Today's Message Index:
----------------------
1. 12:05 AM - Re: Re: Pressure Carburetor? (nico css)
2. 07:18 AM - Re: Pressure Carburetor? (Chris Wall)
3. 07:41 AM - Re: Pressure Carburetor? (N395V)
4. 07:50 AM - Re: Pressure Carburetor? (N395V)
5. 07:55 AM - Re: Re: Pressure Carburetor? (MASON CHEVAILLIER)
6. 08:37 AM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
7. 05:06 PM - Re: Re: Pressure Carburetor? (Bill Bow)
8. 05:06 PM - Re: Re: Pressure Carburetor? (Bill Bow)
9. 06:26 PM - Re: Re: Pressure Carburetor? (WINGFLYER1@aol.com)
10. 06:30 PM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
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Subject: | Re: Pressure Carburetor? |
And when things become challenged, we remain polite. What a great crowd!
-----Original Message-----
From: owner-commander-list-server@matronics.com
[mailto:owner-commander-list-server@matronics.com] On Behalf Of Tylor Hall
Sent: Saturday, September 29, 2007 9:46 PM
Subject: Re: Commander-List: Re: Pressure Carburetor?
JB, Milt and Old Bob,
I what to thank you all for a very interesting discussion about
pressure carbs that are unique to Twin Commanders
I only have a few hours in a 680 and most was in a 500B.
I am looking a owning a 680 at some time and this is the kind of
information that we all need to have.
I do have a questions. Matthew's problem, how do you know the auto
lean is working?
How do you check it? It sounds like the rebuilt side is working and
the older one may not?
The owner of the 680 I am looking at said to leave the mixtures full
forward and pull the throttle back to 2500/ 27in for economy cruse
and it likes to fly at 16,000-18,000 doing 180 kts?
I am glad to see we are all friends on this list.
Tylor Hall
On Sep 29, 2007, at 9:29 PM, N395V wrote:
> <airboss@excaliburaviation.com>
>
> Is Commander ownership a prerequisite to participation in this forum?
>
> I am sure that Sir Barry, Nico, and the good Wing Commander would
> be distressed to hear this. Even though they do not currently own
> Commanders I certainly look forward to their posts and the
> information contained therein. Does their lack of Commander
> ownership diminish thei contributions or knowledge?
>
> I thought it was here that people interested in Twin Commanders
> could discuss these birds and offer opinion.
>
> While I am not a Commander expert having owned 2 different models
> and flown them for several hundred hours along with 37 years and
> many thousands of hours in the air hrs plus has left me with some
> experience and knowledge other Commander owners and operators might
> find helpful.
>
> Old Bob likewise has a lot of time in Beechcraft with the same
> engines as the Commanders. Reading his posts on other forums
> suggests he has a lot of helpful information to impart to Commander
> owners.
>
> In any event you are correct you are not going to change my mind
> and I will fly a Commander or any other plane the way I see fit.
>
> --------
> Milt
> 2003 F1 Rocket
> 2006 Radial Rocket
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=137220#137220
>
>
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Subject: | Re: Pressure Carburetor? |
I am really bummed that I missed the flyin this year, especially
considering that it was held in the best country in the world, Texas.
I look forward to catching up with everyone at the flyin next year.
I couldn't help but jump in on the Pressure Carb debate. In
Dreamcatcher (560E with GO-480-G1B6) we had 6 cylinder EGT on both
engine and digital Fuel Flow, with Pressure Carbs you have to measure
the flow going to the carb and subtract the flow of fuel that is
returned to the fuel tank from the carb to get a correct reading.
During our flight around the world we leaned the engine using the
mixture controls on every flight and operated LOP. The fuel flow and
the EGTs both confirmed the effects that the mixture controls were
having. At full throttle at 12,000 ft with the props pulled back we
had the fuel flow down to 9 GPH per side which we found gave us the
longest range. With the correct instrumentation and only making
changes to one engine at a time at a safe altitude I would encourage
anyone to try it and see the effects for yourself.
Chris Wall
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Subject: | Re: Pressure Carburetor? |
> When I leave the mixture forward The right carb on my 680 leaks about a gallon
or two over night. Since I am a new 680 owner I am trying to learn as much as
I can. Any info would be helpful. Thanks Gil Wingflyer.
>
>
Sorry Gil I missed your earlier post.
You didn't mention where on the carb the fuel leaks from and I really do not know
why it would leak. I would suggest downloading the manual referenced above
and looking down stream from the mixture mechanism. I doubt the leak has anything
to do per se with the mixture control automatic or manual. But if it leaks
on the ground it is probably leaking worse in flight and I would get it corrected
promptly.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137262#137262
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Subject: | Re: Pressure Carburetor? |
> had the fuel flow down to 9 GPH per side
Chris,
Considering the distances you flew I often wondered if you did this. How did you
manage to get all the cylinders to hit peak EGT at the same time?
I had replaced the pressure carb on my M14 with an Airflow performance throttle
body with manual mixture control hoping to run LOP but my 1st cylinder to peak
was at a fuel flow 0.8 GPH more than the last cylinder to peak resulting in
the engine really running rough at peak and LOP.
