Today's Message Index:
----------------------
1. 01:17 AM - Re: Re: Fuel return line (David Joyce)
2. 01:51 AM - Re: Fuel return line (Alan Carter)
3. 07:29 AM - Re: Re: Fuel return line (GRAHAM SINGLETON)
4. 10:36 AM - Re: Re: Fuel return line (Kevin Klinefelter)
5. 11:04 AM - Re: Re: Fuel return line (Sacha)
6. 11:36 AM - Re: Re: Fuel return line (FLYaDIVE)
7. 12:48 PM - Re: Fuel return line (Alan Carter)
8. 01:52 PM - Re: Re: Fuel return line (GRAHAM SINGLETON)
9. 05:14 PM - Re: Fuel return line (Roger Lee)
Message 1
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| Subject: | Re: Fuel return line |
Bob, I strongly suspect that altitude is of no great
consequence, certainly compared with fuel temperature
issues. With my 914 I have flown round the upper regions
of the Alps on Mogas with no problem , and it is striking
that all Austrian Rotax planes seem to use the Mogas which
is available on virtually every Austrian airfield, (and I
think I have been told that their CAA does not impose a
height limit). The few instances of what I have diagnosed
as vapour lock, that I have experienced have all been at
low level in hot weather shortly after take off after
stopping for lunch, when the plane has been sitting out in
the sun, and under cowl temps have been very high.
Regards, David Joyce, G-XSDJ
On Mon, 8 Apr 2013 07:31:53 +0100
"Bob Harrison" <ptag.dev@tiscali.co.uk> wrote:
><ptag.dev@tiscali.co.uk>
>
> Hi! Alan/all
> The Jabiru incident to which I refer was with their
>engine mounted fuel pump
> plus another electrical pick up pump.
> But of course in my ultimate bad dream, actually a
>nightmare! The Jabiru
> 3300 I had fitted was never without overheating problems
>...... then take it
> up on Mogas in a stinking hot summer day to about
>5,000ft and it lets you
> know the limits of using Mogas. With the 914 Rotax I
>would never fly hot and
> high with Mogas, I think the recommended limits are
>about 2,000ft and 20deg
> C Ambient but having said that someone more clever than
>me will likely
> correct me !
> But the 914 on 100ll and two electrical pumps took me
>safely to 17,500ft
> over Mont Blanc with Ivor Phillips as a "two ship" last
>August. Outside
> ambient at that height was approx 4deg C but at -2deg\C
>per 1000ft the
> ambient at ground was very hot. (as an aside had the
>Jabiru been the
> "donkey" it used to struggle at less than 50ft per
>minute climb at 13,000ft
> like "watching paint dry" even without vaporisation !)
> Sorry about that
> chaps I couldn't refrain any longer !
> Bob Harrison. G-PTAG
>
> -----Original Message-----
>From: owner-rotaxengines-list-server@matronics.com
> [mailto:owner-rotaxengines-list-server@matronics.com] On
>Behalf Of Alan
> Carter
> Sent: 07 April 2013 22:55
> To: rotaxengines-list@matronics.com
> Subject: RotaxEngines-List: Re: Fuel return line
>
> --> <alancarteresq@onetel.net>
>
> Hi All.
> My 914 has two fuel pumps, one pump has to run all the
>time as i think the
> 914 has no engine drive pump, Why?
> These pumps are mounted well away from the engine in the
>belly of the
> fuselage, so cooling of the pumps is good, Has there
>been any problems with
> vapor lock on the 914, using Mogas.
> Alan
>
>
>
>
>
>
>Un/Subscription,
>http://www.matronics.com/Navigator?RotaxEngines-List
>Forums!
>Admin.
>
>
>
Message 2
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| Subject: | Re: Fuel return line |
Hi All.
Wow 17500 ft over mountains, you chaps must have God on your side.
The 914 totally reliant on Electricity, wants a little generator to pop out the
side as a back up.
My concern is Ethanol, have posted before on this subject.
But could somebody sent me a private email on what's at the garage for flying in
the UK and only at UK temperature. ie private e-mail only.
