Today's Message Index:
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1. 08:47 AM - Re: Pressure Carburetor? (yourtcfg@aol.com)
2. 09:03 AM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
3. 09:35 AM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
4. 02:52 PM - Re: Pressure Carburetor? (N395V)
5. 05:01 PM - Re: Pressure Carburetor? (N395V)
6. 05:07 PM - Re: Pressure Carburetor? (N395V)
7. 05:13 PM - Re: Pressure Carburetor? (N395V)
8. 06:18 PM - Re: Re: Pressure Carburetor? (BobsV35B@aol.com)
9. 07:00 PM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
10. 07:28 PM - Re: Pressure Carburetor? (N395V)
11. 07:34 PM - Re: Re: Pressure Carburetor? (BobsV35B@aol.com)
12. 07:53 PM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
13. 08:12 PM - Re: Re: Pressure Carburetor? (COMMANDER560@cs.com)
14. 08:24 PM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
15. 08:30 PM - Re: Pressure Carburetor? (N395V)
16. 08:36 PM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
17. 09:40 PM - Re: Re: Pressure Carburetor? (Tylor Hall)
18. 09:53 PM - Re: Re: Pressure Carburetor? (yourtcfg@aol.com)
19. 11:11 PM - Re: Re: Pressure Carburetor? (BobsV35B@aol.com)
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| Subject: | Re: Pressure Carburetor? |
HI MATT
Yes, fine wire plugs are worth the money, I have them in both?my airplanes.? Also,
All Commanders left the factory with fine wire plugs, even in 1956.? You have
two adjustments on your carbs.? If they are rich on the ground, they are probably
rich in flight.? There is an idle mix adj at the throttle arm (see you
maint manual) and an "off idle" adj.? Both will need to be "tweeked" if the carbs
have been off the airplane.? Call me at 360-903-6901, I talk faster than
i type.? jb
Thinking about going with the wire-type plugs that don't foul.? Good idea??
-----Original Message-----
From: Matthew J. Hawkins <hawkins@cms.udel.edu>
Sent: Thu, 27 Sep 2007 4:33 am
Subject: RE: Commander-List: Pressure Carburetor?
jb-
?
What a?GREAT description of what we've seen!? Thanks so much for passing this on.?
Somehow something so obvious and important has escaped us until now.? Guess
we've had so many things to deal with on this overhaul that this finally rose
to the "top of the pile".
?
Both engines only have about 12-15 hours on them and seem to be running rich -
plugs fouling until getting up to temp.? We could lean the?right side out enough
to get a good mag check, but?left wouldn't lean - though we had less problems
with the left mags than the right.? So this is what?lead us to my question.
?
Thinking about going with the wire-type plugs that don't foul.? Good idea??
?
Sounds like the left side is doing what it's supposed to do.? Right side may still
not be working properly with "auto lean" but sounds like it's not necessarily
a danger - just need to be aware of it for now.? We'll get it looked at -
but at least we understand (now) what the carbs are supposed to be doing.
?
Many thanks to all of you!
?
Matt
-----Original Message-----
From: owner-commander-list-server@matronics.com [mailto:owner-commander-list-server@matronics.com] On Behalf Of yourtcfg@aol.com
Sent: Wednesday, September 26, 2007 10:39 PM
Subject: Re: Commander-List: Pressure Carburetor?
HI MATT.?
It sounds to me like the carb is working properly.? You should never manually lean
your carbs except in case of emergency (like WCG described).? Many years ago
I bought a 560A and as I flew it home I literally read the flight manual, on
my lap,?since I had no idea how to fly the thing.? The manual states that is
is possible to manually?lean the airplane above 10,000 feet.? So, as I crossed
the Rocky Mts, at 12Kt, I decided to lean the engines.? They were running perfect,
but I just could not leave well enough alone.? Well, I learned a couple
of things about Commanders!!? First, you don't need to lean the stinking carbs!!?
Second, whenever you do anything to a twin engine airplane, do it?one engine
at a time.? I reached for the mixture levers and moved them back about 1/2
way.? Nothing happened??? As I continued to pull them back a bit more, BOTH engines
quit cold!!? The silence was defining.? It only took about one millisecond
to get the mixtures back forward.