The M14 pressure carbs appear to be factory set to run about 2-300 degrees F ROP
so even though I can't go LOP it still runs the engine a good bit cleaner and
more efficiently although I had to spend a lot of time tweaking the baffling
to keep CHT's under 380
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137263#137263
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Subject: | Re: Pressure Carburetor? |
cw, you were missed at the flyin. did you ever find any of the mango
air stuff. all of this carb talk makes me glad I have fuel injection.
mason
----- Original Message -----
From: Chris Wall<mailto:cwall@worldflight2000.com>
To: commander-list@matronics.com<mailto:commander-list@matronics.com>
Sent: Sunday, September 30, 2007 9:14 AM
Subject: Commander-List: Re: Pressure Carburetor?
<cwall@worldflight2000.com<mailto:cwall@worldflight2000.com>>
I am really bummed that I missed the flyin this year, especially
considering that it was held in the best country in the world, Texas.
I look forward to catching up with everyone at the flyin next year.
I couldn't help but jump in on the Pressure Carb debate. In
Dreamcatcher (560E with GO-480-G1B6) we had 6 cylinder EGT on both
engine and digital Fuel Flow, with Pressure Carbs you have to measure
the flow going to the carb and subtract the flow of fuel that is
returned to the fuel tank from the carb to get a correct reading.
During our flight around the world we leaned the engine using the
mixture controls on every flight and operated LOP. The fuel flow and
the EGTs both confirmed the effects that the mixture controls were
having. At full throttle at 12,000 ft with the props pulled back we
had the fuel flow down to 9 GPH per side which we found gave us the
longest range. With the correct instrumentation and only making
changes to one engine at a time at a safe altitude I would encourage
anyone to try it and see the effects for yourself.
Chris Wall
http://www.matronics.com/Navigator?Commander-List<http://www.matronics.co
m/Navigator?Commander-List>
Message 6
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Subject: | Re: Pressure Carburetor? |
GREAT TO HEAR FROM YOU!!? Call me at 360-903-6901 on a different topic.? Back to
the carbs.? If all Commanders had a 6 dyl egt and dig fuel flow, maybe it would
be worth messing with.? Yours is the only one I know that is equipped that
way. and?I remember talking to you about the leaning and you said you were running
with the throttles wide open (fuel enrichment valve wide open) so manually
leaning would have made a big difference.? My concern with this thread is that
the poor guy who started this post might try to lean his AMC carbs without
the benefit of that technology.? Like Bob said, this is ancient tech. If your
airplane isn't equipped properly, you can do serious damage to your engines by
messing with the mix and you had better leave it the stink alone.? I am going
to the airport today to get the fuel info from my airplane and check it against
the mfg. fuel flow (I just flew it 16 hours) I'll bet it is within 5%.? GREAT
TO HEAR FROM YOU!!? Lets talk.? jb?
-----Original Message-----
From: Chris Wall <cwall@worldflight2000.com>
Sent: Sun, 30 Sep 2007 7:14 am
Subject: Commander-List: Re: Pressure Carburetor?
I am really bummed that I missed the flyin this year, especially
considering that it was held in the best country in the world, Texas.
I look forward to catching up with everyone at the flyin next year.
I couldn't help but jump in on the Pressure Carb debate. In
Dreamcatcher (560E with GO-480-G1B6) we had 6 cylinder EGT on both
engine and digital Fuel Flow, with Pressure Carbs you have to measure
the flow going to the carb and subtract the flow of fuel that is
returned to the fuel tank from the carb to get a correct reading.
During our flight around the world we leaned the engine using the
mixture controls on every flight and operated LOP. The fuel flow and
the EGTs both confirmed the effects that the mixture controls were
having. At full throttle at 12,000 ft with the props pulled back we
had the fuel flow down to 9 GPH per side which we found gave us the
longest range. With the correct instrumentation and only making
changes to one engine at a time at a safe altitude I would encourage
anyone to try it and see the effects for yourself.
Chris Wall
________________________________________________________________________
Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com
Message 7
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Subject: | Re: Pressure Carburetor? |
This is great!
It hasn't "hit the fan" like this since the "Sump-Gate" days of '01.
bilbo
-----Original Message-----
From: owner-commander-list-server@matronics.com
[mailto:owner-commander-list-server@matronics.com] On Behalf Of N395V
Sent: Saturday, September 29, 2007 8:13 PM
Subject: Commander-List: Re: Pressure Carburetor?
<airboss@excaliburaviation.com>
> HI MILT. I am not picking on you, but need to make one other correction.
Not to worry JB I have a thick skin especially when my espousings are based
on science and data.
This is quite an important topic for any bathtub commander owner and neededs
to be thoroughly discussed.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137190#137190
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Subject: | Re: Pressure Carburetor? |
"Commander ownership is not for everybody"
bb
_____
From: owner-commander-list-server@matronics.com
[mailto:owner-commander-list-server@matronics.com] On Behalf Of
yourtcfg@aol.com
Sent: Saturday, September 29, 2007 10:00 PM
Subject: Re: Commander-List: Re: Pressure Carburetor?