Alan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=398122#398122
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| Subject: | Re: Fuel return line |
=C2-Sacha=0Aall sounds reasonable to me, I would just add that low pressu
re caused by suction from the pump(s) could cause vaporization too. =0AI on
ce had low fuel pressure because there was a minute leak upstream of the el
ectric pump and at low tank contents it=0Asucked air in.=0Ano end to the va
riety of gotchas out there is there?=0AGraham=0A=0A=0A=0A=0A_______________
_________________=0A From: Sacha <uuccio@gmail.com>=0ATo: rotaxengines-list
@matronics.com =0ASent: Sunday, 7 April 2013, 23:38=0ASubject: RE: RotaxEng
ines-List: Re: Fuel return line=0A =0A=0ABarry/Graham/Roger,=0AI=99m
no expert, but I=99m going to try and summarize the arguments here.
=C2- There is no question that Vapour Lock does occur and that it can be
a serious problem.=C2- I plan to fly in a hot climate with mountainous te
rrain (i.e. at altitude), hence my concern.=0ATo summarize what I=99m
hearing:=0A-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- High fuel tem
p is bad because is causes fuel to vaporize easily (so don=99t shut d
own your engine suddenly and then try to restart it without cooling it as t
he fuel lines will likely be heat soaked)=0A-=C2-=C2-=C2-=C2-=C2-
=C2-=C2-=C2- High fuel pressure is good to the extent that =0Ao=C2-
a) it increases the temp at which fuel vaporizes (though IMO this effect w
ould be marginal as the Vaporization Temp varies as 1/log Pressure) and =0A
o=C2- b) if a fuel return line is fitted, the fuel pump mixes the warmer
fuel in the lines under the cowling with cooler fuel from the fuel tanks/ga
scolator (unless you left your plane out in the sun and your wings are pain
ted in a dark colour in which case fuel in your=C2- tanks might be quite
warm?).=0A-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- Very high fuel
pressure is bad because it can cause the carbs to flood, hence the advisabi
lity of fitting a fuel return line=0A=C2-=0AIf one encounters vapour lock
during flight, what is the best way of dealing with it, assuming one has s
ufficient altitude? Reduce throttle and descent at a decent airspeed to coo
l the engine?=0ASacha=0A=C2-=0A=C2-=0A=C2-=0A=C2-=0AFrom:owner-rota
xengines-list-server@matronics.com [mailto:owner-rotaxengines-list-server@m
atronics.com] On Behalf Of GRAHAM SINGLETON=0ASent: Sunday, 07 April, 2013
22:25=0ATo: rotaxengines-list@matronics.com=0ASubject: Re: RotaxEngines-Lis
t: Re: Fuel return line=0A=C2-=0AVapour lock certainly does occur. I know
of several instances, one of which resulted in a written off aircraft. It
happens when the=C2-=0Aengine driven fuel pump=C2-gets heated=C2-by
=C2-the engine oil and then heats the fuel. Low fuel flow rate such as
=C2-when=C2-taxiing or waiting for air traffic on the ground=0Acan vapo
rize the fuel, especially Mogas.=C2-The fuel return =C2-Rotax recommend
keeps more fuel flowing through the system which=C2-helps=C2-cool the
pump and ensures cold fuel when you need it for high power.=C2-=0AMost=C2
-carburetor=C2-installations in cars have a fuel=C2-return=C2-line
for the same reasons.=0AGraham=0A=0A________________________________=0A=0AF
rom:FLYaDIVE <flyadive@gmail.com>=0ATo: rotaxengines-list@matronics.com =0A
Sent: Sunday, 7 April 2013, 19:08=0ASubject: Re: RotaxEngines-List: Re: Fue
l return line=0A=C2-=0ASacha:=0A=C2-=0AYou have some great thought prov
oking questions. =C2-I hope some are provoked.=0AFire sleeves or One piec
e Molded Teflon fuel lines are the way to go.=0AYou always want to do all y
ou can to keep extra heat from fuel and oil lines.=0ABUT! =C2-Where did t
his Old Wives Tail of Vapor Lock come from? =C2-It is a BUNCH OF BUNK!=0A
The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING t
o prevent Vapor Lock. =C2-Well, almost nothing - It corrects Pilot/Builde
r error.=0AVapor Lock happens ON THE GROUND and is=C2-experienced usually
at start up and sometimes in the air,=C2-immediately=C2-during or afte
r rotation.=0AVapor Lock can occur with MoGAs or AvGas.=0AIt is more of a P
OOR PILOT SHUTDOWN PROCEDURE that anything else.=0AAnd since we are talking
Home Built Planes and=C2-Self Proclaimed=C2-Engineers - - Builder erro
r.=0ASo, what does the "T" fitting do? =C2-Well, the history goes way bac
k to the 1960's... =C2-Electric home made Fuel Pumps were being used on
=C2-Carbureted=C2-engines. And the engines were FLOODING like crazy.
