought I
should
respond but since it will be a rather long diatribe I thought the
Yak
List might be a better venue.
My aircraft is a 1966 model CJ6a, one of four I imported from
China in
1993. Did not start my own restoration until after selling my
Harvard 4
in 2006 (after 30 years!) It was a 6 year (off and on) 100%
restoration
including the fuel system where I found some questionable design
features. During this period (from 1993) I also licensed a few
others
and found it was necessary to do a hot soap and water flush of the
fuel
vent system to remove bug debris.
Many people have noted the fuel feeds from the LH tank first.
That is
not surprising since the LH vent system is much shorter than the RH
and
the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as
the
tubing is internally clean and totally free of any damage that
could
restrict air flow. This is critical! There is also some minor
effect
favoring LH flow via the shorter fuel feed line to the header tank.
The major design problem rests with the header tank flapper
valves.
There are three of these valves in the aircraft. One is in the fuel
line from the header tank to the fuel pump. It=99s sole purpose
is to direct fuel
from the emerg. (wobble) pump to the engine fuel pump while
preventing
reverse flow back to the header tank. This is the type of function
the
valve is designed for and it works perfectly because there is a
distinct difference in pressure on each side.
With reference to the attached photos note the diameter of the
flapper
as compared to the diameter of the incoming fuel hole. A true
=9Cflapper=9D valve is meant to open (or close) with fuel
flow but pressure, though relatively small, is a factor. If we
start
with equal fuel one flapper will open (probably the LH). In theory
as
the pressure from the LH tank and the header tank is reduced at some
point the RH will open and the cycle will repeat.
But, in fact, the LH plus the header tank fuel is actually
applying a
force to the valve surface roughly double that of the smaller
surface
impacted by the RH fuel.
I did some rough math based on tank volume and pressures, etc. and
came to the following conclusion: - The major reason this system
sort of
works is called turbulence! If you could take off, climb and fly a
trip
with never a bump of any kind you will be out of gas with a full RH
tank.
As you probably noted I have modified the valves to allow closing
pressure to impact some of the opening surface. My typical fuel
imbalance is less than 5 lts. For me this is a hand filing
operation
(though a CNC genius could probably do it). You MUST retain a
seating
ring of the original closing surface. If you change that it will
never
close properly again due to the geometry.
One of the un modified valve photos shows a Chinese character on a
wrench flat. In English this reads =9CHINGE=9D and must be
at the top. Improper positioning could well be the cause of serious
imbalance.
Cheers;
Walt
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
Hi Mark-
I have started the same habit of periodically blowing air through the vent s
ystem as I believe some fuel migrates into the line sometimes (despite a che
ck valve and having to go up hill around the loop in the cockpit). Make sur
e fuel caps are off and have a second person feel for air at each bladder as
air is blown into the belly tube. You can also check each cockpit vent con
trol (left and right) as each should shut off and air not felt at the tank a
s you select off in the cockpit. Simple check that has kept tanks flowing r
elatively evenly and gives me peace of mind.
Hoot
Sent from my iPhone
> On Dec 8, 2020, at 2:34 PM, Walter Lannon <wlannon@shaw.ca> wrote:
>
> =EF=BB
> Hi Mark;
>
> When you =9Cblow through the system=9D are you using shop air?
If so at what pressure?
>
> Do you dis-connect the header tank vent line? Applying air press to the h
eader will close both flappers and leave the only pressure relief to the fue
l to engine outlet. Not sure if that will provide adequate relief.
> Your header tank may have grown a bit larger.
>
> Walt
>
> From: Mark Pennington
> Sent: Tuesday, December 08, 2020 3:55 AM
> To: yak-list@matronics.com
> Subject: Re: Yak-List: Re: Yak-List Digest: 4 Msgs - 12/07/20
>
> Good Morning Yak List
>
> I fly a CJ6 with the bladders so not stock tank or vent piping.
>
> When I was having this problem I consulted another CJ owner with a bladder
system ( you know who you are and thank you) and he pointed out after some
photos were sent to him that my tube extending from the bottom of the plane
was most likely not long enough to be in the slipstream and apply the press
ure to the vent system and the top of the fuel in the tanks. I extended the
tube about 3/8" farther down and it cured my tank imbalance. Also, what I d
o about every third flight or so is I put a hose on the vent tube extending f
rom the bottom of the plane and open one fuel tank at a time and blow throug
h the system and clear the vent system back to the tank. I close that tank a
nd open the other and repeat. Sometimes I can tell I am clearing something f
rom the vent system back into the tank. Most likely fuel. I dont fly strai
ght and level very long when I go out.
>
> I make sure the ball is centered and pay attention to wings level and I ra
rely come back with a fuel imbalance. I did inspect the flapper valves duri
ng one of my condition inspections and made sure they were clean and freely m
oving but made no modifications to them. I usually refuel after the flight
and before I put the plane in the hangar. Usually the tanks are within 1 t
o 2 gallons of each other... A couple of times, I have come back after a co
uple of hours of flight time and one tank was down much farther than the oth
er. Before I put the plane away , I put the hose on the vent tube and could
tell one tank's vent system was plugged. So the imbalance made sense.
>
> Hope this helps.
>
> Mark
> N621CJ
>
>
>
>
>
> Virus-free. www.avast.com
>
>> On Tue, Dec 8, 2020 at 6:20 AM Craig Payne <yakman285@gmail.com> wrote:
>> Some years back the popular fix was to file some notches in the flapper v
alves. To me that seemed to defeat the purpose. Using a little MMO in the fu
el made me feel better anyway.
>>
>> Craig Payne
>>
>> On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server <yak-list@matronics
.com> wrote:
>>> *
>>>
>>> ========================
>>> Online Versions of Today's List Digest Archive
>>> ========================
>>>
>>> Today's complete Yak-List Digest can also be found in either of the
>>> two Web Links listed below. The .html file includes the Digest formatte
d
>>> in HTML for viewing with a web browser and features Hyperlinked Indexes
>>> and Message Navigation. The .txt file includes the plain ASCII version
>>> of the Yak-List Digest and can be viewed with a generic text editor
>>> such as Notepad or with a web browser.
>>>
>>> HTML Version:
>>>
>>> http://www.matronics.com/digest/digestview.php?Style=82701&View=
html&Chapter 20-12-07&Archive=Yak
>>>
>>> Text Version:
>>>
>>> http://www.matronics.com/digest/digestview.php?Style=82701&View=
txt&Chapter 20-12-07&Archive=Yak
>>>
>>>
>>> ======================
>>> EMail Version of Today's List Digest Archive
>>> ======================
>>>
>>>
>>> ----------------------------------------------------------
>>> Yak-List Digest Archive
>>> ---
>>> Total Messages Posted Mon 12/07/20: 4
>>> ----------------------------------------------------------
>>>
>>>
>>> Today's Message Index:
>>> ----------------------
>>>
>>> 1. 10:24 AM - Fw: CJ6 uneven fuel flow (Walter Lannon)
>>> 2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow (JON BLAKE)
>>> 3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow (Larry Pine)
>>> 4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow (Walter Lannon)
>>>
>>>
>>>
>>> ________________________________ Message 1 ___________________________
__________
>>>
>>>
>>> Time: 10:24:05 AM PST US
>>> From: "Walter Lannon" <wlannon@shaw.ca>
>>> Subject: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>>
>>> From: Walter Lannon
>>> Sent: Sunday, December 06, 2020 9:09 PM
>>> Subject: CJ6 uneven fuel flow
>>>
>>> Currently there is a lot of interest in the above subject on the Red
>>> Star site. Since I have some experience in this area I thought I should
>>> respond but since it will be a rather long diatribe I thought the Yak
>>> List might be a better venue.
>>>
>>> My aircraft is a 1966 model CJ6a, one of four I imported from China in
>>> 1993. Did not start my own restoration until after selling my Harvard 4
>>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
>>> including the fuel system where I found some questionable design
>>> features. During this period (from 1993) I also licensed a few others
>>> and found it was necessary to do a hot soap and water flush of the fuel
>>> vent system to remove bug debris.
>>>
>>> Many people have noted the fuel feeds from the LH tank first. That is
>>> not surprising since the LH vent system is much shorter than the RH and
>>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>>> tubing is internally clean and totally free of any damage that could
>>> restrict air flow. This is critical! There is also some minor effect
>>> favoring LH flow via the shorter fuel feed line to the header tank.
>>>
>>> The major design problem rests with the header tank flapper valves.
>>> There are three of these valves in the aircraft. One is in the fuel
>>> line from the header tank to the fuel pump. It=99s sole purpose
>>> is to direct fuel
>>> from the emerg. (wobble) pump to the engine fuel pump while preventing
>>> reverse flow back to the header tank. This is the type of function the
>>> valve is designed for and it works perfectly because there is a
>>> distinct difference in pressure on each side.
>>>
>>> With reference to the attached photos note the diameter of the flapper
>>> as compared to the diameter of the incoming fuel hole. A true
>>> =9Cflapper=9D valve is meant to open (or close) with fuel
>>> flow but pressure, though relatively small, is a factor. If we start
>>> with equal fuel one flapper will open (probably the LH). In theory as
>>> the pressure from the LH tank and the header tank is reduced at some
>>> point the RH will open and the cycle will repeat.
>>> But, in fact, the LH plus the header tank fuel is actually applying a
>>> force to the valve surface roughly double that of the smaller surface
>>> impacted by the RH fuel.
>>>
>>> I did some rough math based on tank volume and pressures, etc. and came
>>> to the following conclusion: - The major reason this system sort of
>>> works is called turbulence! If you could take off, climb and fly a trip
>>> with never a bump of any kind you will be out of gas with a full RH
>>> tank.
>>>
>>> As you probably noted I have modified the valves to allow closing
>>> pressure to impact some of the opening surface. My typical fuel
>>> imbalance is less than 5 lts. For me this is a hand filing operation
>>> (though a CNC genius could probably do it). You MUST retain a seating
>>> ring of the original closing surface. If you change that it will never
>>> close properly again due to the geometry.
>>>
>>> One of the un modified valve photos shows a Chinese character on a
>>> wrench flat. In English this reads =9CHINGE=9D and must be
>>> at the top. Improper positioning could well be the cause of serious
>>> imbalance.
>>>
>>>
>>> Cheers;
>>> Walt
>>>
>>>
>>> ________________________________ Message 2 ___________________________
__________
>>>
>>>
>>> Time: 12:28:05 PM PST US
>>> From: JON BLAKE <saber369@comcast.net>
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>> Good info Walt... many thanks.
>>>
>>> When I first bought my CJ 15 years ago, I was told to wrap the vent on t
he
>>> belly with a fine mesh screen to keep the bugs out. I was also told tha
t t
>>> he vents going out to each wing tips were installed by Yakity Yaks to he
lp
>>> prevent a bug or other debris from causing fuel starvation. Is that tru
e?
>>> Can you shed any more light on those vents?
>>>
>>>
>>> Jon Blake
>>> Saber369@comcast.net
>>>
>>> > On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>>> >
>>> >
>>> >
>>> >
>>> > From: Walter Lannon mailto:wlannon@shaw.ca
>>> > Sent: Sunday, December 06, 2020 9:09 PM
>>> > To: yaklist@matronics.com mailto:yaklist@matronics.com
>>> > Subject: CJ6 uneven fuel flow
>>> >
>>> > Currently there is a lot of interest in the above subject on the R
ed
>>> Star site. Since I have some experience in this area I thought I should
re
>>> spond but since it will be a rather long diatribe I thought the Yak List
mi
>>> ght be a better venue.
>>> >
>>> > My aircraft is a 1966 model CJ6a, one of four I imported from Chin
a i
>>> n 1993. Did not start my own restoration until after selling my Harvard
4
>>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
in
>>> cluding the fuel system where I found some questionable design features.
D
>>> uring this period (from 1993) I also licensed a few others and found it w
as
>>> necessary to do a hot soap and water flush of the fuel vent system to re
mo
>>> ve bug debris.