HI MILT
Sorry, but I stand by my statement. Manually leaning a properly adjusted
pressure carb is, wrong. As I had stated in an earlier post (and as said in
the referenced article), it is possible to do it, but why?? Properly
adjusted, the AMC unit does a great job. I just flew my 680E 2800nm, 16hrs
to the fly-in in TX I fueled the outboard tanks and after about an hour on
the main, switched to them They ran 1.5 hours and just as I was reaching
for the selector switch, the LH engine sputtered. I no sooner switched that
engine tha the RH sputtered. The point is, with properly adj carbs, they
are consistent enough to use exactly he same amount of fuel. Not science,
but imperical information. I have flown many bathtub Commanders and have
yet to fly one with an EGT. Short of that installation, leaning the carbs
would be a random gues s at best. Is it possible to squeeze a couple of
extra gallons per hour out of your engines, maybe. But if your Commander
operating budget is so cramped that three or four GPH will make a
difference, I strongly suggest you sell your Commander. BTW, I don't
believe that running over square is bad, (it happens on every TO), or that
you can shock cool and engine with the throttle (rapid mixture change will
however) or that running LOP is bad in a normally aspirated engine. But
manually leaning you AMC carbs is a bad idea, not recomended by the
manufacture of the carb, engine or airframe and completely unnecessary;-)
jb
-----Original Message-----
From: N395V <airboss@excaliburaviation.com>
Sent: Sat, 29 Sep 2007 5:01 pm
Subject: Commander-List: Re: Pressure Carburetor?
<airboss@excaliburaviation.com>
The following is a reprint from "Light Plane Maintenance"
Discussing aircraft mixture control systems. It is lengthy but a good read,
especially the section on pressure carbs and leaning method by type of fuel
distribution system.
As you can see from the article pressure carbs require manual mixture
adjustment
to get the most out of your engine.
JB I think you are a bit premature with the use of the word "wrong"
I do not doubt that you and many Commander pilots and many older pilots were
taught that the mixture control on PS5 pressure carbs is simply an on off
switch. That concept is just plain wrong and needs to be questioned rather
than
just passed on as gospel.
In the old days fuel was a cheap coolant and leaving a pressure carb at full
rich was acceptable practice. It even made its way into some manuals
although I
do not recall seeing it in a commander manual.
Mr Bendix did not attach the mixture control to a "METERING NEEDLE VALVE"
for
the purpose of on and off. If on/off were his intent he would have put a
ball
valve on the carb inlet.
This concept is just as dated as
Don't run oversquare MP>RPM/1000
Rapid throttle reduction causes shock cooling.. Data clearly shows flight
into
precipitation causes greater mor rapid cooling.
Do not run LOP.. Once again date clearly refutes this.
Any way the article follows.
Mixture Control
by LIGHT PLANE MAINTENANCE staff
Part 1 - Mixture Control Systems
Here we go again, another article on mixture management destined to tell
me
things I already know. Well, maybe. It's entirely possible that some
information
will seem repetitious, but, then again, redundancy in aviation isn't such a
bad
thing either. judging from some reader questions, such a revisit to the
topic is
warranted.
Mixture Control is written from the pilot's perspective, by a professional
test-pilot, and is designed to answer the why, when, where and how of
mixture
control and proper leaning procedure for various fuel delivery systems. It
is an
encyclopedia of fuel management. To the layman, it translates into verse as
"How
to avoid burning a hole in your wallet".
Inspite of the proliferation of digital instrumentation, the Basic EGT is
still
an outstanding instrument for monitoring Fuel Flow vs Percent Power. Most of
the
material in this article is based on this basic level of instrumentation and
control. Units of measurement remain in the original Imperial units (oF, for
example) because over 60% of aircraft in use are more than 50 years old.
Air-Fuel Ratios/Distribution
In general terms, mixture is defined as the ratio of air to fuel by weight
(or
more accurately, mass). Most engines will burn air-fuel ratios of 8:1 to 18:
1.
Eight-to-one being very rich and eighteen-to-one being very lean.
The "chemically correct" (otherwise known as stoichiometric) mixture is
about
15:1. This is the mixture ratio where you would expect to find peak EGT in a
perfect burn, but atomization inefficiencies put the peak EGT ratio probably
closer to 13 or 14 to 1.
You might say, "So what's this gobbledygook about ratios? I don't have a
direct
air-fuel ratio indicator in my plane." That's true, but it will help in
understanding the different leaning procedures on different fuel
metering/distributing systems.
The most common fuel distribution systems found in general aviation are:
carburetor, pressure carb, Continental fuel injection, and Bendix fuel
injection. A brief explanation of the operating principles of each system
will
be important in understanding the flight management portion of the pilot's
duties.
Carburetor
The carburetor is a fairly simple device that meters fuel according to the
pressure difference between the downstream side of the fuel jet and the net
pressure of the fuel in the float bowl (affected by net bowl vent and bowl
fuel
head pressure).
This is accomplished using Bernoulli's Principle (venturi in the carb
throat)
and is affected most by the volume of air flow through the carburetor. The
system is, therefore, not very good at compensating for changes in air
density
(weight) caused by any factor, most noticeably, altitude.
The fuel jet (main jet as it's sometimes called) is calibrated to give the
correct rich mixture for the particular engine at full power, sea level, on
a
standard day. A variable valve in series between the float bowl and the
calibrated jet most usually accomplishes mixture control. (Although some
accomplish mixture control functions by varying the bowl vent pressure,
either
way, the result is the same).
Pressure Carburetor
Don't let it fool you. The name implies similarity to the aforementioned
carburetor but the similarity ends there (as anyone who has had to pay for
one
will tell you).
The pressure carburetor is a fairly complex unit that controls fuel/air
ratios
by sensing pressure differences in a venturi and ram air pressure in what's
called a bullet (for what it does to your pocket book if you have to replace
the
bellows inside).