=C2-Flooding, Fires, Poor=C2-Starts (if at all), =C2-Dying=C2-when
the throttle was floored and Low HP. =C2-All because of TOO MUCH Fuel Pre
ssure Pushing the=C2-Carburetor's=C2-intake valve off the seat and floo
ding the carb.=C2-=0ASo, how do you get more fuel to the carb so it does
not go LEAN? =C2-You do a whole lot of pressure testing and engineering
=C2-- BUT! =C2-These were HOME MADE FUEL PUMPS - And Manufacturer made
Carbs. =C2-Transducers=C2-were not around then. =C2-It was too costly
to try to figure out how many GPH and How much Fuel Pressure would work,an
d what size spring to use... =C2-Too many variables.=0AThe QUICK and EASY
and VERY=C2-Effective=C2-solution... =C2-Put a "T" fitting in the li
ne and the excess pressure and excess fuel is returned to the fuel tank.=0A
The Carb takes what it needs - Has a steady supply of fuel and does NOT go
lean no=C2-matter=C2-how fast you hit the throttle.=0ANo Smoke and Mirr
ors, No=C2-ridiculous Vapor Lock=C2-theories. =C2-But, hell, this is
aviation so everybody just re-invents the wheel with their own ideas. =C2
-=0A=C2-=0AI=0A=C2-=0A=C2-=0Ahttp://www.matronics.com/Navigator?Rot
axEngines-List=0Ahttp://forums.matronics.com=0Ahttp://www.matronics.com/con
=========================0A
=======================
Message 4
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| Subject: | Re: Fuel return line |
I operate the 914/Airmaster powered Europa regularly from high desert and cruise
at 17500' over the mountains of the western US burning 91 auto gas ( up to 10%
ethanol) with no problems.
Kevin
On Apr 8, 2013, at 1:16 AM, "David Joyce" <davidjoyce@doctors.org.uk> wrote:
>
>
> Bob, I strongly suspect that altitude is of no great consequence, certainly compared
with fuel temperature issues. With my 914 I have flown round the upper
regions of the Alps on Mogas with no problem , and it is striking that all Austrian
Rotax planes seem to use the Mogas which is available on virtually every
Austrian airfield, (and I think I have been told that their CAA does not impose
a height limit). The few instances of what I have diagnosed as vapour lock,
that I have experienced have all been at low level in hot weather shortly after
take off after stopping for lunch, when the plane has been sitting out in
the sun, and under cowl temps have been very high.
> Regards, David Joyce, G-XSDJ
>
> On Mon, 8 Apr 2013 07:31:53 +0100
> "Bob Harrison" <ptag.dev@tiscali.co.uk> wrote:
>> Hi! Alan/all
>> The Jabiru incident to which I refer was with their engine mounted fuel pump
>> plus another electrical pick up pump.
>> But of course in my ultimate bad dream, actually a nightmare! The Jabiru
>> 3300 I had fitted was never without overheating problems ...... then take it
>> up on Mogas in a stinking hot summer day to about 5,000ft and it lets you
>> know the limits of using Mogas. With the 914 Rotax I would never fly hot and
>> high with Mogas, I think the recommended limits are about 2,000ft and 20deg
>> C Ambient but having said that someone more clever than me will likely
>> correct me !