If you read the lettering on your power quadrant, you will notice that the mixtures
are not labeled "rich" & "lean".? Instead, they say "normal" & "idle cut
off" (Stop & go).
I think you new carb is working great and I wonder why the old carb will allow
you to lean it??? jb
-----Original Message-----
From: Matthew J. Hawkins <hawkins@cms.udel.edu>
Sent: Wed, 26 Sep 2007 9:43 am
Subject: Commander-List: Pressure Carburetor?
All-
Anybody have a good shop they'd recommend that's familiar with working
on/overhauling the older pressure carburetors? We sent the left carb on N2760B
out to one shop - and it came back better in some ways - but mixture is either
full rich or idle cut-off. No adjustment in between.
We've gone through the cabling and linkage and all looks good. We think it's
internal to the carburetor at this point. Not sure, but the shop we used may
have messed something up.
Engines are G0-480-D1A's
Thoughts? Recommendations?
Matt
By the way, on our previous problem (engine skip/roughness when reducing power
through 21" manifold pressure) was exactly as one of you suggested - improperly
adjusted carb heat linkage. Many thanks on that one!
********************
Matthew Hawkins
Director, Marine Ops
R/V HUGH R. SHARP
302-645-4341
FAX: 302-645-4006
hawkins@udel.edu
Email and AIM finally together. You've gotta check out free AOL Mail!
">http://www.matronics.com/Navigator?Commander-List
ics.com
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| Subject: | Re: Pressure Carburetor? |
Sorry Milt, but you are wrong.? Your straight 560?may have?had manually leaning
carbs, the?AUTO lean carbs need to be left in the "normal" position for all flight
and ground operations.? They are NOT to be routinely?adjusted in flight.??That
is why the factory lab;ed the quadrant "normal & Idle cut off" rather than
"rich & lean".? jb???
-----Original Message-----
From: N395V <airboss@excaliburaviation.com>
Sent: Thu, 27 Sep 2007 6:42 am
Subject: Commander-List: Re: Pressure Carburetor?
Let's slow down and think about this for a bit. Unfortunately most of the
original TC drivers mechanics and designers are long gone and we have to rely on
word of mouth OWTs and seat of the pants in flying these things but sometimes
careful analysis of common sense and known physics can be helpful.
It is called a MIXTURE control, not an on/off control. And it is there for a
reason.
This says that as you move the lever it alters the fuel air ratio. It does this
by tightening a diaphragm which lessens the automatic input from the aneroid
barometer and it also slides a precision needle valve in and out of it's seat
adjusting the fuel air mixture/ratio.
The pressure carb also alters the fuel air ratio based on the changing altitude/
ambient pressure as you climb/descend.
While this takes some of the workload off the pilot we all know mixture should
be adjusted relative to peak EGT. Pressure carbs adjusting for altitude only get
a close approximation to getting the mixture to where the engine is happy and
efficient. With AVGAS at $4+ a gallon efficient is becoming very important. Also
the accuracy of the mixture is only as good as the tech that rebuilds or
calibrates the carb. I do not believe there is anyone left alive who can do this
properly on a commander. Last I knew there was only one working test bench left
in existence.
If your carbs were not done on this bench and Jet A or deisel was not used for
calibration then they are NOT working correctly.
Much has been said about "stretching" the diaphragm. This should convince you
that the mixture lever does more than turn things on or off.
The reason to leave it full rich at shutdown is twofold.
1. The diaphragm will dry out and age quickly if you do this,
2. The mixture control also moves a needle valve that is fully seated against a
brass boss in the ICO position. If left in ICO the needle valve will leave an
indent in the brass boss and leak.
The correct way to lean a normally aspirated pressure carb in a Twin Commander
is......
When at altitude (over 5000') and you have full throttle and the props set, pull
the throttle back till you get the 1st visible decrease in manifold pressure.
then advance the throttle to max Manifold pressure obtainable. The manual and
many old timers would now say you are leaned. But you have that nice red lever
that puts tension on a diaphragm and moves a needle valve both of which adjust
fuel air ratio. Now why was it put there?
So in the best of all worlds you have an engine monitor that monitors all your
EGTs and CHTs as well as a fuel flow indicator for each engine.
Then you can lean to peak if under 65% power (which you will be under at
altitude) or if you are a wuss lean somwhere ROP or if a real man try to go LOP
if the engine remains smooth.