The ram-air pressure is highly dependent on air density (weight) and is
therefore much better at altitude compensation than the carburetor. Mixture
is
controlled by manual adjustment of an internal air control valve that varies
fuel discharge pressure. This is essentially a single-point fuel injection
system [similar to the Throttle-Body Injection (TBI) system used in GM Astro
Vans, etc]
Continental Fuel Injection
in the naturally aspirated engines (except the 10 & G10-550) this system is
purely mechanical. It determines fuel/air ratios solely by reference to pump
RPM, throttle, and mixture valve position. It, therefore, has no way of
sensing
density altitude whatsoever.
Once the pilot sets up the engine for a particular air density (altitude),
minor
throttle and RPM adjustments will not require a mixture adjustment. Properly
adjusted and rigged, this system provides correct rich mixture for the
particular engine at full power and climb at sea level only.
Any operation at altitude requires the pilot to manually control the mixture
to
the optimum setting for the particular MAP and RPM. This is important; any
significant change in air density (generally altitude) requires a
corresponding
mixture adjustment by the pilot.
Turbocharged versions of the Continental Fuel Injection System use an
aneroid to
sense upper deck pressure and adjust fuel pressure, hence fuel now,
accordingly,
and therefore don't require the constant adjustment with air density
changes.
The GIO and I0-550 use a similar aneroid but sense ambient air (hence
altitude)
instead of upper deck pressure.
Bendix Fuel Injection
These systems are very similar, in operation and design, to the pressure
carburetor (including cost, ouch). Enhancements have been made, however,
that
make them more accurate and easier to operate.
This injection system, like the pressure carburetor, is a fairly complex
unit,
which controls fuel-air ratios by sensing pressure differences in a venturi
and
ram air pressure in the bullet.
Most of these systems, however, do not have the AMC (automatic mixture
control)
bellows in the bullet. This makes the unit somewhat sensitive to air density
(weight) changes, providing some altitude compensation. However, manual
mixture
control is still required by the pilot at altitude for optimum performance.
A few of the Bendix Servos do have the AMC bellows in the bullet (some
turbocharged engines) and compensate almost totally for the air density
changes
encountered from sea level to as high as 30,000 feet and sometimes higher.
Operation Block to Block
So how do these differences in systems affect the way you operate the
engine, in
particular the mixture? Let's go over four basic engine operation phases and
how
to operate each system in each phase.
The four operational phases covered will include; taxi & run-up, takeoff &
climb, cruise, and descent & landing. First, though, let's look at the basic
mixture requirements of each phase from an operational standpoint.
Taxi & Run-up
The main consideration on taxi and run-up mixture control is smooth
operation
and the prevention of spark plug fouling. A properly leaned engine can
easily
mean the difference between a good mag check and a bad one. Fouled plugs or
an
overly rich mixture will decrease power and cause bad mag checks. Ground
leaning
will help keep the plugs clean.
Takeoff and Climb
NOTE: All properly adjusted, supercharged and turbocharged engines are to be
at
full rich for takeoff. There are two major concerns in adjusting and
monitoring
the mixture in takeoff (full power operations) and climb mode. Power and
Exhaust
Gas Temperature (EGT) or Turbine Inlet Temperature (TIT).
Best Power mixture comes at about 125oF. Most general aviation engines have
the
capability to carry away the heat generated at Best Power mixtures up to
about
70-75 percent power. Above this power setting, very few, if any, of the
engines
and engine installations we operate can use this mixture setting because of
the
high levels of heat energy being passed through the engine.
This is especially true for takeoff and climb. The higher RPM and manifold
pressures increase the heat passing through the engine in a given time frame
(i.e. more combustion and exhaust scavenge events per second), putting more
heat
into the engine.
There are two ways to decrease this heat and cool things down. Reduce power
(fewer combustion-exhaust scavenge events) or cool the charge in the
combustion
and exhaust events. The idea of takeoff and climb is power, therefore, the
first
option is not so desirable.
By default, the other option becomes the method of choice-cooling the
combustion-exhaust event. This is done nowadays by enriching the mixture.
Some
of the "tried and true" will remember ADI systems (Anti Detonant
Injection-usually a mixture of water and alcohol) in some of the old round
engines and V-12s. ADI does the same thing as enriching the mixture.
At high or emergency power settings, ADI fluid was injected into the intake
air.
Some models of the R-2800 (e.g. F4-U and P-47D) could pull about 80 in. Hg
MAP
with the ADI system engaged and only about 55-60 in. Hg with it off. It got
them
an extra 300 to 400 horsepower when it was needed most.
Contrary to popular belief, actual EGT or TIT temperatures are important to
monitor, especially at takeoff and climb. Many an engine has annealed the
rings
because combustion temperatures got too hot. Rings are annealed (lose their
hardness) by prolonged and elevated temperatures.
As temperatures in an iron alloy (used in piston rings) increase, the time
to
anneal the alloy decreases. Therefore, the less time spent at elevated
temperatures, the better. In practical engine operating terms, keep CHT's
below
400oF and TIT's below 1425oF for this phase.
EGT temps will vary according to probe placement, but a good rule of thumb
in
climb settings is to set the mixture 200oF rich of the peak mixture
temperature
you would get at the 70 percent power setting. This will give good power but
adequate cooling for climb.
Those of you running intercooler systems on your turbocharged engine take
note:
If your fuel system does not fully compensate for changes in air density,
the
fuel system must be set up again after installation of the intercooler.
Fuel systems that do not sense air density from the intercooler will run the
mixture too lean in takeoff end climb (in the neighborhood of 1500oF or
higher)
and will anneal the rings in 50 to 100 hours (oil consumption starts to go
up
and compressions start to drop).