>> But the 914 on 100ll and two electrical pumps took me safely to 17,500ft
>> over Mont Blanc with Ivor Phillips as a "two ship" last August. Outside
>> ambient at that height was approx 4deg C but at -2deg\C per 1000ft the
>> ambient at ground was very hot. (as an aside had the Jabiru been the
>> "donkey" it used to struggle at less than 50ft per minute climb at 13,000ft
>> like "watching paint dry" even without vaporisation !) Sorry about that
>> chaps I couldn't refrain any longer ! Bob Harrison. G-PTAG
>> -----Original Message-----
>> From: owner-rotaxengines-list-server@matronics.com
>> [mailto:owner-rotaxengines-list-server@matronics.com] On Behalf Of Alan
>> Carter
>> Sent: 07 April 2013 22:55
>> To: rotaxengines-list@matronics.com
>> Subject: RotaxEngines-List: Re: Fuel return line
>> Hi All.
>> My 914 has two fuel pumps, one pump has to run all the time as i think the
>> 914 has no engine drive pump, Why?
>> These pumps are mounted well away from the engine in the belly of the
>> fuselage, so cooling of the pumps is good, Has there been any problems with
>> vapor lock on the 914, using Mogas.
>> Alan
>> Un/Subscription,
>> http://www.matronics.com/Navigator?RotaxEngines-List
>> Forums!
>> Admin.
>
>
>
>
Message 5
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| Subject: | Re: Fuel return line |
Graham,
Interesting, I hadn=99t thought of that one :)
Another question (tell me if this is boring you): has anyone had
experience of vapour lock and then been able to successfully restart the
engine in flight? What steps were taken?
Sacha
From: owner-rotaxengines-list-server@matronics.com
[mailto:owner-rotaxengines-list-server@matronics.com] On Behalf Of
GRAHAM SINGLETON
Sent: Monday, 08 April, 2013 15:29
Subject: Re: RotaxEngines-List: Re: Fuel return line
Sacha
all sounds reasonable to me, I would just add that low pressure caused
by suction from the pump(s) could cause vaporization too.
I once had low fuel pressure because there was a minute leak upstream of
the electric pump and at low tank contents it
sucked air in.
no end to the variety of gotchas out there is there?
Graham
Message 6
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| Subject: | Re: Fuel return line |
Graham:
You have identified yourself as a creator of myths and a woman of Old
Wife's Tales. Let's take each of your statements:
" I know of several instances, one of which resulted in a written off
aircraft. It happens when the engine driven fuel pump gets heated by the
engine oil and then heats the fuel." I'm sure there was more to it, but...
That sure sounds like poor design/construction. ALL Lycoming
and Continental engines have a mechanical fuel pump mounted directly to the
engine case; why don't they have this mythical Vapor Lock ever warm day?
YES - ALL engines take the chance of Vapor Lock, but, it is things like
aluminum fuel lines, TEFLON fuel lines and Fire Sleeves that prevent it.
And more so proper handling by the pilot/builder.
I have flown 5 planes on MoGas over a 12 year period and NEVER had Vapor
Lock. Yes, in the summer's of the Mid Atlantic I also caused Vapor Lock
in a C-172 using AvGas, just to prove it can be done. Of course on the
ground and it was done after an improper shutdown and inproper restart.
Vapor Lock - CANNOT be created when there is fuel flow. As long as the
fuel is flowing it is not expanding. It MUST happen at shut down. UNLESS
- as I said some very poor building practices were followed, which ran a
fuel line next to or above a hot point such as an exhaust pipe. I'm trying
to believe that even if the builder made that mistake the DAR would have
caught it. AND isn't this the supposed purpose of installing the "T"
fitting.
Vapor Lock requires two things:
1 - The fuel to be heated allowing it to expand and
2 - A place for the expanded gas (VAPOR) to be TRAPPED.
Such a Up or Down U bend or a pig-tail.
End of your first myth .
Second myth: "The fuel return Rotax recommend keeps more fuel flowing
through the system which helps cool the pump and ensures cold fuel when you
need it for high power." Where to begin with this one, it is equivalent to
cleaning the Augean Stables.