If you do not have the fancy gizmos then lean till the engine gets rough then
push it a skosh forward.
In my 560 this invariably saved me 2.5 GPH per engine at cruise or 5 GPH total.
at 300 hrs a year this adds up to mucho deniro.
In the super charged versions your throttle will be set at wherever you set it
for cruise so just lean till rough then enrichen. In the supercharged versions
you need to be cautious and remain ROP as you most likely will be above 65%
power and can cause harm at peak and LOP. To remain ROP do not dally when the
engine gets rough bump that red rascal forward about an eighth of an inch
quickly.
A caveat is the 560Fs for some reason the engine/carb combination on these
setups will often do as JB described that is they go from cruise to silence. I
suspect this has more to do with poor rebuild or calibration and maintenance
than the setup it self.
I have found after several years of playing with LOP operations using engine
analyzers that if your goal is efficiency and safe operation while running ROP
then the lean to rough and a skosh forward on the mixture control will put your
mixture lever in exactly the same place the fancy expensive engine monitor will
have you put it by using their auto lean algorithms.
If you like to play with LOP and have FI and a super or turbocharger do not even
attempt it without an engine analyzer.
If you lean correctly and control temps correctly not only does this save fuel
but more importantly in these old birds it will greatly prolong engine life.
Well that was a long post and I hope helpful.
The short answer to the original post is your carbs (statistically) are most
likely not calibrated correctly and while they may be safe I would not assume
so.
I cannot remember the shop or tech that can do it but the name Czarnecki in
Oklahoma rings a bell as does the word "precision" in the shop name. One of the
old timers should be able to steer you there. It may also be listed somewhere in
the old Commander list archives that I believe Nico is the keeper of.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=136751#136751
________________________________________________________________________
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| Subject: | Re: Pressure Carburetor? |
HI MILT.? I am not picking on you, but need to make one other correction.? This
may be why you were saving gas by manully leaaning you carbs.? On normally asperated
engins, equiped with auto lean carbs, it is important to retard the throttls
in cruse.? These carbs are equiped with a enrichment valve that is opened
at throttle settings above 80%.? This feature uses fuel to cool the engine
durring climb and high power settinsg.? Once you reach you cruse altitude, you
should retard the throttls as far as possible and still maintane the desired
MP.? This closes the enrichment valve and alows the carb to adjust the mix properly.?
If the throttle is left fully forward, the ericment valve will reamin
open, defeating a portion of the auto lean circut.? jb
When at altitude (over 5000') and you have full throttle and the props set,
-----Original Message-----
From: N395V <airboss@excaliburaviation.com>
Sent: Thu, 27 Sep 2007 6:42 am
Subject: Commander-List: Re: Pressure Carburetor?
Let's slow down and think about this for a bit. Unfortunately most of the
original TC drivers mechanics and designers are long gone and we have to rely on
word of mouth OWTs and seat of the pants in flying these things but sometimes
careful analysis of common sense and known physics can be helpful.
It is called a MIXTURE control, not an on/off control. And it is there for a
reason.
This says that as you move the lever it alters the fuel air ratio. It does this
by tightening a diaphragm which lessens the automatic input from the aneroid
barometer and it also slides a precision needle valve in and out of it's seat
adjusting the fuel air mixture/ratio.
The pressure carb also alters the fuel air ratio based on the changing altitude/
ambient pressure as you climb/descend.
While this takes some of the workload off the pilot we all know mixture should
be adjusted relative to peak EGT. Pressure carbs adjusting for altitude only get
a close approximation to getting the mixture to where the engine is happy and
efficient. With AVGAS at $4+ a gallon efficient is becoming very important. Also
the accuracy of the mixture is only as good as the tech that rebuilds or
calibrates the carb. I do not believe there is anyone left alive who can do this
properly on a commander. Last I knew there was only one working test bench left
in existence.
If your carbs were not done on this bench and Jet A or deisel was not used for
calibration then they are NOT working correctly.
Much has been said about "stretching" the diaphragm. This should convince you
that the mixture lever does more than turn things on or off.
The reason to leave it full rich at shutdown is twofold.