These systems must be set to give a full fuel flow at an equivalent full
power
MAP (generally 3-4 in. Hg below redline). This compensates for the higher
air
density brought by the intercooler. I have brought many a plane back to the
shop
to pull all six cylinders for this very reason.
Cruise
Best Power is used mainly in cruise when you want speed and is shown in
power
charts under the "Best Power" curve. There is also a "Best Economy" curve
that
is a leaner mixture used with the same power setting and gives slightly less
power than the "Best Power" setting (by experience, somewhere around 2-3
percent
lower fuel flow or 3 to 5 knot airspeed loss).
The name is as implied. It gives the best economy for the chosen power
setting
but also gives higher EGTs. "Best Economy" mixture settings generally are
not
given for power settings above 65 percent because of the potential for
preignition and detonation.
Safe EGT levels vary directly with the engine power setting. At low power
settings (65 percent and less) the mixture may be adjusted to give best
economy
because of the engine's ability to carry away the heat energy' at these
lower
settings.
At higher power settings, the mixture is adjusted to allow for extra fuel to
help cool the engine. This is because of the engine's inability to carry
away
the heat energy developed at lean mixtures with high power settings (70
percent
and higher).
This is also the reason most operating handbooks specify seemingly overly
rich
mixtures for climb and high cruise power settings, especially on the larger
engines.
Descent and Landing
Descent is similar to climb in that the mixture must be watched closely in
systems which don't compensate well for changes in air density (carburetors
and
naturally aspirated Continental Fuel Injection systems). The main problem
here
is the reverse of climb: mixture becoming too lean as air density increases
with
a decrease in altitude.
In descents to the pattern altitude from 10,000 to 12,000 feet, if the
mixture
is not increased, opening of the throttle at level-off can be accompanied by
spits and sputters and possibly an engine that quits from fuel starvation.
Good rule of thumb here: set the mixture to maintain the same EGT/TIT as
cruise
minus 50oF to the rich side in high power descents (65 percent or higher)
and
smooth engine running in low power descents (50-60 percent). If you don't
have
an EGT gauge, enrich the mixture to keep the engine smooth plus a little
extra,
as you enter the pattern or level off.
Most normal descents are accomplished at low power (50-60 percent) where
running
close to peak EGT (25oF) isn't a problem because of the lower temps. A
smooth
engine is a happy engine and temps are kept up to help stave off the "shock"
cooling gremlin.
Density compensating systems will do a much better job of mixture control in
descent but still need monitoring and an occasional adjustment. For landing,
the
mixture should be set for a position that will allow for full power
operation
for the particular system. This is to provide sufficient fuel for an
immediate
response if a go-around or evasive maneuver is needed.
Flight and Mixture Control
In [the next section], we'll go through these four flight phases for each
particular fuel system. Keep in mind the time delay (5-10 seconds) for an
EGT or
TIT system reading to stabilize wherever accurate mixture adjustments are
required. Also note that it is important to have your EGT or TIT gauge
calibrated regularly.
Have it checked at each annual if possible, and sooner if you fly more than
150
hours between inspections. This is especially important for turbocharged
engines
and naturally aspirated engines that fly regularly at altitudes below 5,000
feet
MSL.
Or those of you who have Lycoming engines, it wouldn't be a bad idea to get
a
copy of S.I. 1094D, fuel mixture leaning procedure, and look over the
procedures
for your particular engine. You'll find that this Instruction will vary
substantially from the POH or Airplane Flight Manual for larger,
high-horsepower
engines.
2. Mixture Control by Type
[In Part 1] we gave a general mixture operational overview. In parttwo of
this
effort, we will detail the power settings and leaning procedures for each
fuel
system type in various flight modes. Note that this was written by a very
experienced test pilot of GA aircraft, but mixture management is still an
area
of some debate.
Carburetors
Note: The following advice is for naturally aspirated engines only. All
turbocharged and turbo-normalized, carbureted engines must be at full rich
for
takeoff.
Taxi and Runup: Leaning during taxi is sometimes required to prevent plug
fouling and/or to provide smooth operation, especially at highaltitude
airports.
At altitude (3000 feet and higher), leaning is definitely required to get an
accurate mag check.
Rich mixtures can give mag drops of 200 RPM and of only 75 to 100 RPM when
leaned. To find the best mixture for mag checks, lean until the engine gets
rough then enrichen back to highest RPM. Readjust the throttle to the
mag-check
RPM and do your check.
Some carburetor systems provide some challenges to this simple procedure in
cold
weather. The most common example that comes to mind is the 0-470 in the C180
and
C182. This is a great engine/airframe combination but can get cantankerous
in
very cold weather.
The carburetor sits down away from the engine where it can't pick up much
heat.
Therefore, it will ice up a little easier and in very cold weather (low
teens
and subzero) has some problem getting the fuel to atomize once it is
distributed
into the induction airflow.
This can cause lean mixtures of sufficient magnitude to give really rotten
mag
drops; bad enough to fool some into thinking that the mag has just gone
south
with the geese. The best way to compensate for this malady is to pull the
carb
heat on, lean the mixture as previously described, adjust throttle to the
mag
check RPM and try again, all with carb heat "on."
The mag drop will be a little higher than normal (125-150 instead of
75-100),
but will be smooth if everything with the mags is okay. This is to be
expected
because of the hotter induction air (causing lower engine power) with carb
heat
in the "on" position. (Carb heat in for TO.)