>>> >
>>> > Many people have noted the fuel feeds from the LH tank first. Tha
t i
>>> s not surprising since the LH vent system is much shorter than the RH a
nd
>>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>>> > tubing is internally clean and totally free of any damage that cou
ld
>>> restrict air flow. This is critical! There is also some minor effect fa
vor
>>> ing LH flow via the shorter fuel feed line to the header tank.
>>> >
>>> > The major design problem rests with the header tank flapper valves
.
>>> There are three of these valves in the aircraft. One is in the fuel lin
e f
>>> rom the header tank to the fuel pump. It=99s sole purpose is to dire
>>> ct fuel
>>> > from the emerg. (wobble) pump to the engine fuel pump while preven
tin
>>> g reverse flow back to the header tank. This is the type of function th
e v
>>> alve is designed for and it works perfectly because there is a
>>> > distinct difference in pressure on each side.
>>> >
>>> > With reference to the attached photos note the diameter of the fla
ppe
>>> r as compared to the diameter of the incoming fuel hole. A true =9Cf
>>> lapper=9D valve is meant to open (or close) with fuel flow but pressu
>>> re, though relatively small, is a factor. If we start with equal fuel o
ne
>>> flapper will open (probably the LH). In theory as the pressure from the
L
>>> H tank and the header tank is reduced at some point the RH will open and
th
>>> e cycle will repeat.
>>> > But, in fact, the LH plus the header tank fuel is actually applyin
g a
>>> force to the valve surface roughly double that of the smaller surface im
pa
>>> cted by the RH fuel.
>>> >
>>> > I did some rough math based on tank volume and pressures, etc. and
ca
>>> me to the following conclusion: - The major reason this system sort of w
ork
>>> s is called turbulence! If you could take off, climb and fly a trip wit
h n
>>> ever a bump of any kind you will be out of gas with a full RH tank.
>>> >
>>> > As you probably noted I have modified the valves to allow closing p
re
>>> ssure to impact some of the opening surface. My typical fuel imbalance i
s
>>> less than 5 lts. For me this is a hand filing operation (though a CNC g
eni
>>> us could probably do it). You MUST retain a seating ring of the origin
al
>>> closing surface. If you change that it will never close properly again d
ue
>>> to the geometry.
>>> >
>>> > One of the un modified valve photos shows a Chinese character on a
wr
>>> ench flat. In English this reads =9CHINGE=9D and must be at th
>>> e top. Improper positioning could well be the cause of serious imbalanc
e.
>>> >
>>> >
>>> > Cheers;
>>> > Walt
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>>
>>> ________________________________ Message 3 ___________________________
__________
>>>
>>>
>>> Time: 01:30:00 PM PST US
>>> From: Larry Pine <threein60@yahoo.com>
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>>
>>> Great write-up on this. Let me add a little learned knowledge to this di
scu
>>> ssion. I have no issues with what Walt stated but a few years ago I had f
ue
>>> l starvation while on the ground. I could start the engine on my electri
cal
>>> boost pump but the minute I shut it off, the engine would die. I checked
f
>>> uel levels, I removed and cleaned the fuel strainer and checked for flow
, s
>>> till nothing. Only when I removed the flapper valve under the floor, the
on
>>> e that feeds the wobble pump, I found the hinge in this flapper was worn
an
>>> d could rotate to a place where it would get stuck closed. This was the f
ir
>>> st I have ever hear of this happening. I cleaned and lightly refaced bot
h t
>>> he flapper and flapper seat. I then replaced the worn hinge pivot rod wi
th
>>> a new brass one. I have plans to take apart this valve again during this
mo
>>> nths annual and see if these is any wear taking place on the hinge rod. L
uc
>>> ky I found this on the ground but confident had this happened in flight,
my
>>> electric driven pump would have supplied enough fuel to get me back safe
ly
>>> . Still some thing that should be examined.
>>>
>>> I have bladder tanks so my vents are extended to their respective wing t
ips
>>> with a separate vent for the header tank. I find that I tend to fly more
p
>>> ressure on my left rudder because my knee board is on my right and lifti
ng
>>> my right knee a little makes writing easier. This tends to cause a notic
eab
>>> le fuel difference over a 2 hour period. I know, bad pilot bad. Very ear
ly
>>> on before I had my bladder tanks installed, I had to do an emergency div
ert
>>> because my one tank was almost dry and the opposite tank wasn't moving t
he
>>> needle yet. Only after landing I noticed the needle move. Constant fuel m
a
>>> nagement has become the norm. I optioned to not install the vent shut of
f v
>>> alues after and incident I had with another RPAer. This pilot closed one
of
>>> his vents to overcome the fuel flow difference and forgot to open the ve
nt
>>> again. On roll out with the engine pulled to ideal, the engine died on t
he
>>> runway. It would start but than die again. When we got it to parking, we
n
>>> oticed one bladder tank was sucked flat and dry..... The same side with t
he
>>> closed vent. Human factors are human factors! Unless you design a system
t
>>> o incorporate some warning when the pressure builds or the vent is close
d i
>>> ndication, this only complicates memory items that needs to be attended a
nd
>>> eventually can lead to failures.
>>>
>>> Larry Pine On Monday, December 7, 2020, 10:48:19 AM PST, Walter Lann
on
>>> <wlannon@shaw.ca> wrote:
>>>
>>> =C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020 9:09 PMT
o:
>>> yaklist@matronics.com Subject: CJ6 uneven fuel flow=C2-Currently ther
e i
>>> s a lot of interest in the above subject on the Red Star site.=C2- Sin
ce
>>> I have some experience in this area I thought I should respond but since
it
>>> will be a rather long diatribe I thought the Yak List might be a better v
e
>>> nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported from C
hi
>>> na in 1993.=C2- Did not start my own restoration until after selling m
y H
>>> arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 10
0%
>>> restoration including the fuel system where I found some questionable de
sig
>>> n features.=C2- During this period (from 1993) I also licensed a few o
the
>>> rs and found it was necessary to do a hot soap and water flush of the fu
el
>>> vent system to remove bug debris.=C2-Many people have noted the fuel f
eed
>>> s from the LH tank first.=C2- That is not surprising since the LH=C2
- v
>>> ent system is much shorter than the RH and the tube is 8 mm (6 mm ID) fo
r b
>>> oth.=C2- Not a huge problem as long as the tubing is internally clean a
nd
>>> totally free of any damage that could restrict air flow. This is critica
l!
>>> =C2- There is also some minor effect favoring LH flow via the shorter f
ue
>>> l feed line to the header tank.=C2-=C2-=C2- =C2-The major design
pr
>>> oblem rests with the header tank flapper valves.=C2- There are three o
f t
>>> hese valves in the aircraft.=C2- One is in the fuel line from the head
er
>>> tank to the fuel pump.=C2- It=99s sole purpose is to direct fuelfro
>>> m the emerg. (wobble) pump to the engine fuel pump while preventing reve
rse
>>> flow back to the header tank.=C2- This is the type of function the val
ve
>>> is designed for and it works perfectly because there is a distinct diffe
re
>>> nce in pressure on each side.=C2- =C2-With reference to the attached
ph
>>> otos note the diameter of the flapper as compared to the diameter of the
in
>>> coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
>>> open (or close) with fuel flow but pressure, though relatively small, is
a
>>> factor.=C2-=C2- If we start with equal fuel one flapper will open (p
rob
>>> ably the LH).=C2- In theory as the pressure from the LH tank and the h
ead
>>> er tank is reduced at some point the RH will open and the cycle will rep
eat
>>> .But, in fact, the LH plus the header tank fuel is actually applying a f
orc
>>> e to the valve surface roughly double that of the smaller surface impact
ed
>>> by the RH fuel.=C2-I did some rough math based on tank volume and pres
sur
>>> es, etc. and came to the following conclusion: - The major reason this s
yst
>>> em sort of works is called turbulence!=C2- If you could take off, clim
b a
>>> nd fly a trip with never a bump of any kind you will be out of gas with a
f
>>> ull RH tank. =C2-As you probably noted I have modified the valves to a
llo
>>> w closing pressure to impact some of the opening surface.=C2- My typic
al
>>> fuel imbalance is less than 5 lts.=C2- For me this is a hand filing op
era
>>> tion (though a CNC genius could probably do it).=C2-=C2- You MUST re
tai
>>> n a seating ring of the original closing surface.=C2- If you change th
at
>>> it will never close properly again due to the geometry. =C2-One of the
un
>>> modified valve photos shows a Chinese character on a wrench flat.=C2- I
n
>>> English this reads =9CHINGE=9D and must be at the top.=C2- I
>>> mproper positioning could well be the cause of serious imbalance.=C2-=
C2
>>> -Cheers;Walt=C2-=C2-=C2-=C2-=C2-
>>>
>>> ________________________________ Message 4 ___________________________
__________
>>>
>>>
>>> Time: 09:06:58 PM PST US
>>> From: "Walter Lannon" <wlannon@shaw.ca>
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>> Hi Jon;
>>> Thank you!
>>> I have never seen the wing tip vent installation but assume that was
>>> it=99s purpose. Should work as long as it terminates in a
>>> positive (or neutral) pressure area.
>>> I seem to remember from my misspent youth that Cessna produced a lightly
>>> spring loaded vent valve that was installed in the fuel cap. I have
>>> been intending to
>>> track that down for years!!!
>>> We really should have an emergency vent of some type in the CJ. ONE is
>>> not enough! In the T6/Harvard (and most aircraft) each tank is
>>> separately vented.
>>> Over the years I have seen three T6 fuel tanks where you could touch the
>>> tank bottom from the filler hole due to a plugged vent.
>>> Cheers;
>>> Walt
>>> From: JON BLAKE
>>> Sent: Monday, December 07, 2020 12:26 PM
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>> Good info Walt... many thanks.
>>> When I first bought my CJ 15 years ago, I was told to wrap the vent on
>>> the belly with a fine mesh screen to keep the bugs out. I was also told
>>> that the vents going out to each wing tips were installed by Yakity Yaks
>>> to help prevent a bug or other debris from causing fuel starvation. Is
>>> that true? Can you shed any more light on those vents?
>>>
>>>
>>> Jon Blake
>>> Saber369@comcast.net
>>>
>>> On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>>> From: Walter Lannon
>>> Sent: Sunday, December 06, 2020 9:09 PM
>>> To: yaklist@matronics.com
>>> Subject: CJ6 uneven fuel flow
>>> Currently there is a lot of interest in the above subject on the Red
>>> Star site. Since I have some experience in this area I thought I should
>>> respond but since it will be a rather long diatribe I thought the Yak
>>> List might be a better venue.
>>> My aircraft is a 1966 model CJ6a, one of four I imported from China in
>>> 1993. Did not start my own restoration until after selling my Harvard 4
>>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoration
>>> including the fuel system where I found some questionable design
>>> features. During this period (from 1993) I also licensed a few others
>>> and found it was necessary to do a hot soap and water flush of the fuel
>>> vent system to remove bug debris.
>>> Many people have noted the fuel feeds from the LH tank first. That is
>>> not surprising since the LH vent system is much shorter than the RH and
>>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>>> tubing is internally clean and totally free of any damage that could
>>> restrict air flow. This is critical! There is also some minor effect
>>> favoring LH flow via the shorter fuel feed line to the header tank.
>>> The major design problem rests with the header tank flapper valves.
>>> There are three of these valves in the aircraft. One is in the fuel
>>> line from the header tank to the fuel pump. It=99s sole purpose
>>> is to direct fuel
>>> from the emerg. (wobble) pump to the engine fuel pump while preventing
>>> reverse flow back to the header tank. This is the type of function the
>>> valve is designed for and it works perfectly because there is a
>>> distinct difference in pressure on each side.
>>> With reference to the attached photos note the diameter of the flapper
>>> as compared to the diameter of the incoming fuel hole. A true
>>> =9Cflapper=9D valve is meant to open (or close) with fuel
>>> flow but pressure, though relatively small, is a factor. If we start
>>> with equal fuel one flapper will open (probably the LH). In theory as
>>> the pressure from the LH tank and the header tank is reduced at some
>>> point the RH will open and the cycle will repeat.