1. The diaphragm will dry out and age quickly if you do this,
2. The mixture control also moves a needle valve that is fully seated against a
brass boss in the ICO position. If left in ICO the needle valve will leave an
indent in the brass boss and leak.
The correct way to lean a normally aspirated pressure carb in a Twin Commander
is......
When at altitude (over 5000') and you have full throttle and the props set, pull
the throttle back till you get the 1st visible decrease in manifold pressure.
then advance the throttle to max Manifold pressure obtainable. The manual and
many old timers would now say you are leaned. But you have that nice red lever
that puts tension on a diaphragm and moves a needle valve both of which adjust
fuel air ratio. Now why was it put there?
So in the best of all worlds you have an engine monitor that monitors all your
EGTs and CHTs as well as a fuel flow indicator for each engine.
Then you can lean to peak if under 65% power (which you will be under at
altitude) or if you are a wuss lean somwhere ROP or if a real man try to go LOP
if the engine remains smooth.
If you do not have the fancy gizmos then lean till the engine gets rough then
push it a skosh forward.
In my 560 this invariably saved me 2.5 GPH per engine at cruise or 5 GPH total.
at 300 hrs a year this adds up to mucho deniro.
In the super charged versions your throttle will be set at wherever you set it
for cruise so just lean till rough then enrichen. In the supercharged versions
you need to be cautious and remain ROP as you most likely will be above 65%
power and can cause harm at peak and LOP. To remain ROP do not dally when the
engine gets rough bump that red rascal forward about an eighth of an inch
quickly.
A caveat is the 560Fs for some reason the engine/carb combination on these
setups will often do as JB described that is they go from cruise to silence. I
suspect this has more to do with poor rebuild or calibration and maintenance
than the setup it self.
I have found after several years of playing with LOP operations using engine
analyzers that if your goal is efficiency and safe operation while running ROP
then the lean to rough and a skosh forward on the mixture control will put your
mixture lever in exactly the same place the fancy expensive engine monitor will
have you put it by using their auto lean algorithms.
If you like to play with LOP and have FI and a super or turbocharger do not even
attempt it without an engine analyzer.
If you lean correctly and control temps correctly not only does this save fuel
but more importantly in these old birds it will greatly prolong engine life.
Well that was a long post and I hope helpful.
The short answer to the original post is your carbs (statistically) are most
likely not calibrated correctly and while they may be safe I would not assume
so.
I cannot remember the shop or tech that can do it but the name Czarnecki in
Oklahoma rings a bell as does the word "precision" in the shop name. One of the
old timers should be able to steer you there. It may also be listed somewhere in
the old Commander list archives that I believe Nico is the keeper of.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=136751#136751
________________________________________________________________________
Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com
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| Subject: | Re: Pressure Carburetor? |
I was wondering if anyone was paying attention.
Nope the 560 had pressure carbs. It is odd that you have a lever that moves 4-5
inches and moves things inside the carb for just on and off. Seems it would have
been simpler to just out an on/off valve at the carb inlet.
I had a Cessna that had a mixture controlo labelled only open and idle cutoff.
It was certainly there to control mixture.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137167#137167
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| Subject: | Re: Pressure Carburetor? |
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. 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? |
Back to the original post is an excerpt from the old commander archives and Republic
CB Archives by Chris Schuerman with a blurb on the PS%. Chris too believes
the mixture control should not be touched. When I asked him why he said "someone
told me".
At the end of Chris's post are contacts for calibration of your pressure carb.
The excerpt is in pdf format as an attachment
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137187#137187
Attachments:
http://forums.matronics.com//files/ps_5bdpercent20opspercent20big_148.pdf
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| Subject: | Re: Pressure Carburetor? |
> 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? |
Good Evening Milt,
I am beginning to wonder if the Commander list has decided that I do not
belong here. I mentioned a lot of what has been discussed here a few days ago,
but there has not been a single comment made either disagreeing with what I
said or agreeing with my position.
Nevertheless, my thick skin allows me to try again!
The PS5c has always needed to be manually leaned and it is definitely a
"Pressure Carburetor."
There was mention in the attachment of the Advanced Pilot's Seminar at Ada,
Oklahoma.