Takeoff and Climb: Leaning for takeoff (non-turbo) is a very important
pre-takeoff item at high-altitude airports (higher than 3,000 feet).
Unfortunately this is a practice still not exercised by some. Proper leaning
at
takeoff will shorten takeoff rolls and increase climb rates.
At the high-altitude airports in the Rockies, for example, proper leaning
can
mean the difference between a successful takeoff or ending up in the trees
at
the end of the runway. Proper high-altitude leaning can shorten takeoff
rolls by
500 feet and increase climb rates by 200-300 feet per minute.
Leaning should be accomplished just before the takeoff roll. At full or near
full throttle, lean to peak RPM then enrichen only slightly (barely enough
to
see an RPM drop, no more than 25).
This will be best power for takeoff, plus just a little extra fuel for
cooling
(cooling isn't quite as much of a problem because of the lower temperatures
produced at the lower power found at higher altitudes). The same procedure
should be used for fixed-pitch or constant-speed props. If an EGT is used,
it
should be set for about 150oF rich of peak. At sea level, of course, go full
rich.
Climb is not much different. The idea here is to keep the mixture at best
power
plus about 50oF Mixture adjustment (re-leaning) is required about every
2,000
feet of altitude change for maximum performance and smooth operation above
5,000
feet density altitude.
As altitude increases, and engine power decreases to 65 percent or lower,
the
mixture can be leaned much closer to peak EGT (within 50oF). This will help
maintain power at the lower settings where best power mixture gets closer to
peak EGT.
Cruise: This is the easy part. Set cruise power and lean to 50-75oF rich of
peak
for settings of 65 percent or greater and 25-50oF rich of peak for settings
below 65 percent. This will give you the best mixture setting for longevity
of
your engine and good performance for cruise.
As always, if the engine gets rough before you reach peak EGT, enrichen the
mixture until the engine gets smooth again and then enrichen a little more.
This
is also the procedure to follow if you don't have an EGT gauge. This will
put
you slightly on the rich side of peak EGT.
If your engine is turbocharged (TR182, for example) run 75oF rich of peak
TIT at
65 percent power or greater, and 50oF rich of peak below 65 percent.
Anything
above 75 percent power, should be at least 200oF rich of peak or full rich,
and
no hotter than 1500 F, whichever comes first.
Running at peak EGT anywhere above 55 percent power is not recommended
because
of uneven fuel distribution and this high temperature operating zone has the
smallest margin for mixture errors.
Again, some engines can be very difficult in subzero (Fahrenheit) weather.
You
may have to fly your 0-470 with the carb heat on just to get the mixture to
atomize and the engine to run smooth. This is where a Carb Air Temp gauge
comes
in real handy.
Descent and Landing: Since the carburetor is rotten at air density sensing,
the
mixture will need to be enriched every 2,000 feet or so during the descent.
If
you have an EGT gauge, you can enrichen the EGT 50oF lower than cruise and
maintain this EGT all the way to the pattern.
Once you level Off, enrichen the mixture to the approximate position (by
your
own experience) that you would need if you were taking off at the same
airport.
>From here on out, the mixture can stay where it is until shutdown.
Pressure Carburetors
Taxi and runup isn't much different than normal carbureted engines. Lean for
smooth running to prevent plug fouling and follow the same runup procedures.
At
mag-check RPM, lean the mixture until the engine gets rough or loses RPM,
whichever comes first, then enrichen back to highest RPM. Readjust the
throttle
to the mag-check RPM and do your check.
Takeoff and Climb: For all high-power operations (75 percent power or
greater)
below 5,000 feet density altitude, the mixture control should be full rich.
All
takeoffs (except density altitudes of about 8,000 feet or higher) should
also be
full rich.
The pressure carb is pretty good at sensing actual air density and adjusting
mixture accordingly for fulland high-power. For climbing at higher density
altitudes where power is limited to below 75 percent, the mixture can be
leaned.
For long cylinder/piston/ring life, keep EGTs at 1425oF or lower, preferably
around 1350oF and do not exceed 400oF cylinder head temp.
Cruise: Setup cruise mixture to no less than 50oF rich of peak at power
settings
of 65-70 percent and 75 to 100oF rich at 70-75 percent power. If you don't
have
an EGT, run book settings plus one-half to one gallon per hour more to
extend
cylinder life. In all cases hold CHTs no more than 400oF.
At power settings of 50-65 percent some manufacturers will allow you to run
at
peak EGT. This may be okay for 50-55 percent, but it will prove easier on
your
engine (and pocket book) to run, at minimum, 50oF rich of peak at 60-65
percent.
For supercharged or turbocharged engines add 25oF to the above EGT/TIT
figures
at minimum.
Descent: For descent, subtract 50oF from the cruise EGT-TIT by enriching the
mixture. The AMC bellows should keep the air-fuel ratio pretty stable
throughout
the entire descent.
Some slight adjustment may be required occasionally, but a healthy pressure
carb
will compensate for air density changes, hence altitude, marvelously. Before
applying power at level off, or once in the pattern, enrich the mixture to
the
setting needed for full power at that density altitude.
Some leaning may be required for taxi at high density altitude airports.
Lean as
you would for taxi before takeoff unless extra cooling before shutdown is
required.
Continental Fuel Injection
Taxi and runup will be almost exactly the same as carbureted engines due to
this
system's lack of air density sensing capability. Lean for smooth running
during
taxi and lean the same as the carburetors for runupset mag-check RPM, lean
until
the engine looses RPM, then enrichen back to highest RPM. Readjust the
throttle
to the mag check RPM and do your check.