>>> But, in fact, the LH plus the header tank fuel is actually applying a
>>> force to the valve surface roughly double that of the smaller surface
>>> impacted by the RH fuel.
>>> I did some rough math based on tank volume and pressures, etc. and
>>> came to the following conclusion: - The major reason this system sort of
>>> works is called turbulence! If you could take off, climb and fly a trip
>>> with never a bump of any kind you will be out of gas with a full RH
>>> tank.
>>> As you probably noted I have modified the valves to allow closing
>>> pressure to impact some of the opening surface. My typical fuel
>>> imbalance is less than 5 lts. For me this is a hand filing operation
>>> (though a CNC genius could probably do it). You MUST retain a seating
>>> ring of the original closing surface. If you change that it will never
>>> close properly again due to the geometry.
>>> One of the un modified valve photos shows a Chinese character on a
>>> wrench flat. In English this reads =9CHINGE=9D and must be
>>> at the top. Improper positioning could well be the cause of serious
>>> imbalance.
>>> Cheers;
>>> Walt
>>>
>>>
>>>
>>> ==========
>>> List" rel="noreferrer" target="_blank">http://www.matronics.com/Navi
gator?Yak-List
>>> ==========
>>> FORUMS -
>>> eferrer" target="_blank">http://forums.matronics.com
>>> ==========
>>> WIKI -
>>> errer" target="_blank">http://wiki.matronics.com
>>> ==========
>>> b Site -
>>> -Matt Dralle, List Admin.
>>> rel="noreferrer" target="_blank">http://www.matronics.com/contributi
on
>>> ==========
>>>
>>>
>>>
>>>
>
>
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
Hey Walt.
Hope everything is going well on your end. I dont use shop pressure. I use
whatever pressure is in my lungs. I blow into the hose like you're blowing
up a balloon. When you install the bladder system you put a check valve
in the vent loop behind the pilots left shoulder. That check valve keeps
air from getting to the header tank but allows fuel to escape if need be.
So when you leave one bladder open and blow into the vent on the bottom of
the plane you're only clearing the line to that tank back to the tank and
the check valve keeps the air pressure off of the header tank. The check
valve is mounted vertically with the ball closing the check valve due to
gravity and or pressure coming into the vent system through the tube out of
the bottom of the plane when it is moving.
Then I close the first bladder and then open the other one and repeat.
The system was in when I got the plane so I have no experience with the
stock system at all. Nor did I install this one. I did verify my system
is installed as the attached diagram shows. When Gil was with us he
explained the vent system was put in like this to make sure the bladders
would empty completely.
I attached the diagram for installation of the check valve as part of the
bladder system for the CJ.
Mark
N621CJ
On Tue, Dec 8, 2020 at 2:26 PM Walter Lannon <wlannon@shaw.ca> wrote:
> Hi Mark;
>
> When you =9Cblow through the system=9D are you using shop air
? If so at what
> pressure?
>
> Do you dis-connect the header tank vent line? Applying air press to the
> header will close both flappers and leave the only pressure relief to the
> fuel to engine outlet. Not sure if that will provide adequate relief.
> Your header tank may have grown a bit larger.
>
> Walt
>
> *From:* Mark Pennington <pennington.construction.inc.1@gmail.com>
> *Sent:* Tuesday, December 08, 2020 3:55 AM
> *To:* yak-list@matronics.com
> *Subject:* Re: Yak-List: Re: Yak-List Digest: 4 Msgs - 12/07/20
>
> Good Morning Yak List
>
> I fly a CJ6 with the bladders so not stock tank or vent piping.
>
> When I was having this problem I consulted another CJ owner with a bladde
r
> system ( you know who you are and thank you) and he pointed out after so
me
> photos were sent to him that my tube extending from the bottom of the pla
ne
> was most likely not long enough to be in the slipstream and apply the
> pressure to the vent system and the top of the fuel in the tanks. I
> extended the tube about 3/8" farther down and it cured my tank imbalance.
> Also, what I do about every third flight or so is I put a hose on the ven
t
> tube extending from the bottom of the plane and open one fuel tank at a
> time and blow through the system and clear the vent system back to the
> tank. I close that tank and open the other and repeat. Sometimes I can
> tell I am clearing something from the vent system back into the tank. Mo
st
> likely fuel. I dont fly straight and level very long when I go out.
>
> I make sure the ball is centered and pay attention to wings level and I
> rarely come back with a fuel imbalance. I did inspect the flapper valves
> during one of my condition inspections and made sure they were clean and
> freely moving but made no modifications to them. I usually refuel after
> the flight and before I put the plane in the hangar. Usually the tanks a
re
> within 1 to 2 gallons of each other... A couple of times, I have come ba
ck
> after a couple of hours of flight time and one tank was down much farther
> than the other. Before I put the plane away , I put the hose on the vent
> tube and could tell one tank's vent system was plugged. So the imbalance
> made sense.
>
> Hope this helps.
>
> Mark
> N621CJ
>
>
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm
_campaign=sig-email&utm_content=webmail&utm_term=icon> Virus-free.
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> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm
_campaign=sig-email&utm_content=webmail&utm_term=link>
>
> On Tue, Dec 8, 2020 at 6:20 AM Craig Payne <yakman285@gmail.com> wrote:
>
>> Some years back the popular fix was to file some notches in the flapper
>> valves. To me that seemed to defeat the purpose. Using a little MMO in t
he
>> fuel made me feel better anyway.
>>
>> Craig Payne
>>
>> On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server <
>> yak-list@matronics.com> wrote:
>>
>>> *
>>>
>>> =======================
=
>>> Online Versions of Today's List Digest Archive
>>> =======================
=
>>>
>>> Today's complete Yak-List Digest can also be found in either of the
>>> two Web Links listed below. The .html file includes the Digest
>>> formatted
>>> in HTML for viewing with a web browser and features Hyperlinked Indexes
>>> and Message Navigation. The .txt file includes the plain ASCII version
>>> of the Yak-List Digest and can be viewed with a generic text editor
>>> such as Notepad or with a web browser.
>>>
>>> HTML Version:
>>>
>>>
>>> http://www.matronics.com/digest/digestview.php?Style=82701&View=htm
l&Chapter 20-12-07&Archive=Yak
>>>
>>> Text Version:
>>>
>>>
>>> http://www.matronics.com/digest/digestview.php?Style=82701&View=txt
&Chapter 20-12-07&Archive=Yak
>>>
>>>
>>> ======================
>>> EMail Version of Today's List Digest Archive
>>> ======================
>>>
>>>
>>> ----------------------------------------------------------
>>> Yak-List Digest Archive
>>> ---
>>> Total Messages Posted Mon 12/07/20: 4
>>> ----------------------------------------------------------
>>>
>>>
>>> Today's Message Index:
>>> ----------------------
>>>
>>> 1. 10:24 AM - Fw: CJ6 uneven fuel flow (Walter Lannon)
>>> 2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow (JON BLAKE)
>>> 3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow (Larry Pine)
>>> 4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow (Walter Lannon)
>>>
>>>
>>>
>>> ________________________________ Message 1
>>> _____________________________________
>>>
>>>
>>> Time: 10:24:05 AM PST US
>>> From: "Walter Lannon" <wlannon@shaw.ca>
>>> Subject: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>>
>>> From: Walter Lannon
>>> Sent: Sunday, December 06, 2020 9:09 PM
>>> Subject: CJ6 uneven fuel flow
>>>
>>> Currently there is a lot of interest in the above subject on the Red
>>> Star site. Since I have some experience in this area I thought I shoul
d
>>> respond but since it will be a rather long diatribe I thought the Yak
>>> List might be a better venue.
>>>
>>> My aircraft is a 1966 model CJ6a, one of four I imported from China in
>>> 1993. Did not start my own restoration until after selling my Harvard
4
>>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoratio
n
>>> including the fuel system where I found some questionable design
>>> features. During this period (from 1993) I also licensed a few others
>>> and found it was necessary to do a hot soap and water flush of the fuel
>>> vent system to remove bug debris.
>>>
>>> Many people have noted the fuel feeds from the LH tank first. That is
>>> not surprising since the LH vent system is much shorter than the RH an
d
>>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>>> tubing is internally clean and totally free of any damage that could
>>> restrict air flow. This is critical! There is also some minor effect
>>> favoring LH flow via the shorter fuel feed line to the header tank.
>>>
>>> The major design problem rests with the header tank flapper valves.
>>> There are three of these valves in the aircraft. One is in the fuel
>>> line from the header tank to the fuel pump. It=99s sole purpose
>>> is to direct fuel
>>> from the emerg. (wobble) pump to the engine fuel pump while preventing
>>> reverse flow back to the header tank. This is the type of function the
>>> valve is designed for and it works perfectly because there is a
>>> distinct difference in pressure on each side.
>>>
>>> With reference to the attached photos note the diameter of the flapper
>>> as compared to the diameter of the incoming fuel hole. A true
>>> =9Cflapper=9D valve is meant to open (or close) with fuel
>>> flow but pressure, though relatively small, is a factor. If we start
>>> with equal fuel one flapper will open (probably the LH). In theory as
>>> the pressure from the LH tank and the header tank is reduced at some
>>> point the RH will open and the cycle will repeat.
>>> But, in fact, the LH plus the header tank fuel is actually applying a
>>> force to the valve surface roughly double that of the smaller surface
>>> impacted by the RH fuel.
>>>
>>> I did some rough math based on tank volume and pressures, etc. and came
>>> to the following conclusion: - The major reason this system sort of
>>> works is called turbulence! If you could take off, climb and fly a tri
p
>>> with never a bump of any kind you will be out of gas with a full RH
>>> tank.
>>>
>>> As you probably noted I have modified the valves to allow closing
>>> pressure to impact some of the opening surface. My typical fuel
>>> imbalance is less than 5 lts. For me this is a hand filing operation
>>> (though a CNC genius could probably do it). You MUST retain a seating
>>> ring of the original closing surface. If you change that it will never
>>> close properly again due to the geometry.
>>>
>>> One of the un modified valve photos shows a Chinese character on a
>>> wrench flat. In English this reads =9CHINGE=9D and must be
>>> at the top. Improper positioning could well be the cause of serious
>>> imbalance.
>>>
>>>
>>> Cheers;
>>> Walt
>>>
>>>
>>> ________________________________ Message 2
>>> _____________________________________
>>>
>>>
>>> Time: 12:28:05 PM PST US
>>> From: JON BLAKE <saber369@comcast.net>
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>> Good info Walt... many thanks.
>>>
>>> When I first bought my CJ 15 years ago, I was told to wrap the vent on
>>> the
>>> belly with a fine mesh screen to keep the bugs out. I was also told
>>> that t
>>> he vents going out to each wing tips were installed by Yakity Yaks to
>>> help
>>> prevent a bug or other debris from causing fuel starvation. Is that
>>> true?
>>> Can you shed any more light on those vents?
>>>
>>>
>>> Jon Blake
>>> Saber369@comcast.net
>>>
>>> > On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>>> >
>>> >
>>> >
>>> >
>>> > From: Walter Lannon mailto:wlannon@shaw.ca
>>> > Sent: Sunday, December 06, 2020 9:09 PM
>>> > To: yaklist@matronics.com mailto:yaklist@matronics.com
>>> > Subject: CJ6 uneven fuel flow
>>> >
>>> > Currently there is a lot of interest in the above subject on the
>>> Red
>>> Star site. Since I have some experience in this area I thought I shoul
d
>>> re
>>> spond but since it will be a rather long diatribe I thought the Yak Lis
t
>>> mi
>>> ght be a better venue.