I also would agree that attendance at that program is well worthwhile, but I
am amazed that the author recommends running any engine fifty rich of peak
after attending that course. Fifty rich of peak is OK for those cases were it
is needed to get adequate power to operate the airplane, but at any other
time, fifty rich of peak EGT is about the hottest place the engine can be
operated. It is a bit below best power which is why it is recommended so often
by
the sales department of any manufacturer, but it is certainly NOT a place that
would automatically be easy on the engine.
I think the author will agree that running cool is a good idea. The engine
can be run coolest by running well lean of peak. Whether or not that most
desirable of operations can be conducted is dependent on the quality of the fuel
distribution between the various cylinders. Thus the need for balanced
injectors!
Lindbergh was messing with that with his three throat carburetor before
leaving for Paris. This is not new stuff and it is not rocket science.
During the last fifty years, there have been many attempts to dumb up the
operation of our engines.
That is why you see the various setups that tell the pilot to run the engine
at full rich and to only touch the mixture when he/she wants to shut it
down. While all those efforts have been admirable, we still do not have any fuel
control unit that works that well.
If someone does not feel they can spend the time attending the two and half
day class at Ada, they should try the home study course. If they don't want to
pay the price to take the home study course, they should at least read the
free stuff written and freely presented by one of the instructors, John
Deakin. He has written a complete set of articles about everything that has been
discussed in this thread and presented it free to all as a series of articles
on AvWeb. Contact him at: _jdeakin@advancedpilot.com and_
(mailto:jdeakin@advancedpilot.com%20and) he will happily tell you where to download all of his
articles free of charge!
The knowledge is there. It just needs to be studied by anyone planning to
operate any high powered piston engine.
Incidentally, I'll bet you will find Chris S. will agree with my assessment!
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503
In a message dated 9/29/2007 7:08:44 P.M. Central Daylight Time,
airboss@excaliburaviation.com writes:
At the end of Chris's post are contacts for calibration of your pressure
carb.
The excerpt is in pdf format as an attachment
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| Subject: | 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 guess 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?
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. 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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Message 10
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| Subject: | Re: Pressure Carburetor? |
Glad you mde it home OK JB, Wish I could have been there,
> it is possible to do it, but why??
If you go to this link
http://www.navioneer.org/riprelay/The%20Navion%20Files/Bendix_Carb.pdf
(Link courtesy of Craig C.
you will find an entire installation and operation manual for the PS series pressure
carbs. It is a 12 MB download.
The why is because Mr Bendix says to as evidenced in the page copied from the manual
and attached below. The entire download has description of operation as
well as drawings of the carb and its internal components.
You have frequently mentioned to many of us about cramped budget sell your commander
and "Commander ownership isn't for everybody" That is not a good reason
to continue to operate a plane incorrectly.
Its not a matter of cramped budget. Its a matter of dispelling bad practices that
have been passed on by word of mouth for generations in the face of overwhelming
evidence that refutes them.
It is a matter of changing your ways when they are replaced by something better.
I fly 300 hrs a year that would save me 1200 gallons of fuel or at todays price
$4800. Thats a years tuition for my Sons college, A downpayment on a new car.
A trip to Hawaii. Or it would fund one heckuva Twin Commander flyin.
Those good enough reasons. How about running an engine correctly will make it last
longer. Not an insignificant thing considering how hard parts are to come
by for these old engines.
> not recomended by the manufacture of the carb
But it is as you can see in the attachment below.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137210#137210
Attachments:
http://forums.matronics.com//files/bendix_ps_series_162.jpg
Message 11
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| Subject: | Re: Pressure Carburetor? |
Good Evening JB,
Why?
Because it is easier on the engine and increases the payload.
I think it is wrong to ever operate any engine richer than it needs to be
operated.
That is not only wasting a precious resource, but it shortens the range or
reduces the allowable payload of our flying machines.
The pressure carburetors we had on our big round engined airliners were as
sophisticated as any that have ever been used on any GA aircraft, but we still
leaned them manually when we had the time and the knowledge to do it
correctly. We all hope for the day when FADEC will allow us to operate our airplanes
the way we operate our automobiles, but none of the AMC equipped airplanes
have ever reached the point where they were as efficient as the manually
operated version IF it was operated properly by a knowledgeable operator.
An engine that has good fuel balance and that is being operated on the lean
side of peak EGT will run cooler and cleaner than that same engine when it is
developing that same power only being run rich of peak. I think you and
everyone else will agree that cooler and cleaner is better!