Part A: If you have two pumps in series Pump X and Pump Y. And Pump X
comes from the tank and Pump Y feeds into the carb. And Pump X feeds at 10
PSI and 10 GPH and Pump Y Pushes at 12 PSI and 12 GPH what do you think
will happen in the connection between the two pumps?
Since Pump Y requires/displaces more fuel than Pump X can deliver there
will be a LOSS of fuel between the two... To the untrained eye that may
look like a Vapor Lock but it is just Fuel Starvation. That is why you
place the HIGHER supplying pump (Pump X) before the lower supplying pump
(Pump Y). You can always reduce what you have - You can't reduce what you
don't have.
Part B: If there you have fuel at Zero Deg F and it is not flowing through
the pump there is NO cooling taking place. Sure there is some conduction
BUT the mass of the fuel pump Vs the mass of the fuel in the fuel line and
the line itself is NOT worth considering. Ah, but I just did, just in case
you use Machiavellian Logic. What kind of fuel lines are people using?
Part C: Let's use some of this ridiculous logic that is
being spewed forth... Let's say you have a really terrible cooling system
on your plane and through the use of this Magic "T" fitting the Hot fuel is
being returned to the tank. What about the fuel that is in the line
between the electric fuel pump and the mechanical fuel pump of the HOT
engine? Why isn't that causing Vapor Lock? Then again it may? All
dependent on how well the builder did their job.
Questions: How many are using TYGON fuel lines? How many are
using some-other plastic fuel line?
Third myth: "Most carburetor installations in cars have a fuel return line
for the same reasons." Most old carbureted cars NEVER had a fuel return
line. As I stated before, when electric fuel pumps came into play they
needed a method of increasing fuel flow without flooding the carb,
therefore "T" fittings and fuel return lines. Fuel return lines came into
play NOT because of Vapor Lock but because of:
a> The EPA - They did not want gas fumes evaporating into the atmosphere.
b> This was first fought by the car manufactures but later was proven to be
helpful BECAUSE they were able to brag (advertise) about an INCREASE in
gas mileage... Not really true - But just that you had more gas in you tank
due to less evaporation. How much more? Ask the EPA!
Today all cars have return lines and pressure gas caps and many have fuel
injection. So if one wants to use Machiavellian Logic here again - - - It
was because of Vapor Lock. NOT!
A Vapor Lock is the Void between a myth being trapped in the mind and the
truth trying to replace it.
Barry
Hey, I'm 7 days late but: Did you know you have to do a New W&B if you
change from AvGas to MoGas because MoGas does not have Lead!
On Sun, Apr 7, 2013 at 5:25 PM, GRAHAM SINGLETON <
grahamsingleton@btinternet.com> wrote:
> Vapour lock certainly does occur. I know of several instances, one of
> which resulted in a written off aircraft. It happens when the engine
> driven fuel pump gets heated by the engine oil and then heats the fuel. Low
> fuel flow rate such as when taxiing or waiting for air traffic on the
> ground can vaporize the fuel, especially Mogas. The fuel return Rotax
> recommend keeps more fuel flowing through the system which helps cool the
> pump and ensures cold fuel when you need it for high power.
> Most carburetor installations in cars have a fuel return line for the same
> reasons.
> Graham
> ------------------------------
> *From:* FLYaDIVE <flyadive@gmail.com>
> *To:* rotaxengines-list@matronics.com
> *Sent:* Sunday, 7 April 2013, 19:08
> *Subject:* Re: RotaxEngines-List: Re: Fuel return line
>
> Sacha:
>
> You have some great thought provoking questions. I hope some are provoked.
> Fire sleeves or One piece Molded Teflon fuel lines are the way to go.
> You always want to do all you can to keep extra heat from fuel and oil
> lines.
> BUT! Where did this Old Wives Tail of Vapor Lock come from? It is a
> BUNCH OF BUNK!
> The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING
> to prevent Vapor Lock. Well, almost nothing - It corrects Pilot/Builder
> error.
> Vapor Lock happens ON THE GROUND and is experienced usually at start up
> and sometimes in the air, immediately during or after rotation.
> Vapor Lock can occur with MoGAs or AvGas.
> It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.