During this procedure the engine should lose RPM before it gets rough. If it
doesn't this is usually an indication that the system needs a little
attention
(dirty nozzles or injector line obstructions). This is true of injected
engines
in any flight phase.
If it's really noticeable (like a low frequency rumble or panel vibration
that
comes and goes), it would be a good idea to get it checked out before you go
any
further. Obstructions in a line or nozzle can destroy a cylinder in less
than an
hour and may even cause complete piston failure in the takeoff or climb
phase.
Takeoff and Climb: Naturally aspirated engines, as stated in the
description,
have no air density sensing mechanism (exceptions are the 10 and GIO-550,
addressed later). For takeoffs from sea level to 3,000 feet density
altitude,
use full rich mixture. For takeoff at density altitudes of 4,000 feet or
higher,
adhere to the altitude fuel flow settings on the face of the fuel flow
gauge. If
its not marked, consult the POH.
Be sure to use density altitude. Using only pressure altitude will give
inaccurate air-fuel ratios on all but standard temperature days. If for some
reason your flow gauge or POH doesn't give these figures (some old
installations
don't) lean as follows: Just before takeoff, at full or near full throttle,
lean
to peak RPM then enrichen 2-1/2 to 3 gallons per hour (if your gauge is
calibrated only in psi, enrichen two psi).
If you have an EGT, enrich 150oF rich of peak. If your en- gine reaches
red-line
(constant-speed prop) before you get to full throttle, pull the throttle
back to
100 RPM below red-line and follow the above procedure. This will give you
best
power for takeoff and climb for the first one or two thousand feet.
For best climb performance, the mixture will need to be monitored and
adjusted
every 1,000 feet. If you have an EGT gauge, keep the EGT at the same
temperature
it was on take-off. This will give you good perfor- mance and an economical
climb up to about 10,000 feet. At this point re- check peak and adjust for
about
50oF rich of peak for 10,000 feet and higher.
The I0- and GIO-550 series engines have a bellows similar to the aneroid
bellows
on the turbocharged fuel pumps that compensate for changes in air pressure.
If
set up properly, these 550 systems do a pretty good job of mixture control
and
are left at the full-rich position for takeoff and climb until well above
12-13,000 feet.
EGTs on these engines generally run in the low 1400s for takeoff and climb
and,
therefore, don't need leaning even on fairly hot days. The little extra fuel
pumped in this case will be needed to help cool the en- gine anyway.
The turbocharged Continental fuel system is flown like all other turbo-
charged-supercharged systems, with one exception. Set full rich for take-
off,
but for climb, the engine may be leaned to the climb settings on the fuel
flow
gauge face.
For top-end longevity, however, keep climb TITs at or under 1400 degrees F
This
may give you a fuel flow setting of one to one and a half gallons per hour
higher than book but will pay off in the long run.
Cruise: Cruise is not much differ- ent for any naturally aspirated, fuel
injected engine or pressure carburetor equipped engine but it is worth
repeating
here. Set up cruise mixture to no less than 50oF rich of peak at power
settings
of 65-70 percent and 75 to 100oF rich at 70-75 percent power.
If you don't have an EGT, run book settings plus one-half to one gallon per
hour
more to extend cylinder life. In all cases, hold CHTs to no more than 400oF.
At
power settings of 50-65 percent some manufacturers will allow you to run at
peak
EGT. This may be OK for 50-55 percent, but it will prove easier on your
engine
Land pocKet book) to run 50oF rich of peak at 60-65 percent.
For turbocharged engines add 25oF to the above EGT-TIT figures. The 10-550
series is again an exception here. The book allows the engine to be run lean
of
peak at low power settings. The fuel system is designed for the very
accurate
fuel distribution required for this type of operation, but must be
maintained
well to keep the engine healthy.
Remember, with the standard Continental fuel injection system on naturally
aspirated engines, any altitude change will require a corresponding mixture
adjustment. The Continental engine in the early Piper Malibu (TSIO-520-BE)
is an
exception to all of the above. This engine is run either full rich or lean
of
peak, no in between. Run it by the POH.
Descent and Landing: For descent, enrichen the mixture about 50 F and
maintain
the same EGT while descending. Remember, the metering assembly is leaning
the
mixture when you pull back the throttle to maintain the same manifold
pressure,
so you will need a corresponding mixture adjustment to keep the EGT the
same.
Upon pattern entry, the mixture should be enriched to the approximate
position
for a full power setting at that air density (pressure altitude and
temperature), in case full power is needed.
Bendix Fuel Injection
Taxi and Runup: A number of engines with this fuel system like to foul plugs
while taxiing. At the lower RPMs, a fuel valve attached to the throttle
valve
system sets the fuel-air ratio.
The fuel servo does not sense air density or flow until the engine gets to
about
1,700-2,000 RPM. This necessitates manual leaning until approximately 2,000
RPM
at which point the throttle valve rotates fully open and allows the servo to
regulate the fuel-air ratio.
Leaning the mixture to peak RPM during taxi and runup will keep the plugs
clean
and give accurate mag checks at runup.
Takeoff and Climb: This system compensates pretty well for changes in air
density, especially the models with the AMC (Automatic Mixture Control)
(almost
exactly the same as the pressure carb).
Most Bendix systems on naturally aspirated engines, however, have no AMC,
[just
a simple, pitot-like sensor] to sense ram air pressure in the induction.