It does take knowledge and training, but isn't training and knowledge
required for most of our aviation endeavors?
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503
In a message dated 9/29/2007 9:01:40 P.M. Central Daylight Time,
yourtcfg@aol.com writes:
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??
Message 12
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| Subject: | Re: Pressure Carburetor? |
? Obviously I am not going to change any minds.? Tell you what,?fly your Commander?any
way you want, or do any of you guys even?have a Commander??? jb?
-----Original Message-----
From: BobsV35B@aol.com
Sent: Sat, 29 Sep 2007 7:32 pm
Subject: Re: Commander-List: Re: Pressure Carburetor?
Good Evening JB,
?
Why?
?
Because it is easier on the engine and increases the payload.
?
I think it is wrong to ever operate any engine richer than it needs to be operated.
?
That is not only wasting a precious resource, but it shortens the range or reduces
the allowable payload of our flying machines.
?
The pressure carburetors we had on our big round engined airliners were as sophisticated
as any that have ever been used on any GA aircraft, but we still leaned
them manually when we had the time and the knowledge to do it correctly. We
all hope for the day when FADEC will allow us to operate our airplanes the way
we operate our automobiles, but none of the AMC equipped airplanes have ever
reached the point where they were as efficient as the manually operated version
IF it was operated properly by a knowledgeable operator.
?
An engine that has good fuel balance and that is being operated on the lean side
of peak EGT will run cooler and cleaner than that same engine when it is developing
that same power only being run rich of peak. I think you and everyone
else will agree that cooler and cleaner is better!
?
It does take knowledge and training, but isn't training and knowledge required
for most of our aviation endeavors?
?
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503
?
In a message dated 9/29/2007 9:01:40 P.M. Central Daylight Time, yourtcfg@aol.com
writes:
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???
See what's new="_blank">Make AOL Your Homepage.
________________________________________________________________________
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Message 13
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| Subject: | Re: Pressure Carburetor? |
Hi everyone, I flew a 680E for a company in the 60's , and before that a
straight old 560, and was checked out by a pilot from a commander dealership, I
believe it was Southern Ohiio Aviation, he instructed me as JB said to leave
those mixtures forward, always, worked good, lasted a long time, also proven by
Audie Melton, who flew Bull Hancocks, of Lexington, Ky, (Clairbourne Farms,
race horses )720 thur 4 sets of engines. Just my old two cents worth, Thanks,
Joe Shepherd
Message 14
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| Subject: | Re: Pressure Carburetor? |
HI MILT Had a great trip home and the fly-in was great too!!? Maybe we are having
a miscommunication.? The PS5C carburetor is a pressure carb, and?does use a
Mixture control.? It is not an auto lean carb.? A PS5C(D) does have an AMC unit
and "Mr. Bendix" does not recommend messing about with that one.? Page 16,
par 2.6 of the Bendix PS manual reads?? "A manual mixture control valve is provided
as a means of correcting for natural enrichment at altitude?on carburetors
without automatic mixture control"? jb?
-----Original Message-----
From: N395V <airboss@excaliburaviation.com>
Sent: Sat, 29 Sep 2007 7:27 pm
Subject: Commander-List: Re: Pressure Carburetor?
Glad you mde it home OK JB, Wish I could have been there,
> it is possible to do it, but why??
If you go to this link
http://www.navioneer.org/riprelay/The%20Navion%20Files/Bendix_Carb.pdf
(Link courtesy of Craig C.
you will find an entire installation and operation manual for the PS series
pressure carbs. It is a 12 MB download.
The why is because Mr Bendix says to as evidenced in the page copied from the
manual and attached below. The entire download has description of operation as
well as drawings of the carb and its internal components.
You have frequently mentioned to many of us about cramped budget sell your
commander and "Commander ownership isn't for everybody" That is not a good
reason to continue to operate a plane incorrectly.
Its not a matter of cramped budget. Its a matter of dispelling bad practices
that have been passed on by word of mouth for generations in the face of
overwhelming evidence that refutes them.
It is a matter of changing your ways when they are replaced by something better.
I fly 300 hrs a year that would save me 1200 gallons of fuel or at todays price
$4800. Thats a years tuition for my Sons college, A downpayment on a new car. A
trip to Hawaii. Or it would fund one heckuva Twin Commander flyin.