>>> >
>>> > My aircraft is a 1966 model CJ6a, one of four I imported from
>>> China i
>>> n 1993. Did not start my own restoration until after selling my Harvar
d
>>> 4
>>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoratio
n
>>> in
>>> cluding the fuel system where I found some questionable design
>>> features. D
>>> uring this period (from 1993) I also licensed a few others and found it
>>> was
>>> necessary to do a hot soap and water flush of the fuel vent system to
>>> remo
>>> ve bug debris.
>>> >
>>> > Many people have noted the fuel feeds from the LH tank first.
>>> That i
>>> s not surprising since the LH vent system is much shorter than the RH
>>> and
>>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>>> > tubing is internally clean and totally free of any damage that
>>> could
>>> restrict air flow. This is critical! There is also some minor effect
>>> favor
>>> ing LH flow via the shorter fuel feed line to the header tank.
>>> >
>>> > The major design problem rests with the header tank flapper
>>> valves.
>>> There are three of these valves in the aircraft. One is in the fuel
>>> line f
>>> rom the header tank to the fuel pump. It=99s sole purpose is to dire
>>> ct fuel
>>> > from the emerg. (wobble) pump to the engine fuel pump while
>>> preventin
>>> g reverse flow back to the header tank. This is the type of function
>>> the v
>>> alve is designed for and it works perfectly because there is a
>>> > distinct difference in pressure on each side.
>>> >
>>> > With reference to the attached photos note the diameter of the
>>> flappe
>>> r as compared to the diameter of the incoming fuel hole. A true =9Cf
>>> lapper=9D valve is meant to open (or close) with fuel flow but pressu
>>> re, though relatively small, is a factor. If we start with equal fuel
>>> one
>>> flapper will open (probably the LH). In theory as the pressure from th
e
>>> L
>>> H tank and the header tank is reduced at some point the RH will open an
d
>>> th
>>> e cycle will repeat.
>>> > But, in fact, the LH plus the header tank fuel is actually
>>> applying a
>>> force to the valve surface roughly double that of the smaller surface
>>> impa
>>> cted by the RH fuel.
>>> >
>>> > I did some rough math based on tank volume and pressures, etc. an
d
>>> ca
>>> me to the following conclusion: - The major reason this system sort of
>>> work
>>> s is called turbulence! If you could take off, climb and fly a trip
>>> with n
>>> ever a bump of any kind you will be out of gas with a full RH tank.
>>> >
>>> > As you probably noted I have modified the valves to allow closing
>>> pre
>>> ssure to impact some of the opening surface. My typical fuel imbalance
>>> is
>>> less than 5 lts. For me this is a hand filing operation (though a CNC
>>> geni
>>> us could probably do it). You MUST retain a seating ring of the
>>> original
>>> closing surface. If you change that it will never close properly again
>>> due
>>> to the geometry.
>>> >
>>> > One of the un modified valve photos shows a Chinese character on
a
>>> wr
>>> ench flat. In English this reads =9CHINGE=9D and must be at th
>>> e top. Improper positioning could well be the cause of serious
>>> imbalance.
>>> >
>>> >
>>> > Cheers;
>>> > Walt
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>>
>>> ________________________________ Message 3
>>> _____________________________________
>>>
>>>
>>> Time: 01:30:00 PM PST US
>>> From: Larry Pine <threein60@yahoo.com>
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>>
>>> Great write-up on this. Let me add a little learned knowledge to this
>>> discu
>>> ssion. I have no issues with what Walt stated but a few years ago I had
>>> fue
>>> l starvation while on the ground. I could start the engine on my
>>> electrical
>>> boost pump but the minute I shut it off, the engine would die. I checke
d
>>> f
>>> uel levels, I removed and cleaned the fuel strainer and checked for
>>> flow, s
>>> till nothing. Only when I removed the flapper valve under the floor, th
e
>>> on
>>> e that feeds the wobble pump, I found the hinge in this flapper was wor
n
>>> an
>>> d could rotate to a place where it would get stuck closed. This was the
>>> fir
>>> st I have ever hear of this happening. I cleaned and lightly refaced
>>> both t
>>> he flapper and flapper seat. I then replaced the worn hinge pivot rod
>>> with
>>> a new brass one. I have plans to take apart this valve again during thi
s
>>> mo
>>> nths annual and see if these is any wear taking place on the hinge rod.
>>> Luc
>>> ky I found this on the ground but confident had this happened in flight
,
>>> my
>>> electric driven pump would have supplied enough fuel to get me back
>>> safely
>>> . Still some thing that should be examined.
>>>
>>> I have bladder tanks so my vents are extended to their respective wing
>>> tips
>>> with a separate vent for the header tank. I find that I tend to fly mor
e
>>> p
>>> ressure on my left rudder because my knee board is on my right and
>>> lifting
>>> my right knee a little makes writing easier. This tends to cause a
>>> noticeab
>>> le fuel difference over a 2 hour period. I know, bad pilot bad. Very
>>> early
>>> on before I had my bladder tanks installed, I had to do an emergency
>>> divert
>>> because my one tank was almost dry and the opposite tank wasn't moving
>>> the
>>> needle yet. Only after landing I noticed the needle move. Constant fuel
>>> ma
>>> nagement has become the norm. I optioned to not install the vent shut
>>> off v
>>> alues after and incident I had with another RPAer. This pilot closed on
e
>>> of
>>> his vents to overcome the fuel flow difference and forgot to open the
>>> vent
>>> again. On roll out with the engine pulled to ideal, the engine died on
>>> the
>>> runway. It would start but than die again. When we got it to parking, w
e
>>> n
>>> oticed one bladder tank was sucked flat and dry..... The same side with
>>> the
>>> closed vent. Human factors are human factors! Unless you design a syste
m
>>> t
>>> o incorporate some warning when the pressure builds or the vent is
>>> closed i
>>> ndication, this only complicates memory items that needs to be attended
>>> and
>>> eventually can lead to failures.
>>>
>>> Larry Pine On Monday, December 7, 2020, 10:48:19 AM PST, Walter
>>> Lannon
>>> <wlannon@shaw.ca> wrote:
>>>
>>> =C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020 9:09 PM
To:
>>> yaklist@matronics.com Subject: CJ6 uneven fuel flow=C2-Currently the
re
>>> i
>>> s a lot of interest in the above subject on the Red Star site.=C2- Si
nce
>>> I have some experience in this area I thought I should respond but sinc
e
>>> it
>>> will be a rather long diatribe I thought the Yak List might be a better
>>> ve
>>> nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported from
Chi
>>> na in 1993.=C2- Did not start my own restoration until after selling
my H
>>> arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 1
00%
>>> restoration including the fuel system where I found some questionable
>>> desig
>>> n features.=C2- During this period (from 1993) I also licensed a few
othe
>>> rs and found it was necessary to do a hot soap and water flush of the
>>> fuel
>>> vent system to remove bug debris.=C2-Many people have noted the fuel
feed
>>> s from the LH tank first.=C2- That is not surprising since the LH=C
2- v
>>> ent system is much shorter than the RH and the tube is 8 mm (6 mm ID)
>>> for b
>>> oth.=C2- Not a huge problem as long as the tubing is internally clean
and
>>> totally free of any damage that could restrict air flow. This is
>>> critical!
>>> =C2- There is also some minor effect favoring LH flow via the shorter
fue
>>> l feed line to the header tank.=C2-=C2-=C2- =C2-The major desig
n pr
>>> oblem rests with the header tank flapper valves.=C2- There are three
of t
>>> hese valves in the aircraft.=C2- One is in the fuel line from the hea
der
>>> tank to the fuel pump.=C2- It=99s sole purpose is to direct fuelfro
>>> m the emerg. (wobble) pump to the engine fuel pump while preventing
>>> reverse
>>> flow back to the header tank.=C2- This is the type of function the va
lve
>>> is designed for and it works perfectly because there is a distinct
>>> differe
>>> nce in pressure on each side.=C2- =C2-With reference to the attache
d ph
>>> otos note the diameter of the flapper as compared to the diameter of th
e
>>> in
>>> coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
>>> open (or close) with fuel flow but pressure, though relatively small, i
s
>>> a
>>> factor.=C2-=C2- If we start with equal fuel one flapper will open (
prob
>>> ably the LH).=C2- In theory as the pressure from the LH tank and the
head
>>> er tank is reduced at some point the RH will open and the cycle will
>>> repeat
>>> .But, in fact, the LH plus the header tank fuel is actually applying a
>>> forc
>>> e to the valve surface roughly double that of the smaller surface
>>> impacted
>>> by the RH fuel.=C2-I did some rough math based on tank volume and pre
ssur
>>> es, etc. and came to the following conclusion: - The major reason this
>>> syst
>>> em sort of works is called turbulence!=C2- If you could take off, cli
mb a
>>> nd fly a trip with never a bump of any kind you will be out of gas with
>>> a f
>>> ull RH tank. =C2-As you probably noted I have modified the valves to
allo
>>> w closing pressure to impact some of the opening surface.=C2- My typi
cal
>>> fuel imbalance is less than 5 lts.=C2- For me this is a hand filing o
pera
>>> tion (though a CNC genius could probably do it).=C2-=C2- You MUST r
etai
>>> n a seating ring of the original closing surface.=C2- If you change t
hat
>>> it will never close properly again due to the geometry. =C2-One of th
e un
>>> modified valve photos shows a Chinese character on a wrench flat.=C2-
In
>>> English this reads =9CHINGE=9D and must be at the top.=C2- I
>>> mproper positioning could well be the cause of serious imbalance.=C2-
=C2
>>> -Cheers;Walt=C2-=C2-=C2-=C2-=C2-
>>>
>>> ________________________________ Message 4
>>> _____________________________________
>>>
>>>
>>> Time: 09:06:58 PM PST US
>>> From: "Walter Lannon" <wlannon@shaw.ca>
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>> Hi Jon;
>>> Thank you!
>>> I have never seen the wing tip vent installation but assume that was
>>> it=99s purpose. Should work as long as it terminates in a
>>> positive (or neutral) pressure area.
>>> I seem to remember from my misspent youth that Cessna produced a lightl
y
>>> spring loaded vent valve that was installed in the fuel cap. I have
>>> been intending to
>>> track that down for years!!!
>>> We really should have an emergency vent of some type in the CJ. ONE is
>>> not enough! In the T6/Harvard (and most aircraft) each tank is
>>> separately vented.
>>> Over the years I have seen three T6 fuel tanks where you could touch th
e
>>> tank bottom from the filler hole due to a plugged vent.
>>> Cheers;
>>> Walt
>>> From: JON BLAKE
>>> Sent: Monday, December 07, 2020 12:26 PM
>>> Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
>>>
>>> Good info Walt... many thanks.
>>> When I first bought my CJ 15 years ago, I was told to wrap the vent on
>>> the belly with a fine mesh screen to keep the bugs out. I was also tol
d
>>> that the vents going out to each wing tips were installed by Yakity Yak
s
>>> to help prevent a bug or other debris from causing fuel starvation. Is
>>> that true? Can you shed any more light on those vents?
>>>
>>>
>>> Jon Blake
>>> Saber369@comcast.net
>>>
>>> On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
>>> From: Walter Lannon
>>> Sent: Sunday, December 06, 2020 9:09 PM
>>> To: yaklist@matronics.com
>>> Subject: CJ6 uneven fuel flow
>>> Currently there is a lot of interest in the above subject on the Red
>>> Star site. Since I have some experience in this area I thought I shoul
d
>>> respond but since it will be a rather long diatribe I thought the Yak
>>> List might be a better venue.
>>> My aircraft is a 1966 model CJ6a, one of four I imported from China i
n
>>> 1993. Did not start my own restoration until after selling my Harvard
4
>>> in 2006 (after 30 years!) It was a 6 year (off and on) 100% restoratio
n
>>> including the fuel system where I found some questionable design
>>> features. During this period (from 1993) I also licensed a few others
>>> and found it was necessary to do a hot soap and water flush of the fuel
>>> vent system to remove bug debris.