This
still gives an accurate enough reference for determining air density and
does a
pretty good job of controlling air-fuel ratios. Still, some minor mixture
adjustments must still be made for altitude operations (4,000 feet and
higher).
Just before [entering] the runway, or just before the takeoff roll, run up
to
full or near full power and lean to peak EGT or until the RPM drops
slightly.
Enrichen the mixture 200oF (if you have an EGT) or one and one-half GPH for
four-cylinder engines and two to three GPH for sixcylinder engines. This
setting
will give best power and cooling combination for takeoff and climb.
During climb, the servo will compensate fairly well for air density changes.
A
minor mixture adjustment every 2,000 to 3,000 feet will be needed to keep
the
EGT at the same temperature until cruise altitude is reached.
Again, cruise is not much different for any naturally aspirated, fuel
injected
or pressure carb equipped engine. Set up cruise mixture as described
previously
in this article.
When changing altitudes during cruise with this system, no mixture
adjustments
should need to be made unless the change is more than about 2,000 feet.
Descent and Landing: This is also the same as other injected engines except
mixture adjustments during descent are not as frequent as with the
Continental
system. Enrichen the mixture 50 F just before descent and adjust to keep it
the
same until level off.
Throttle adjustments for descents will need to be made only about every
2,000
feet. If you don't have an EGT installed, enrichen one gallon per hour for
four
cylinder engines or one and one half GPH for six cylinders and maintain the
same
MAP and fuel flow for descent.
Once in the pattern, adjust the mixture to the approximate position for a
full
power setting at that air density (pressure altitude and temperature) in
case
full power is needed. Lean for taxi if at high altitude.
Lean of Peak Operation
Most pilot operational handbooks do not address LOP operation. Lycoming '
particularly, does not like it-although they authorize operating at peak EGT
in
many engines at a limited power level.
Continental is less against it, since they designed the 10-550BE used in the
original Malibus to operate this way, and have comments on LOP operation in
some
of their fuel injected engine handbooks.
Most carbureted engines will not operate very well LOP if at all due to less
than optimum fuel flows to the individual cylinders.
That said, LOP is a viable option for fuel injected engines-even turbos with
the
proper engine monito~ing instrumentation (engine monitors) and proper pilot
technique. When done properly, LOP can extend engine life with cooler
operating
temps compared to running at high power rich of peak. But again, proper
operational training is key.
One source of such training is offered by Advanced Pilot Seminars,
www.advancedpilot.com <http://www.advancedpilot.com/> . Ph 888359-4264 (this
is the phone number for GAMI, in
Ada, Oklahoma who hosts the seminars).
POH Discrepancies
A note about the differences between this article and what you will see in
most
POHs. The fuel flows given in the above advice, as most of you have probably
noticed, are a bit richer (higher) than the POH numbers.
The manufacturers, in an effort to give us better performing aircraft, have
usually used numbers that allow for the most performance and/ or the
greatest
range for a given flight profile (see illustration below). However, these
numbers often do not lend themselves to long engine life.
There is unfortunately a battle between the marketing department and the
engineering department in a given aircraft manufacturer, and the marketing
people usually prevail. Don't believe for a minute that the numbers listed
by
the competition don't significantly influence what ends up in the POH.
Some of the numbers may well be actually obtained by a test pilot in a
perfect
airplane with a perfect engine. Then all the other parameters are
extrapolated
mathematically.
If you look at the engine maker's fuel flow, and other important engine
operational numbers (as opposed to the airplane manufacturer) in their
performance charts you are more likely to see fuel flow numbers
significantly
higher for a given percent of power. Excess fuel in aircraft engines plays a
significant role in cooling the cylinders at high power settings.
There is a high engine longevity price for marginally higher cruise speeds
and
climb rates. Remembering who pays that price will help you get the life you
want
from your engine, if you fly (not fry) with care.
Reprinted courtesy of LIGHT PLANE MAINTENANCE * APRIL/MAY 2004
To subscribe to LIGHT PLANE MAINTENANCE magazine, send an email to
lightplane[at]palmcoastd.com (replace "[at]" with "@" when ready to mail in
order to reduce spam on the airways)
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137185#137185
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Subject: | Re: Pressure Carburetor? |
Milt thanks for the info. It is leaking from the bottom of the carb. I
think it is the carb over flow port. For example, when you prime the carb too
much you see the fuel drip from the carb. The left carb is fine. Thanks Gil
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Subject: | Re: Pressure Carburetor? |
OH NO!! You said the "S" word!!? ;_)? jb
"Sump-Gate"
-----Original Message-----
From: Bill Bow <bowing74@earthlink.net>
Sent: Sun, 30 Sep 2007 5:05 pm
Subject: RE: Commander-List: Re: Pressure Carburetor?
This is great!
It hasn't "hit the fan" like this since the "Sump-Gate" days of '01.
bilbo
-----Original Message-----
From: owner-commander-list-server@matronics.com
[mailto:owner-commander-list-server@matronics.com] On Behalf Of N395V
Sent: Saturday, September 29, 2007 8:13 PM
Subject: Commander-List: Re: Pressure Carburetor?
<airboss@excaliburaviation.com>
> HI MILT. I am not picking on you, but need to make one other correction.
Not to worry JB I have a thick skin especially when my espousings are based
on science and data.
This is quite an important topic for any bathtub commander owner and neededs
to be thoroughly discussed.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137190#137190
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