> And since we are talking Home Built Planes and Self Proclaimed Engineers -
> - Builder error.
> So, what does the "T" fitting do? Well, the history goes way back to the
> 1960's... Electric home made Fuel Pumps were being used
> on Carbureted engines. And the engines were FLOODING like crazy. Flooding,
> Fires, Poor Starts (if at all), Dying when the throttle was floored and
> Low HP. All because of TOO MUCH Fuel Pressure Pushing
> the Carburetor's intake valve off the seat and flooding the carb.
> So, how do you get more fuel to the carb so it does not go LEAN? You do a
> whole lot of pressure testing and engineering - BUT! These were HOME MADE
> FUEL PUMPS - And Manufacturer made Carbs. Transducers were not around
> then. It was too costly to try to figure out how many GPH and How much
> Fuel Pressure would work,and what size spring to use... Too many variables.
> The QUICK and EASY and VERY Effective solution... Put a "T" fitting in
> the line and the excess pressure and excess fuel is returned to the fuel
> tank.
> The Carb takes what it needs - Has a steady supply of fuel and does NOT go
> lean no matter how fast you hit the throttle.
> No Smoke and Mirrors, No ridiculous Vapor Lock theories. But, hell, this
> is aviation so everybody just re-invents the wheel with their own ideas.
>
> I
>
> **
>
>
Message 7
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| Subject: | Re: Fuel return line |
Hello All.
I like the idea that a vapor lock will not occur when the fuel is flowing, this
make scene to me, but will occur on the ground with a hot engine.
The fuel has got to turn to vapor and expand along the fuel pipe so locking it,
and i would not think this would happen in a flowing fuel line.
Engines stop in flight from fuel starvation, but this could be for many reasons,
and if unknown, claimed a vapour lock. But im not convinced,
Kevin, your another high flyer , do you use a oxygen mask up at 17.5
Alan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=398172#398172
Message 8
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| Subject: | Re: Fuel return line |
"Vapour lock" not a good name perhaps occurs when the fuel boils and vapour
flows into the carburetor.=0AThen the mixture is all wrong and the engine
won't give power.=0AIt tends to occur when fuel flow is very low so the fue
l doesn't cool the Rotax pump. Taxying with a hot engine on a hot day=0Athe
n trying to take off.=0ABit of thinking required imho=0AGraham=0A=0A=0A=0A
=0A________________________________=0A From: FLYaDIVE <flyadive@gmail.com>
=0ATo: rotaxengines-list@matronics.com =0ASent: Monday, 8 April 2013, 19:36
=0ASubject: Re: RotaxEngines-List: Re: Fuel return line=0A =0A=0AGraham:=0A
=0AYou have identified yourself as a creator of myths and a woman of Old Wi
fe's-Tales.--Let's take each of your-statements:=0A=0AVapor Lock -
CANNOT be created when there is fuel flow. -As long as the fuel is flowin
g it is not expanding. -It MUST happen at shut down. -UNLESS - as I sai
d some very poor building-practices were followed, which ran a fuel line
next to or above a hot point such as an exhaust pipe. -I'm trying to-be
lieve-that even if the builder made that mistake the DAR would have caugh
t it. -AND isn't this the supposed purpose of installing the "T" fitting.
-=0AVapor Lock requires two things:=0A1 - The fuel to be heated allowing
it to expand and=0A2 - A place for the expanded gas (VAPOR) to be TRAPPED.
=0ASuch a Up or Down U bend or a pig-tail. -=0AEnd of your first myth .