>>> Many people have noted the fuel feeds from the LH tank first. That i
s
>>> not surprising since the LH vent system is much shorter than the RH an
d
>>> the tube is 8 mm (6 mm ID) for both. Not a huge problem as long as the
>>> tubing is internally clean and totally free of any damage that could
>>> restrict air flow. This is critical! There is also some minor effect
>>> favoring LH flow via the shorter fuel feed line to the header tank.
>>> The major design problem rests with the header tank flapper valves.
>>> There are three of these valves in the aircraft. One is in the fuel
>>> line from the header tank to the fuel pump. It=99s sole purpose
>>> is to direct fuel
>>> from the emerg. (wobble) pump to the engine fuel pump while preventin
g
>>> reverse flow back to the header tank. This is the type of function the
>>> valve is designed for and it works perfectly because there is a
>>> distinct difference in pressure on each side.
>>> With reference to the attached photos note the diameter of the flappe
r
>>> as compared to the diameter of the incoming fuel hole. A true
>>> =9Cflapper=9D valve is meant to open (or close) with fuel
>>> flow but pressure, though relatively small, is a factor. If we start
>>> with equal fuel one flapper will open (probably the LH). In theory as
>>> the pressure from the LH tank and the header tank is reduced at some
>>> point the RH will open and the cycle will repeat.
>>> But, in fact, the LH plus the header tank fuel is actually applying a
>>> force to the valve surface roughly double that of the smaller surface
>>> impacted by the RH fuel.
>>> I did some rough math based on tank volume and pressures, etc. and
>>> came to the following conclusion: - The major reason this system sort o
f
>>> works is called turbulence! If you could take off, climb and fly a tri
p
>>> with never a bump of any kind you will be out of gas with a full RH
>>> tank.
>>> As you probably noted I have modified the valves to allow closing
>>> pressure to impact some of the opening surface. My typical fuel
>>> imbalance is less than 5 lts. For me this is a hand filing operation
>>> (though a CNC genius could probably do it). You MUST retain a seating
>>> ring of the original closing surface. If you change that it will never
>>> close properly again due to the geometry.
>>> One of the un modified valve photos shows a Chinese character on a
>>> wrench flat. In English this reads =9CHINGE=9D and must be
>>> at the top. Improper positioning could well be the cause of serious
>>> imbalance.
>>> Cheers;
>>> Walt
>>>
>>>
>>>
>>> ==========
>>> List" rel="noreferrer" target="_blank">
>>> http://www.matronics.com/Navigator?Yak-List
>>> ==========
>>> FORUMS -
>>> eferrer" target="_blank">http://forums.matronics.com
>>> ==========
>>> WIKI -
>>> errer" target="_blank">http://wiki.matronics.com
>>> ==========
>>> b Site -
>>> -Matt Dralle, List Admin.
>>> rel="noreferrer" target="_blank">http://www.matronics.com/contribut
ion
>>> ==========
>>>
>>>
>>>
>>>
>>>
>
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
If you use bladder tanks but didn=99t install the wing vent shutoff v
alves, this diagram won=99t work. =C2-If you vent each tank to the
wing tips=C2-instead of the cockpit, with the check valves in this config
uration, you will blow fuel out the belly vent. =C2-Because the tanks=C2
-are now=C2-at a higher pressure, the pressure is relieved through the
Hopper tank and will vent fuel out the belly vent. =C2-With the vents at
the tips, you need to turn the check valves around so=C2-air blows into t
he hopper tank, thereby pushing fuel and sucking air to fill the flow void.
=C2-With wing vent, there is no vent connection between the tanks and the
hopper.
Sent from Yahoo Mail for iPhone
On Tuesday, December 8, 2020, 13:42, Mark Pennington <pennington.constructi
on.inc.1@gmail.com> wrote:
Hey Walt.
Hope everything is going well on your end.=C2- I dont use shop pressure.
I use whatever pressure is in my lungs.=C2- I blow into the hose like you
're blowing up a balloon.=C2- =C2-When you install the bladder system y
ou put a check valve in the vent loop behind the pilots left shoulder.=C2
- That check valve keeps air from getting to the header tank but allows f
uel to escape if need be.=C2- So when you leave one bladder open and blow
into the vent on the bottom of the plane you're only clearing the line to
that tank back to the tank and the check valve keeps the air pressure off o
f the header tank.=C2- The check valve is mounted vertically with the bal
l closing the check valve due to gravity and or pressure coming into the ve
nt system through the tube out of the bottom of the plane when it is moving
.
Then I close the first bladder and then open the other one and repeat.=C2
- =C2-The system was in when I got the plane so I have no experience wi
th the stock system at all.=C2- =C2-Nor did I install this one.=C2- I
did verify my system is installed as the attached diagram shows. When Gil
was with us he explained the vent system was put in like this to make sure
the bladders would empty completely.=C2- =C2-
I attached the diagram for installation of the check valve as part=C2- of
the bladder system for the CJ.=C2-
MarkN621CJ=C2-
On Tue, Dec 8, 2020 at 2:26 PM Walter Lannon <wlannon@shaw.ca> wrote:
Hi Mark;=C2-When you =9Cblow through the system=9D are you us
ing shop air?=C2- If so at what pressure?=C2-Do you dis-connect the hea
der tank vent line?=C2-=C2- Applying air press to the header will close
both flappers and leave the only pressure relief to the fuel to engine out
let.=C2- Not sure if that will provide adequate relief.Your header tank m
ay have grown a bit larger.=C2-Walt =C2-From: Mark Pennington Sent: Tue
sday, December 08, 2020 3:55 AMTo: yak-list@matronics.com Subject: Re: Yak-
List: Re: Yak-List Digest: 4 Msgs - 12/07/20=C2-Good Morning Yak List =C2
-I fly a CJ6 with the bladders so not stock tank or vent piping.=C2-Whe
n I was having this problem I consulted another CJ owner with a bladder sys
tem ( you know who you are and thank you)=C2- and he pointed out after so
me photos were sent to him that my tube extending from the bottom of the pl
ane was most likely not long enough to be in the slipstream and apply the p
ressure to the vent system and the top of the fuel in the tanks.=C2- I ex
tended the tube about 3/8" farther down and it cured my tank imbalance.=C2
- Also, what I do about every third flight or so is I put a hose on the v
ent tube extending from the bottom of the plane and open one fuel tank at a
time and blow through the system and clear the vent system back to the tan
k.=C2- I close that tank and open the other and repeat.=C2- Sometimes I
can tell I am clearing something from the vent system back into the tank.
=C2- Most likely fuel.=C2- I dont fly straight and level very long when
I go out.=C2-=C2- =C2-I make sure the ball is centered and pay atten
tion to wings level and I rarely come back with a fuel imbalance.=C2- I d
id inspect the flapper valves during one of my condition inspections and ma
de sure they were clean and freely moving but made no modifications to them
.=C2-=C2- I usually refuel after the flight and before I put the plane
in the hangar.=C2- Usually the tanks are within 1 to 2 gallons of each ot
her... A couple of times,=C2- I have come back after a couple of hours of
flight time and one tank was down much farther than the other.=C2- Befor
e I put the plane away , I put the hose on the vent tube and could tell one
tank's vent system was plugged.=C2- So the imbalance made sense.=C2-Ho
pe this helps.=C2- =C2-MarkN621CJ=C2-=C2-=C2-=C2-
| | Virus-free. www.avast.com |
=C2-On Tue, Dec 8, 2020 at 6:20 AM Craig Payne <yakman285@gmail.com> wrot
e:
Some years back the popular fix was to file some notches in the flapper v
alves. To me that seemed to defeat the purpose. Using a little MMO in the f
uel made me feel better anyway. =C2- Craig Payne
=C2- On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server <yak-list@ma
tronics.com> wrote:
*
========================
=C2-=C2- Online Versions of Today's List Digest Archive
========================
Today's complete Yak-List Digest can also be found in either of the
two Web Links listed below.=C2- The .html file includes the Digest format
ted
in HTML for viewing with a web browser and features Hyperlinked Indexes
and Message Navigation.=C2- The .txt file includes the plain ASCII versio
n
of the Yak-List Digest and can be viewed with a generic text editor
such as Notepad or with a web browser.
HTML Version:
=C2-=C2-=C2- http://www.matronics.com/digest/digestview.php?Style=8
2701&View=html&Chapter 20-12-07&Archive=Yak
Text Version:
=C2-=C2-=C2- http://www.matronics.com/digest/digestview.php?Style=8
2701&View=txt&Chapter 20-12-07&Archive=Yak
======================
=C2-=C2- EMail Version of Today's List Digest Archive
======================
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--------------------------------------------
=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2
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=C2- Yak-List Digest Archive
=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2
-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-
=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- --
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07/20: 4
=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- --------------
--------------------------------------------
Today's Message Index:
----------------------
=C2-=C2-=C2-=C2- 1. 10:24 AM - Fw: CJ6 uneven fuel flow=C2- (Walt
er Lannon)
=C2-=C2-=C2-=C2- 2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow=C2- (
JON BLAKE)
=C2-=C2-=C2-=C2- 3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow=C2- (
Larry Pine)
=C2-=C2-=C2-=C2- 4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow=C2- (
Walter Lannon)
________________________________=C2- Message 1=C2- ____________________
_________________
Time: 10:24:05 AM PST US
From: "Walter Lannon" <wlannon@shaw.ca>
Subject: Yak-List: Fw: CJ6 uneven fuel flow
From: Walter Lannon
Sent: Sunday, December 06, 2020 9:09 PM
Subject: CJ6 uneven fuel flow
Currently there is a lot of interest in the above subject on the Red
Star site.=C2- Since I have some experience in this area I thought I shou
ld
respond but since it will be a rather long diatribe I thought the Yak
List might be a better venue.
My aircraft is a 1966 model CJ6a, one of four I imported from China in
1993.=C2- Did not start my own restoration until after selling my Harvard
4
in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 100% restorati
on
including the fuel system where I found some questionable design
features.=C2- During this period (from 1993) I also licensed a few others
and found it was necessary to do a hot soap and water flush of the fuel
vent system to remove bug debris.
Many people have noted the fuel feeds from the LH tank first.=C2- That is
not surprising since the LH=C2- vent system is much shorter than the RH a
nd
the tube is 8 mm (6 mm ID) for both.=C2- Not a huge problem as long as th
e
tubing is internally clean and totally free of any damage that could
restrict air flow. This is critical!=C2- There is also some minor effect
favoring LH flow via the shorter fuel feed line to the header tank.=C2-
=C2-=C2-
The major design problem rests with the header tank flapper valves.=C2-
There are three of these valves in the aircraft.=C2- One is in the fuel
line from the header tank to the fuel pump.=C2- It=99s sole purpose
is to direct fuel
from the emerg. (wobble) pump to the engine fuel pump while preventing
reverse flow back to the header tank.=C2- This is the type of function th
e
valve is designed for and it works perfectly because there is a
distinct difference in pressure on each side.=C2-
With reference to the attached photos note the diameter of the flapper
as compared to the diameter of the incoming fuel hole.=C2- A true
=9Cflapper=9D valve is meant to open (or close) with fuel
flow but pressure, though relatively small, is a factor.=C2-=C2- If we
start
with equal fuel one flapper will open (probably the LH).=C2- In theory as
the pressure from the LH tank and the header tank is reduced at some
point the RH will open and the cycle will repeat.
But, in fact, the LH plus the header tank fuel is actually applying a
force to the valve surface roughly double that of the smaller surface
impacted by the RH fuel.
I did some rough math based on tank volume and pressures, etc. and came
to the following conclusion: - The major reason this system sort of
works is called turbulence!=C2- If you could take off, climb and fly a tr
ip
with never a bump of any kind you will be out of gas with a full RH
tank.
As you probably noted I have modified the valves to allow closing
pressure to impact some of the opening surface.=C2- My typical fuel
imbalance is less than 5 lts.=C2- For me this is a hand filing operation
(though a CNC genius could probably do it).=C2-=C2- You MUST retain a s
eating
ring of the original closing surface.=C2- If you change that it will neve
r
close properly again due to the geometry.