Those good enough reasons. How about running an engine correctly will make it
last longer. Not an insignificant thing considering how hard parts are to come
by for these old engines.
> not recomended by the manufacture of the carb
But it is as you can see in the attachment below.
--------
Milt
2003 F1 Rocket
2006 Radial Rocket
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=137210#137210
Attachments:
http://forums.matronics.com//files/bendix_ps_series_162.jpg
________________________________________________________________________
Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com
Message 15
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| Subject: | Re: Pressure Carburetor? |
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
Message 16
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| Subject: | Re: Pressure Carburetor? |
SORRY MILT, I did not mean to offend.??As you said, it is an important subject
and I needed to set it straight.? Sorry.? jb
I thought it was here that people interested in Twin Commanders could discuss
these birds and offer opinion.
-----Original Message-----
From: N395V <airboss@excaliburaviation.com>
Sent: Sat, 29 Sep 2007 8:29 pm
Subject: Commander-List: Re: Pressure Carburetor?
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
________________________________________________________________________
Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com
Message 17
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| Subject: | 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
>
>
Message 18
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| Subject: | Re: Pressure Carburetor? |
HI TYLOR
You can generally tell if the autolean is operating by engine performance.? If
the carb fails, it is designed to fail safe and run super rich.? You can then
manually lean it until it can be repaired.? On the Commander, look for the cyl
temps to run the same on both engines, at climb and cruse.? To check normal operation,
set cruse power and slowly lean the carbs manually (one at a time thank
you)? The levers should travel about 1/2 way with little or?no change in engine
operation.? When the change comes, it should be very quick.? It should go
from running fine to idle cut-off in a very little travel.? Last, check the
color of the exhaust pipes.? They should be a nice ash gray.? jb
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??
-----Original Message-----
From: Tylor Hall <tylor.hall@sbcglobal.net>
Sent: Sat, 29 Sep 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:?
?
>?
> 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?
>?
>?
>?
>?
>?
>?
>?
>?
>?
>?
?
?
?
________________________________________________________________________
Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com
Message 19
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| Subject: | Re: Pressure Carburetor? |
Good Morning Tylor,
The way I look at it is like this. Forty years ago, the best we knew how to
do was build a very sophisticated fuel controller which could do a reasonable
job of running our engine with minimal assistance from the pilot.
Even in those days, when adequate instrumentation and inflight personnel
were available to operate the engine more efficiently, manual leaning was done.
The desire has always been to run the engine as safely and efficiently as
possible given what was available.
The three chamber pressure injection carburetor equipped with an Automatic
Mixture Control was the FADEC of it's day.
Since it was the state of the art, there were a number of shops and many
personnel that knew how to maintain it and keep it in good adjustment. Have you
tried to buy new parts for some of that ancient technology equipment?
We no longer have the luxury of having readily available maintenance of that
ancient technology, but we do have much better and more modern engine
instrumentation which will allow us to manually accomplish what the AMC units
were
designed to do. In fact, with that modern instrumentation, we can do a much
better job than any of the automatic equipment was able to do fifty years ago.
We can use all that fancy electronic stuff as a full time flight engineer who
never lets his eyes wander from the engine being monitored.
The low frequency radio range worked well during those same times when we
were using the AMC units. How many of us are still using low frequency radio
ranges as navigation equipment?
The years have given us new tools to work with. The goal has not changed,
but our ability to operate the engines the way the designer wanted them to be
operated has changed a lot.
Personally, I think I have learned a lot in the sixty-one years since I
soloed and I hope to continue to learn and adapt to new technology for what years
I do have left to pilot airplanes.
I like engine monitors and I like GPS.
Low frequency ranges were challenging and satisfying to use, but GPS is
better.
The same analogy works for using ancient fuel controllers or using modern
engine control techniques. The goal is the same. Simple, safe and efficient
operations. Modern equipment allows us to do the job better all the time.
As I said before, it does take an open mind and a bit of education, but
isn't the challenge of aviation one of the reasons we all enjoy it so much?
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503
In a message dated 9/29/2007 11:41:09 P.M. Central Daylight Time,
tylor.hall@sbcglobal.net writes:
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?
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