=0A=0ASecond myth: "The fuel return Rotax recommend keeps more fuel flowing
through the system which-helps-cool the pump and ensures cold fuel whe
n you need it for high power." -Where to begin with this one, it is-equ
ivalent-to cleaning the Augean Stables.=0APart A: -If you have two pump
s in series Pump X and Pump Y. -And Pump X comes from the tank and Pump Y
feeds into the carb. -And Pump X feeds at 10 PSI and 10 GPH and Pump Y P
ushes at 12 PSI and 12 GPH what do you think will happen in the connection
between the two pumps? -=0ASince Pump Y requires/displaces more fuel than
Pump X can deliver there will be a LOSS of fuel between the two... -To t
he untrained eye that may look like a Vapor Lock but it is just Fuel Starva
tion. -That is why you place the HIGHER supplying pump (Pump X) before th
e lower-supplying-pump (Pump Y). -You can always reduce what you have
- You can't reduce what you don't have.=0APart B: -If there you have fue
l at Zero Deg F and it is not flowing through the pump there is NO cooling
taking place. -Sure there is some conduction BUT the mass of the fuel pum
p Vs the mass of the fuel in the fuel line and the line itself is NOT worth
considering. -Ah, but I just did, just in case you use-Machiavellian
-Logic. - What kind of fuel lines are people using?=0APart C: -Let's
use some of this-ridiculous-logic that is being-spewed-forth... -
Let's say you have a really-terrible-cooling system on your plane and t
hrough the use of this Magic "T" fitting the Hot fuel is being returned to
the tank. -What about the fuel that is in the line between the electric f
uel pump and the mechanical fuel pump of the HOT engine? Why isn't that cau
sing Vapor Lock? -Then again it may? -All dependent on how well the bui
lder did their job. -=0A=0AQuestions: -How many are using TYGON fuel li
nes? -How many are using-some-other-plastic fuel line?=0A=0AThird myt
h: "Most-carburetor-installations in cars have a fuel-return-line f
or the same reasons." -Most old-carbureted-cars NEVER had a fuel retu
rn line. -As I stated before, when electric fuel pumps came into play the
y needed a method of increasing fuel flow without flooding the carb, theref
ore "T" fittings and fuel return lines. -Fuel return lines came into play
NOT because of Vapor Lock but because of:=0Aa> The EPA - They did not want
gas fumes-evaporating-into the-atmosphere.=0Ab> This was first-fou
ght-by the car manufactures but later was proven to be helpful BECAUSE th
ey were able to brag (advertise) about an INCREASE in gas-mileage... Not
really true - But just that you had more gas in you tank due to less evapor
ation. -How much more? -Ask the EPA!=0AToday all cars have return lines
and pressure gas caps and many have fuel injection. -So if one wants to
use-Machiavellian-Logic here again - - - It was because of Vapor Lock.
-NOT!=0A=0AA Vapor Lock is the Void between a myth being trapped in the m
ind and the truth trying to replace it.=0A=0ABarry=0A=0AHey, I'm 7 days lat
e but: -Did you know you have to do a New W&B if you change from AvGas to
MoGas because MoGas does not have Lead!=0A=0A=0A=0A=0AOn Sun, Apr 7, 2013
at 5:25 PM, GRAHAM SINGLETON <grahamsingleton@btinternet.com> wrote:=0A=0AV
apour lock certainly does occur. I know of several instances, one of which
resulted in a written off aircraft. It happens when the-engine driven fue
l pump-gets heated-by-the engine oil and then heats the fuel. Low fue
l flow rate such as -when-taxiing or waiting for air traffic on the gro
und-can vaporize the fuel, especially Mogas.-The fuel return -Rotax r
ecommend keeps more fuel flowing through the system which-helps-cool th
e pump and ensures cold fuel when you need it for high power.-=0A>Most-
carburetor-installations in cars have a fuel-return-line for the same
reasons.=0A>Graham=0A>=0A>________________________________=0A> From: FLYaD
IVE <flyadive@gmail.com>=0A>To: rotaxengines-list@matronics.com =0A>Sent: S
unday, 7 April 2013, 19:08=0A>Subject: Re: RotaxEngines-List: Re: Fuel retu
rn line=0A> =0A>=0A>=0A>Sacha:=0A>=0A>=0A>You have some great thought provo
king questions. -I hope some are provoked.=0A>Fire sleeves or One piece M
olded Teflon fuel lines are the way to go.=0A>You always want to do all you
can to keep extra heat from fuel and oil lines.=0A>BUT! -Where did this
Old Wives Tail of Vapor Lock come from? -It is a BUNCH OF BUNK!=0A>The "T
" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prev
ent Vapor Lock. -Well, almost nothing - It corrects Pilot/Builder error.