One of the un modified valve photos shows a Chinese character on a
wrench flat.=C2- In English this reads =9CHINGE=9D and must be
at the top.=C2- Improper positioning could well be the cause of serious
imbalance.
Cheers;
Walt
________________________________=C2- Message 2=C2- ____________________
_________________
Time: 12:28:05 PM PST US
From: JON BLAKE <saber369@comcast.net>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Good info Walt... many thanks.=C2-
When I first bought my CJ 15 years ago, I was told to wrap the vent on the
belly with a fine mesh screen to keep the bugs out.=C2- I was also told t
hat t
he vents going out to each wing tips were installed by Yakity Yaks to help
prevent a bug or other debris from causing fuel starvation.=C2- Is that t
rue?
Can you shed any more light on those vents?
Jon Blake
Saber369@comcast.net
>=C2-=C2-=C2-=C2- On 12/07/2020 12:22 PM Walter Lannon <wlannon@sha
w.ca> wrote:
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- From: Walter Lannon mailto:wlannon@shaw.ca
>=C2-=C2-=C2-=C2- Sent: Sunday, December 06, 2020 9:09 PM
>=C2-=C2-=C2-=C2- To: yaklist@matronics.com mailto:yaklist@matronic
s.com
>=C2-=C2-=C2-=C2- Subject: CJ6 uneven fuel flow
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- Currently there is a lot of interest in the above
subject on the Red
Star site.=C2- Since I have some experience in this area I thought I shou
ld re
spond but since it will be a rather long diatribe I thought the Yak List mi
ght be a better venue.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- My aircraft is a 1966 model CJ6a, one of four I i
mported from China i
n 1993.=C2- Did not start my own restoration until after selling my Harva
rd 4
in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 100% restorati
on in
cluding the fuel system where I found some questionable design features.=C2
- D
uring this period (from 1993) I also licensed a few others and found it was
necessary to do a hot soap and water flush of the fuel vent system to remo
ve bug debris.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- Many people have noted the fuel feeds from the LH
tank first.=C2- That i
s not surprising since the LH=C2- vent system is much shorter than the RH
and
the tube is 8 mm (6 mm ID) for both.=C2- Not a huge problem as long as th
e
>=C2-=C2-=C2-=C2- tubing is internally clean and totally free of an
y damage that could
restrict air flow. This is critical!=C2- There is also some minor effect
favor
ing LH flow via the shorter fuel feed line to the header tank.=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- The major design problem rests with the header ta
nk flapper valves.=C2-
There are three of these valves in the aircraft.=C2- One is in the fuel l
ine f
rom the header tank to the fuel pump.=C2- It=99s sole purpose is to dir
e
ct fuel
>=C2-=C2-=C2-=C2- from the emerg. (wobble) pump to the engine fuel
pump while preventin
g reverse flow back to the header tank.=C2- This is the type of function
the v
alve is designed for and it works perfectly because there is a
>=C2-=C2-=C2-=C2- distinct difference in pressure on each side.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- With reference to the attached photos note the di
ameter of the flappe
r as compared to the diameter of the incoming fuel hole.=C2- A true =9C
f
lapper=9D valve is meant to open (or close) with fuel flow but pressu
re, though relatively small, is a factor.=C2-=C2- If we start with equa
l fuel one
flapper will open (probably the LH).=C2- In theory as the pressure from t
he L
H tank and the header tank is reduced at some point the RH will open and th
e cycle will repeat.
>=C2-=C2-=C2-=C2- But, in fact, the LH plus the header tank fuel is
actually applying a
force to the valve surface roughly double that of the smaller surface impa
cted by the RH fuel.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- I did some rough math based on tank volume and pr
essures, etc. and ca
me to the following conclusion: - The major reason this system sort of work
s is called turbulence!=C2- If you could take off, climb and fly a trip w
ith n
ever a bump of any kind you will be out of gas with a full RH tank.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- As you probably noted I have modified the valves
to allow closing pre
ssure to impact some of the opening surface.=C2- My typical fuel imbalanc
e is
less than 5 lts.=C2- For me this is a hand filing operation (though a CNC
geni
us could probably do it).=C2-=C2- You MUST retain a seating ring of the
original
closing surface.=C2- If you change that it will never close properly agai
n due
to the geometry.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- One of the un modified valve photos shows a Chine
se character on a wr
ench flat.=C2- In English this reads =9CHINGE=9D and must be at th
e top.=C2- Improper positioning could well be the cause of serious imbala
nce.
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2- Cheers;
>=C2-=C2-=C2-=C2- Walt
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>=C2-=C2-=C2-=C2-=C2-
>
________________________________=C2- Message 3=C2- ____________________
_________________
Time: 01:30:00 PM PST US
From: Larry Pine <threein60@yahoo.com>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Great write-up on this. Let me add a little learned knowledge to this discu
ssion. I have no issues with what Walt stated but a few years ago I had fue
l starvation while on the ground. I could start the engine on my electrical
boost pump but the minute I shut it off, the engine would die. I checked f
uel levels, I removed and cleaned the fuel strainer and checked for flow, s
till nothing. Only when I removed the flapper valve under the floor, the on
e that feeds the wobble pump, I found the hinge in this flapper was worn an
d could rotate to a place where it would get stuck closed. This was the fir
st I have ever hear of this happening. I cleaned and lightly refaced both t
he flapper and flapper seat. I then replaced the worn hinge pivot rod with
a new brass one. I have plans to take apart this valve again during this mo
nths annual and see if these is any wear taking place on the hinge rod. Luc
ky I found this on the ground but confident had this happened in flight, my
electric driven pump would have supplied enough fuel to get me back safely
. Still some thing that should be examined.
I have bladder tanks so my vents are extended to their respective wing tips
with a separate vent for the header tank. I find that I tend to fly more p
ressure on my left rudder because my knee board is on my right and lifting
my right knee a little makes writing easier. This tends to cause a noticeab
le fuel difference over a 2 hour period. I know, bad pilot bad. Very early
on before I had my bladder tanks installed, I had to do an emergency divert
because my one tank was almost dry and the opposite tank wasn't moving the
needle yet. Only after landing I noticed the needle move. Constant fuel ma
nagement has become the norm. I optioned to not install the vent shut off v
alues after and incident I had with another RPAer. This pilot closed one of
his vents to overcome the fuel flow difference and forgot to open the vent
again. On roll out with the engine pulled to ideal, the engine died on the
runway. It would start but than die again. When we got it to parking, we n
oticed one bladder tank was sucked flat and dry..... The same side with the
closed vent. Human factors are human factors! Unless you design a system t
o incorporate some warning when the pressure builds or the vent is closed i
ndication, this only complicates memory items that needs to be attended and
eventually can lead to failures.
Larry Pine=C2-=C2-=C2-=C2- On Monday, December 7, 2020, 10:48:19 AM
PST, Walter Lannon
<wlannon@shaw.ca> wrote:=C2-
=C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020 9:09 PMTo:
=C2-yaklist@matronics.com Subject: CJ6 uneven fuel flow=C2-Currently th
ere i
s a lot of interest in the above subject on the Red Star site.=C2- Since
I have some experience in this area I thought I should respond but since it
will be a rather long diatribe I thought the Yak List might be a better ve
nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported from Chi
na in 1993.=C2- Did not start my own restoration until after selling my H
arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 100%
restoration including the fuel system where I found some questionable desig
n features.=C2- During this period (from 1993) I also licensed a few othe
rs and found it was necessary to do a hot soap and water flush of the fuel
vent system to remove bug debris.=C2-Many people have noted the fuel feed
s from the LH tank first.=C2- That is not surprising since the LH=C2- v
ent system is much shorter than the RH and the tube is 8 mm (6 mm ID) for b
oth.=C2- Not a huge problem as long as the tubing is internally clean and
totally free of any damage that could restrict air flow. This is critical!
=C2- There is also some minor effect favoring LH flow via the shorter fue
l feed line to the header tank.=C2-=C2-=C2- =C2-The major design pr
oblem rests with the header tank flapper valves.=C2- There are three of t
hese valves in the aircraft.=C2- One is in the fuel line from the header
tank to the fuel pump.=C2- It=99s sole purpose is to direct fuelfro
m the emerg. (wobble) pump to the engine fuel pump while preventing reverse
flow back to the header tank.=C2- This is the type of function the valve
is designed for and it works perfectly because there is a distinct differe
nce in pressure on each side.=C2- =C2-With reference to the attached ph
otos note the diameter of the flapper as compared to the diameter of the in
coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
open (or close) with fuel flow but pressure, though relatively small, is a
factor.=C2-=C2- If we start with equal fuel one flapper will open (prob
ably the LH).=C2- In theory as the pressure from the LH tank and the head
er tank is reduced at some point the RH will open and the cycle will repeat
.But, in fact, the LH plus the header tank fuel is actually applying a forc
e to the valve surface roughly double that of the smaller surface impacted
by the RH fuel.=C2-I did some rough math based on tank volume and pressur
es, etc. and came to the following conclusion: - The major reason this syst
em sort of works is called turbulence!=C2- If you could take off, climb a
nd fly a trip with never a bump of any kind you will be out of gas with a f
ull RH tank. =C2-As you probably noted I have modified the valves to allo
w closing pressure to impact some of the opening surface.=C2- My typical
fuel imbalance is less than 5 lts.=C2- For me this is a hand filing opera
tion (though a CNC genius could probably do it).=C2-=C2- You MUST retai
n a seating ring of the original closing surface.=C2- If you change that
it will never close properly again due to the geometry. =C2-One of the un
modified valve photos shows a Chinese character on a wrench flat.=C2- In
English this reads =9CHINGE=9D and must be at the top.=C2- I
mproper positioning could well be the cause of serious imbalance.=C2-=C
2
-Cheers;Walt=C2-=C2-=C2-=C2-=C2-=C2-
________________________________=C2- Message 4=C2- ____________________
_________________
Time: 09:06:58 PM PST US
From: "Walter Lannon" <wlannon@shaw.ca>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Hi Jon;
Thank you!
I have never seen the wing tip vent installation but assume that was
it=99s purpose.=C2- Should work as long as it terminates in a
positive (or neutral) pressure area.
I seem to remember from my misspent youth that Cessna produced a lightly
spring loaded vent valve that was installed in the fuel cap.=C2- I have
been intending to
track that down for years!!!=C2-
We really should have an emergency vent of some type in the CJ.=C2- ONE i
s
not enough!=C2-=C2-=C2- In the T6/Harvard (and most aircraft) each ta
nk is
separately vented.
Over the years I have seen three T6 fuel tanks where you could touch the
tank bottom from the filler hole due to a plugged vent.
Cheers;
Walt=C2-=C2-
From: JON BLAKE
Sent: Monday, December 07, 2020 12:26 PM
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Good info Walt... many thanks.=C2-=C2-
When I first bought my CJ 15 years ago, I was told to wrap the vent on
the belly with a fine mesh screen to keep the bugs out.=C2- I was also to
ld
that the vents going out to each wing tips were installed by Yakity Yaks
to help prevent a bug or other debris from causing fuel starvation.=C2- I
s
that true?=C2- Can you shed any more light on those vents?=C2-
Jon Blake
Saber369@comcast.net
=C2- On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
=C2- From: Walter Lannon
=C2- Sent: Sunday, December 06, 2020 9:09 PM
=C2- To: yaklist@matronics.com
=C2- Subject: CJ6 uneven fuel flow
=C2- Currently there is a lot of interest in the above subject on the Red
Star site.=C2- Since I have some experience in this area I thought I shou
ld
respond but since it will be a rather long diatribe I thought the Yak
List might be a better venue.
=C2- My aircraft is a 1966 model CJ6a, one of four I imported from China
in
1993.=C2- Did not start my own restoration until after selling my Harvard
4
in 2006 (after 30 years!)=C2- It was a 6 year (off and on) 100% restorati
on
including the fuel system where I found some questionable design
features.=C2- During this period (from 1993) I also licensed a few others
and found it was necessary to do a hot soap and water flush of the fuel
vent system to remove bug debris.
=C2- Many people have noted the fuel feeds from the LH tank first.=C2-
That is
not surprising since the LH=C2- vent system is much shorter than the RH a
nd
the tube is 8 mm (6 mm ID) for both.=C2- Not a huge problem as long as th
e
=C2- tubing is internally clean and totally free of any damage that could
restrict air flow. This is critical!=C2- There is also some minor effect
favoring LH flow via the shorter fuel feed line to the header tank.=C2-
=C2-=C2-
=C2- The major design problem rests with the header tank flapper valves.
=C2-
There are three of these valves in the aircraft.=C2- One is in the fuel
line from the header tank to the fuel pump.=C2- It=99s sole purpose
is to direct fuel
=C2- from the emerg. (wobble) pump to the engine fuel pump while preventi
ng
reverse flow back to the header tank.=C2- This is the type of function th
e
valve is designed for and it works perfectly because there is a
=C2- distinct difference in pressure on each side.=C2-
=C2- With reference to the attached photos note the diameter of the flapp
er
as compared to the diameter of the incoming fuel hole.=C2- A true
=9Cflapper=9D valve is meant to open (or close) with fuel
flow but pressure, though relatively small, is a factor.=C2-=C2- If we
start
with equal fuel one flapper will open (probably the LH).=C2- In theory as
the pressure from the LH tank and the header tank is reduced at some
point the RH will open and the cycle will repeat.
=C2- But, in fact, the LH plus the header tank fuel is actually applying
a
force to the valve surface roughly double that of the smaller surface
impacted by the RH fuel.
=C2- I did some rough math based on tank volume and pressures, etc. and
came to the following conclusion: - The major reason this system sort of
works is called turbulence!=C2- If you could take off, climb and fly a tr
ip
with never a bump of any kind you will be out of gas with a full RH
tank.
=C2- As you probably noted I have modified the valves to allow closing
pressure to impact some of the opening surface.=C2- My typical fuel
imbalance is less than 5 lts.=C2- For me this is a hand filing operation
(though a CNC genius could probably do it).=C2-=C2- You MUST retain a s
eating
ring of the original closing surface.=C2- If you change that it will neve
r
close properly again due to the geometry.
=C2- One of the un modified valve photos shows a Chinese character on a
wrench flat.=C2- In English this reads =9CHINGE=9D and must be
at the top.=C2- Improper positioning could well be the cause of serious
imbalance.
=C2- Cheers;
=C2- Walt
List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigat
or?Yak-List
FORUMS -
eferrer" target="_blank">http://forums.matronics.com
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b Site -
=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- -Matt Dralle, List A
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| Subject: | Re: Yak-List Digest: 4 Msgs - 12/07/20 |
Thanks Mark;
Seems all is well. I was not aware of any details of the bladder
installation.
Cheers;
Walt
From: Mark Pennington
Sent: Tuesday, December 08, 2020 1:22 PM
Subject: Re: Yak-List: Re: Yak-List Digest: 4 Msgs - 12/07/20
Hey Walt.
Hope everything is going well on your end. I dont use shop pressure. I
use whatever pressure is in my lungs. I blow into the hose like you're
blowing up a balloon. When you install the bladder system you put a
check valve in the vent loop behind the pilots left shoulder. That
check valve keeps air from getting to the header tank but allows fuel to
escape if need be. So when you leave one bladder open and blow into the
vent on the bottom of the plane you're only clearing the line to that
tank back to the tank and the check valve keeps the air pressure off of
the header tank. The check valve is mounted vertically with the ball
closing the check valve due to gravity and or pressure coming into the
vent system through the tube out of the bottom of the plane when it is
moving.
Then I close the first bladder and then open the other one and repeat.
The system was in when I got the plane so I have no experience with the
stock system at all. Nor did I install this one. I did verify my
system is installed as the attached diagram shows. When Gil was with us
he explained the vent system was put in like this to make sure the
bladders would empty completely.
I attached the diagram for installation of the check valve as part of
the bladder system for the CJ.
Mark
N621CJ
On Tue, Dec 8, 2020 at 2:26 PM Walter Lannon <wlannon@shaw.ca> wrote:
Hi Mark;
When you =9Cblow through the system=9D are you using shop
air? If so at what pressure?
Do you dis-connect the header tank vent line? Applying air press to
the header will close both flappers and leave the only pressure relief
to the fuel to engine outlet. Not sure if that will provide adequate
relief.
Your header tank may have grown a bit larger.
Walt
From: Mark Pennington
Sent: Tuesday, December 08, 2020 3:55 AM
To: yak-list@matronics.com
Subject: Re: Yak-List: Re: Yak-List Digest: 4 Msgs - 12/07/20
Good Morning Yak List
I fly a CJ6 with the bladders so not stock tank or vent piping.
When I was having this problem I consulted another CJ owner with a
bladder system ( you know who you are and thank you) and he pointed out
after some photos were sent to him that my tube extending from the
bottom of the plane was most likely not long enough to be in the
slipstream and apply the pressure to the vent system and the top of the
fuel in the tanks. I extended the tube about 3/8" farther down and it
cured my tank imbalance. Also, what I do about every third flight or so
is I put a hose on the vent tube extending from the bottom of the plane
and open one fuel tank at a time and blow through the system and clear
the vent system back to the tank. I close that tank and open the other
and repeat. Sometimes I can tell I am clearing something from the vent
system back into the tank. Most likely fuel. I dont fly straight and
level very long when I go out.
I make sure the ball is centered and pay attention to wings level and
I rarely come back with a fuel imbalance. I did inspect the flapper
valves during one of my condition inspections and made sure they were
clean and freely moving but made no modifications to them. I usually
refuel after the flight and before I put the plane in the hangar.
Usually the tanks are within 1 to 2 gallons of each other... A couple of
times, I have come back after a couple of hours of flight time and one
tank was down much farther than the other. Before I put the plane away
, I put the hose on the vent tube and could tell one tank's vent system
was plugged. So the imbalance made sense.
Hope this helps.
Mark
N621CJ
Virus-free. www.avast.com
On Tue, Dec 8, 2020 at 6:20 AM Craig Payne <yakman285@gmail.com>
wrote:
Some years back the popular fix was to file some notches in the
flapper valves. To me that seemed to defeat the purpose. Using a little
MMO in the fuel made me feel better anyway.
Craig Payne
On Tue, Dec 8, 2020 at 2:53 AM Yak-List Digest Server
<yak-list@matronics.com> wrote:
*
Online Versions of Today's List Digest Archive
Today's complete Yak-List Digest can also be found in either of
the
two Web Links listed below. The .html file includes the Digest
formatted
in HTML for viewing with a web browser and features Hyperlinked
Indexes
and Message Navigation. The .txt file includes the plain ASCII
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of the Yak-List Digest and can be viewed with a generic text
editor
such as Notepad or with a web browser.
HTML Version:
http://www.matronics.com/digest/digestview.php?Style=82701&View=html&
Chapter 20-12-07&Archive=Yak
Text Version:
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hapter 20-12-07&Archive=Yak
======================
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======================
----------------------------------------------------------
Yak-List Digest Archive
---
Total Messages Posted Mon 12/07/20: 4
----------------------------------------------------------
Today's Message Index:
----------------------
1. 10:24 AM - Fw: CJ6 uneven fuel flow (Walter Lannon)
2. 12:28 PM - Re: Fw: CJ6 uneven fuel flow (JON BLAKE)
3. 01:30 PM - Re: Fw: CJ6 uneven fuel flow (Larry Pine)
4. 09:06 PM - Re: Fw: CJ6 uneven fuel flow (Walter Lannon)
________________________________ Message 1
_____________________________________
Time: 10:24:05 AM PST US
From: "Walter Lannon" <wlannon@shaw.ca>
Subject: Yak-List: Fw: CJ6 uneven fuel flow
From: Walter Lannon
Sent: Sunday, December 06, 2020 9:09 PM
Subject: CJ6 uneven fuel flow
Currently there is a lot of interest in the above subject on the
Red
Star site. Since I have some experience in this area I thought I
should
respond but since it will be a rather long diatribe I thought the
Yak
List might be a better venue.
My aircraft is a 1966 model CJ6a, one of four I imported from
China in
1993. Did not start my own restoration until after selling my
Harvard 4
in 2006 (after 30 years!) It was a 6 year (off and on) 100%
restoration
including the fuel system where I found some questionable design
features. During this period (from 1993) I also licensed a few
others
and found it was necessary to do a hot soap and water flush of the
fuel
vent system to remove bug debris.
Many people have noted the fuel feeds from the LH tank first.
That is
not surprising since the LH vent system is much shorter than the
RH and
the tube is 8 mm (6 mm ID) for both. Not a huge problem as long
as the
tubing is internally clean and totally free of any damage that
could
restrict air flow. This is critical! There is also some minor
effect
favoring LH flow via the shorter fuel feed line to the header
tank.
The major design problem rests with the header tank flapper
valves.
There are three of these valves in the aircraft. One is in the
fuel
line from the header tank to the fuel pump. It=99s sole purpose
is to direct fuel
from the emerg. (wobble) pump to the engine fuel pump while
preventing
reverse flow back to the header tank. This is the type of
function the
valve is designed for and it works perfectly because there is a
distinct difference in pressure on each side.
With reference to the attached photos note the diameter of the
flapper
as compared to the diameter of the incoming fuel hole. A true
=9Cflapper=9D valve is meant to open (or close) with fuel
flow but pressure, though relatively small, is a factor. If we
start
with equal fuel one flapper will open (probably the LH). In
theory as
the pressure from the LH tank and the header tank is reduced at
some
point the RH will open and the cycle will repeat.
But, in fact, the LH plus the header tank fuel is actually
applying a
force to the valve surface roughly double that of the smaller
surface
impacted by the RH fuel.
I did some rough math based on tank volume and pressures, etc. and
came
to the following conclusion: - The major reason this system sort
of
works is called turbulence! If you could take off, climb and fly
a trip
with never a bump of any kind you will be out of gas with a full
RH
tank.
As you probably noted I have modified the valves to allow closing
pressure to impact some of the opening surface. My typical fuel
imbalance is less than 5 lts. For me this is a hand filing
operation
(though a CNC genius could probably do it). You MUST retain a
seating
ring of the original closing surface. If you change that it will
never
close properly again due to the geometry.
One of the un modified valve photos shows a Chinese character on a
wrench flat. In English this reads =9CHINGE=9D and must be
at the top. Improper positioning could well be the cause of
serious
imbalance.
Cheers;
Walt
________________________________ Message 2
_____________________________________
Time: 12:28:05 PM PST US
From: JON BLAKE <saber369@comcast.net>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Good info Walt... many thanks.
When I first bought my CJ 15 years ago, I was told to wrap the
vent on the
belly with a fine mesh screen to keep the bugs out. I was also
told that t
he vents going out to each wing tips were installed by Yakity Yaks
to help
prevent a bug or other debris from causing fuel starvation. Is
that true?
Can you shed any more light on those vents?
Jon Blake
Saber369@comcast.net
> On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca>
wrote:
>
>
>
>
> From: Walter Lannon mailto:wlannon@shaw.ca
> Sent: Sunday, December 06, 2020 9:09 PM
> To: yaklist@matronics.com mailto:yaklist@matronics.com
> Subject: CJ6 uneven fuel flow
>
> Currently there is a lot of interest in the above subject on
the Red
Star site. Since I have some experience in this area I thought I
should re
spond but since it will be a rather long diatribe I thought the
Yak List mi
ght be a better venue.
>
> My aircraft is a 1966 model CJ6a, one of four I imported
from China i
n 1993. Did not start my own restoration until after selling my
Harvard 4
in 2006 (after 30 years!) It was a 6 year (off and on) 100%
restoration in
cluding the fuel system where I found some questionable design
features. D
uring this period (from 1993) I also licensed a few others and
found it was
necessary to do a hot soap and water flush of the fuel vent system
to remo
ve bug debris.