=0A>Vapor Lock happens ON THE GROUND and is-experienced usually at start
up and sometimes in the air,-immediately-during or after rotation.=0A>V
apor Lock can occur with MoGAs or AvGas.=0A>It is more of a POOR PILOT SHUT
DOWN PROCEDURE that anything else.=0A>And since we are talking Home Built P
lanes and-Self Proclaimed-Engineers - - Builder error.=0A>So, what does
the "T" fitting do? -Well, the history goes way back to the 1960's...
-Electric home made Fuel Pumps were being used on-Carbureted-engines.
And the engines were FLOODING like crazy. -Flooding, Fires, Poor-Start
s (if at all), -Dying-when the throttle was floored and Low HP. -All
because of TOO MUCH Fuel Pressure Pushing the-Carburetor's-intake valve
off the seat and flooding the carb.-=0A>So, how do you get more fuel to
the carb so it does not go LEAN? -You do a whole lot of pressure testing
and engineering -- BUT! -These were HOME MADE FUEL PUMPS - And Manufact
urer made Carbs. -Transducers-were not around then. -It was too costl
y to try to figure out how many GPH and How much Fuel Pressure would work,a
nd what size spring to use... -Too many variables.=0A>The QUICK and EASY
and VERY-Effective-solution... -Put a "T" fitting in the line and the
excess pressure and excess fuel is returned to the fuel tank.=0A>The Carb
takes what it needs - Has a steady supply of fuel and does NOT go lean no
-matter-how fast you hit the throttle.=0A>No Smoke and Mirrors, No-ri
diculous Vapor Lock-theories. -But, hell, this is aviation so everybody
==============
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| Subject: | Re: Fuel return line |
Hi Barry,
I think you are only partially right and missed several qualifiers and exacerbating
contributory issues.
They talk about vapor lock in flight, but I have not personally seen it happen,
but there are a thousand different planes designs out there and Rotax didn't
just pull this out of a hat. It probably happened somewhere.
Here are some of the problems. It isn't just fuel flow, it must have a sufficient
quantity flowing so the heat doesn't have time to heat the fuel up to vaporize.
Having exposed fuel lines without fire sleeve not only leaves the fire danger
on the table, but allows for more heat to the fuel. The Rotax or a small
size engine may not flow enough fuel and if the engine is encased in a cowl and
has a lack of or poor air flow and the fuel flow gets reduced and the fuel sets
long enough in the fuel line vapor can happen and the fuel will be flowing.
Vapor lock can happen when an engine is running with fuel flow. My Dad's old Packard
used to get vapor lock especially going up into the mountains at a slow
pace and getting hotter than normal or an engine with a reduced cooling air flow.
It isn't just whether fuel is flowing it depends on the quantity that flows.
If the quantity is very small, but still flowing and in an excessively hot
area it can absolutely vapor lock, just like the old cars. Fuel flow quantity
is the key and the enclosed environment plus heat becomes the next problem. I
usually don't see vapor lock while flying and most never will, but I absolutely
see it all the time after a plane has landed and sat for 30+ minutes. Then on
start up the fuel pressure is 1-1.5 psi until the cooler fuel flows into the
upper fuel lines. In a tightly cowed engine the heat is higher with no fuel flow
right after shut down. That said I haven't seen an engine cough because of
it yet. Putting just a Tee in is really not a re-circulation line. It must have
a restrictor in place otherwise you wouldn't have any fuel pressure. Vapor
lock seems to happen more on the ground and things aren't cooling as well and
there is less fuel flow. A "U" shape fitting won't guarantee or eliminate vapor
lock. As the fuel sits in the hot environment more vapor can form and as it
expands it will over come the "U" fitting area and expand into the hoses. It all
depends on the heat amount, the fuel line surface area, insulating factors(
i.e. fire sleeve), air flow for cooling and fuel flow quantity.
After sitting on the ground and starting up with vapor in the lines, then usually
a taxi out to a runway will take care of the issue.
--------
Roger Lee
Tucson, Az.
Light Sport Repairman - Maintenance Rated
Rotax Repair Center - Heavy Maint. Rated
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
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