>
> Many people have noted the fuel feeds from the LH tank
first. That i
s not surprising since the LH vent system is much shorter than
the RH and
the tube is 8 mm (6 mm ID) for both. Not a huge problem as long
as the
> tubing is internally clean and totally free of any damage
that could
restrict air flow. This is critical! There is also some minor
effect favor
ing LH flow via the shorter fuel feed line to the header tank.
>
> The major design problem rests with the header tank flapper
valves.
There are three of these valves in the aircraft. One is in the
fuel line f
rom the header tank to the fuel pump. It=99s sole purpose is to
dire
ct fuel
> from the emerg. (wobble) pump to the engine fuel pump while
preventin
g reverse flow back to the header tank. This is the type of
function the v
alve is designed for and it works perfectly because there is a
> distinct difference in pressure on each side.
>
> With reference to the attached photos note the diameter of
the flappe
r as compared to the diameter of the incoming fuel hole. A true
=9Cf
lapper=9D valve is meant to open (or close) with fuel flow but
pressu
re, though relatively small, is a factor. If we start with equal
fuel one
flapper will open (probably the LH). In theory as the pressure
from the L
H tank and the header tank is reduced at some point the RH will
open and th
e cycle will repeat.
> But, in fact, the LH plus the header tank fuel is actually
applying a
force to the valve surface roughly double that of the smaller
surface impa
cted by the RH fuel.
>
> I did some rough math based on tank volume and pressures,
etc. and ca
me to the following conclusion: - The major reason this system
sort of work
s is called turbulence! If you could take off, climb and fly a
trip with n
ever a bump of any kind you will be out of gas with a full RH
tank.
>
> As you probably noted I have modified the valves to allow
closing pre
ssure to impact some of the opening surface. My typical fuel
imbalance is
less than 5 lts. For me this is a hand filing operation (though a
CNC geni
us could probably do it). You MUST retain a seating ring of the
original
closing surface. If you change that it will never close properly
again due
to the geometry.
>
> One of the un modified valve photos shows a Chinese
character on a wr
ench flat. In English this reads =9CHINGE=9D and must be at
th
e top. Improper positioning could well be the cause of serious
imbalance.
>
>
> Cheers;
> Walt
>
>
>
>
>
>
________________________________ Message 3
_____________________________________
Time: 01:30:00 PM PST US
From: Larry Pine <threein60@yahoo.com>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Great write-up on this. Let me add a little learned knowledge to
this discu
ssion. I have no issues with what Walt stated but a few years ago
I had fue
l starvation while on the ground. I could start the engine on my
electrical
boost pump but the minute I shut it off, the engine would die. I
checked f
uel levels, I removed and cleaned the fuel strainer and checked
for flow, s
till nothing. Only when I removed the flapper valve under the
floor, the on
e that feeds the wobble pump, I found the hinge in this flapper
was worn an
d could rotate to a place where it would get stuck closed. This
was the fir
st I have ever hear of this happening. I cleaned and lightly
refaced both t
he flapper and flapper seat. I then replaced the worn hinge pivot
rod with
a new brass one. I have plans to take apart this valve again
during this mo
nths annual and see if these is any wear taking place on the hinge
rod. Luc
ky I found this on the ground but confident had this happened in
flight, my
electric driven pump would have supplied enough fuel to get me
back safely
. Still some thing that should be examined.
I have bladder tanks so my vents are extended to their respective
wing tips
with a separate vent for the header tank. I find that I tend to
fly more p
ressure on my left rudder because my knee board is on my right and
lifting
my right knee a little makes writing easier. This tends to cause a
noticeab
le fuel difference over a 2 hour period. I know, bad pilot bad.
Very early
on before I had my bladder tanks installed, I had to do an
emergency divert
because my one tank was almost dry and the opposite tank wasn't
moving the
needle yet. Only after landing I noticed the needle move. Constant
fuel ma
nagement has become the norm. I optioned to not install the vent
shut off v
alues after and incident I had with another RPAer. This pilot
closed one of
his vents to overcome the fuel flow difference and forgot to open
the vent
again. On roll out with the engine pulled to ideal, the engine
died on the
runway. It would start but than die again. When we got it to
parking, we n
oticed one bladder tank was sucked flat and dry..... The same side
with the
closed vent. Human factors are human factors! Unless you design a
system t
o incorporate some warning when the pressure builds or the vent is
closed i
ndication, this only complicates memory items that needs to be
attended and
eventually can lead to failures.
Larry Pine On Monday, December 7, 2020, 10:48:19 AM PST,
Walter Lannon
<wlannon@shaw.ca> wrote:
=C2-=C2-From: Walter Lannon Sent: Sunday, December 06, 2020
9:09 PMTo:
yaklist@matronics.com Subject: CJ6 uneven fuel
flow=C2-Currently there i
s a lot of interest in the above subject on the Red Star
site.=C2- Since
I have some experience in this area I thought I should respond but
since it
will be a rather long diatribe I thought the Yak List might be a
better ve
nue.=C2-My aircraft is a 1966 model CJ6a, one of four I imported
from Chi
na in 1993.=C2- Did not start my own restoration until after
selling my H
arvard 4 in 2006 (after 30 years!)=C2- It was a 6 year (off and
on) 100%
restoration including the fuel system where I found some
questionable desig
n features.=C2- During this period (from 1993) I also licensed a
few othe
rs and found it was necessary to do a hot soap and water flush of
the fuel
vent system to remove bug debris.=C2-Many people have noted the
fuel feed
s from the LH tank first.=C2- That is not surprising since the
LH=C2- v
ent system is much shorter than the RH and the tube is 8 mm (6 mm
ID) for b
oth.=C2- Not a huge problem as long as the tubing is internally
clean and
totally free of any damage that could restrict air flow. This is
critical!
=C2- There is also some minor effect favoring LH flow via the
shorter fue
l feed line to the header tank.=C2-=C2-=C2- =C2-The major
design pr
oblem rests with the header tank flapper valves.=C2- There are
three of t
hese valves in the aircraft.=C2- One is in the fuel line from
the header
tank to the fuel pump.=C2- It=99s sole purpose is to direct
fuelfro
m the emerg. (wobble) pump to the engine fuel pump while
preventing reverse
flow back to the header tank.=C2- This is the type of function
the valve
is designed for and it works perfectly because there is a distinct
differe
nce in pressure on each side.=C2- =C2-With reference to the
attached ph
otos note the diameter of the flapper as compared to the diameter
of the in
coming fuel hole.=C2- A true =9Cflapper=9D valve is meant to
open (or close) with fuel flow but pressure, though relatively
small, is a
factor.=C2-=C2- If we start with equal fuel one flapper will
open (prob
ably the LH).=C2- In theory as the pressure from the LH tank and
the head
er tank is reduced at some point the RH will open and the cycle
will repeat
.But, in fact, the LH plus the header tank fuel is actually
applying a forc
e to the valve surface roughly double that of the smaller surface
impacted
by the RH fuel.=C2-I did some rough math based on tank volume
and pressur
es, etc. and came to the following conclusion: - The major reason
this syst
em sort of works is called turbulence!=C2- If you could take
off, climb a
nd fly a trip with never a bump of any kind you will be out of gas
with a f
ull RH tank. =C2-As you probably noted I have modified the
valves to allo
w closing pressure to impact some of the opening surface.=C2- My
typical
fuel imbalance is less than 5 lts.=C2- For me this is a hand
filing opera
tion (though a CNC genius could probably do it).=C2-=C2- You
MUST retai
n a seating ring of the original closing surface.=C2- If you
change that
it will never close properly again due to the geometry. =C2-One
of the un
modified valve photos shows a Chinese character on a wrench
flat.=C2- In
English this reads =9CHINGE=9D and must be at the top.=C2- I
mproper positioning could well be the cause of serious
imbalance.=C2-=C2
-Cheers;Walt=C2-=C2-=C2-=C2-=C2-
________________________________ Message 4
_____________________________________
Time: 09:06:58 PM PST US
From: "Walter Lannon" <wlannon@shaw.ca>
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Hi Jon;
Thank you!
I have never seen the wing tip vent installation but assume that
was
it=99s purpose. Should work as long as it terminates in a
positive (or neutral) pressure area.
I seem to remember from my misspent youth that Cessna produced a
lightly
spring loaded vent valve that was installed in the fuel cap. I
have
been intending to
track that down for years!!!
We really should have an emergency vent of some type in the CJ.
ONE is
not enough! In the T6/Harvard (and most aircraft) each tank is
separately vented.
Over the years I have seen three T6 fuel tanks where you could
touch the
tank bottom from the filler hole due to a plugged vent.
Cheers;
Walt
From: JON BLAKE
Sent: Monday, December 07, 2020 12:26 PM
Subject: Re: Yak-List: Fw: CJ6 uneven fuel flow
Good info Walt... many thanks.
When I first bought my CJ 15 years ago, I was told to wrap the
vent on
the belly with a fine mesh screen to keep the bugs out. I was
also told
that the vents going out to each wing tips were installed by
Yakity Yaks
to help prevent a bug or other debris from causing fuel
starvation. Is
that true? Can you shed any more light on those vents?
Jon Blake
Saber369@comcast.net
On 12/07/2020 12:22 PM Walter Lannon <wlannon@shaw.ca> wrote:
From: Walter Lannon
Sent: Sunday, December 06, 2020 9:09 PM
To: yaklist@matronics.com
Subject: CJ6 uneven fuel flow
Currently there is a lot of interest in the above subject on the
Red
Star site. Since I have some experience in this area I thought I
should
respond but since it will be a rather long diatribe I thought the
Yak
List might be a better venue.
My aircraft is a 1966 model CJ6a, one of four I imported from
China in
1993. Did not start my own restoration until after selling my
Harvard 4
in 2006 (after 30 years!) It was a 6 year (off and on) 100%
restoration
including the fuel system where I found some questionable design
features. During this period (from 1993) I also licensed a few
others
and found it was necessary to do a hot soap and water flush of the
fuel
vent system to remove bug debris.
Many people have noted the fuel feeds from the LH tank first.
That is
not surprising since the LH vent system is much shorter than the
RH and
the tube is 8 mm (6 mm ID) for both. Not a huge problem as long
as the
tubing is internally clean and totally free of any damage that
could
restrict air flow. This is critical! There is also some minor
effect
favoring LH flow via the shorter fuel feed line to the header
tank.
The major design problem rests with the header tank flapper
valves.
There are three of these valves in the aircraft. One is in the
fuel
line from the header tank to the fuel pump. It=99s sole purpose
is to direct fuel
from the emerg. (wobble) pump to the engine fuel pump while
preventing
reverse flow back to the header tank. This is the type of
function the
valve is designed for and it works perfectly because there is a
distinct difference in pressure on each side.
With reference to the attached photos note the diameter of the
flapper
as compared to the diameter of the incoming fuel hole. A true
=9Cflapper=9D valve is meant to open (or close) with fuel
flow but pressure, though relatively small, is a factor. If we
start
with equal fuel one flapper will open (probably the LH). In
theory as
the pressure from the LH tank and the header tank is reduced at
some
point the RH will open and the cycle will repeat.
But, in fact, the LH plus the header tank fuel is actually
applying a
force to the valve surface roughly double that of the smaller
surface
impacted by the RH fuel.
I did some rough math based on tank volume and pressures, etc.
and
came to the following conclusion: - The major reason this system
sort of
works is called turbulence! If you could take off, climb and fly
a trip
with never a bump of any kind you will be out of gas with a full
RH
tank.
As you probably noted I have modified the valves to allow
closing
pressure to impact some of the opening surface. My typical fuel
imbalance is less than 5 lts. For me this is a hand filing
operation
(though a CNC genius could probably do it). You MUST retain a
seating
ring of the original closing surface. If you change that it will
never
close properly again due to the geometry.
One of the un modified valve photos shows a Chinese character on
a
wrench flat. In English this reads =9CHINGE=9D and must be
at the top. Improper positioning could well be the cause of
serious
imbalance.
Cheers;
Walt
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