To Lean or not to lean
 

Have just had an interesting conversation at the club

I said that a business running an air transport business where the engine can only go to TBO and or 12 years from zero time / new engine will run the engine in the cruise leaned as far as is sensible, this is of course to save money by minimising fuel costs.

I said he can do this as he is forced to have an overhaul long before the engine is clapped out (here read running "on condition") and so is unlikely to finding himself having to change cylinders with burnt exhaust valves and other problems.

However when an engine is run by a group "on condition" if you run without leaning at any time you are likely to get longer cylinder life.

What do people think about that and indeed are there any reference works which give some science on this.

Both Lycoming & Continental publish guidelines for the correct techniques for leaning engines and the fuel savings are in the order of 20%.

Use the manufacturers data rather than what some bloke on the internet said and you won’t go wrong .

Don't know where you picked up that old wives tale, grief can be caused if you don't break in a new engine properly, it glazes the cylinders and results in high oil consumption, here is what Lycoming have to say in their "Flyer"publication re leaning.

The information outlined in this presentation has been reduced to minimum essential facts, and is based on leaningas described in the various Avco Lycoming “Engine Operator"s Manuals”, and our Service Instruction No. 1094, “Fuel Mixture Leaning Procedures”.

Although the above documents are authentic basic references on leaning, and including the related write-ups in past issues of the “Flyer”, we see the need to review all of these and outline the basic combined information in one article for the following reasons:

l. The basic leaning information needs to be repeated from time to time.

2. We need to update our information on new engine models, or concerning new and improved engine instrumentation.

3. Operators in the field have stated that some of the Pilot‘s Operating Handbooks lack sufficient information on leaning.

4. The engine manufacturer with the approval of the FAA and in cooperation with the airframe manufacturer, is the authority on the operation of his product.

5. Small aircraft, such as the typical Genera] Aviation trainer, have limited engine instrumentation. Therefore, we provide the operator with certain basic leaning niles to protect the powerplant and yet operate it efficiently. Damage to this type of engine results from leaning at higher than the manufacturer’s recommended cruise power.

6. The more‘ complex powerplants of higher horsepower or higher compression ratios (200 HP and higher), are generally accompanied by sufficient engine instrumentation to protect the powerplants while operating at approved higher than routine power settings. However, the engine manufacturer helps protect these engines by establishing certain requirements for leaning at higher than average cmise power by reference to fuel flow, exhaust gas temperature, or turbine inlet temperature, cylinder head temperature, oil temperatures and pressures. The airplane pilot’s manual will specify this information for these more complex high performance powerplants.

WHY LEAN THE ENGINES?

In spite of a number of variations in the different models of our powerplants, there are some general recommendations on leaning we can offer for all Avco Lycoming engines.

l. Most carburetors or fuel injectors are set slightly on therich side-—this calls for leaning at any altitude at the manufacturer‘s recommended cruise power.

2. Proper leaning means economy of fuel, which results in lower cost of operation.

3. Rich running engines cause roughness -— proper leaning makes them smooth, which protects engine mounts and engine accessories from undesirable vibration and possible failure.

4. An engine properly leaned is a more efficient powerplant.

5. Leaning at cruise can extend the range of the aircraft - a safety factor.

6. Proper leaning means less spark plug fouling and longer life for plugs — also a safety factor, as well as lower maintenance cost.

7. Correct leaning means cleaner combustion charnbers and less likelihood of pre-ignition from undesirable combustion deposits.

8. Proper leaning at cruise power results in more normal engine temperatures in cool weather or at the cooler temperatures of altitude. Rich mixtures cause undesirable cool engine temperatures in cool or cold weather.

a. Oil temperatures should be at least 165° F minimum in order to reduce moisture forming vapors and undesirable acids in the engine oil.

The Three Basic Types of Fuel Metering Devices Used with Avco Lycoming Engines In General Aviation; and the General Procedures for Leaning at Manufacturers’ Recommended Cruise Power:

1. Float type carburetor.

a. Fixed pitch propeller -— lean to a maximum increase in RPM and airspeed — or — just before engine roughness.

(1) Engine roughness is not detonation at cruise power, but is caused by the leanest cylinder not firing due to a very lean fuel-air mixture which will not support combustion in that cylinder.

b. Controllable propeller — lean the mixture until roughness encountered, and then enrich slightly until roughness is eliminated and engine is smooth. There may be a slight increase of airspeed noted in smooth air when properly leaned at cruise when compared to full rich.

c. The EGT offers little improvement in leaning the float-type carburetor over the procedures outlined above because of the problem of imperfect distribution. However, if the EGT is installed, a good rule of thumb is lean the mixture plus 50° on the rich side of peak EGT with this type of fuel metering device.

d. With the application of carburetor heat, the mixture is richer; check and adjust mixture leaner.

2. Pressure Carburetor. All Lycoming powerplants using the pressure carburetor have an automatic mixture control which eliminates manual leaning as a routine.

a. No manual leaning unless the aircraft has reliable fuel flow equipment.

b. Cylinder head temperature gage should be a required instrument.

c. EGT of little practical value with the automatic mixture control unless manually leaned by cross reference to reliable fuel flow equipment.

3. Fuel Injection.

a. Because of the varied models of fuel injectors used with Avco Lycoming engines, the operator must consult the specific Pilot’s Operating Handbook for specific leaning instructions.

b. However, as a basic technique, at the manufacturer’s recommended cruise power limitation, with a m. .al mixture control, lean initially by reference to the fuel flow (if available) for the percent of cruise power without exceeding manufacterer’s recommended limits. Then for more precise leaning, if an exhaust gas temperature is available, find peak EGT without exceeding limits, and operate there, or by the rule of thumb of plus 50 F on the rich side of peak EGT.

(1). Monitor cvlinder head temperatures.

(2). The EGT is a helpful instrument for precise leaning with fuel injection.

(3). If EGT and fuel flow are not available, then leanto just outside roughness, or to a slight airspeed loss then as desired by the pilot.

LEANING RECOMMENDATIONS FOR TYPES OF AVCO LYCOMING ENGINES

1. Direct drive normally aspirated engines, (carbureted or fuel injection);

a. May be leaned at any altitude, at manufacturer’s recomcommended cruise power (usually 75% or less), provided there is a manual mixture control.

b. In climb from sea level through 5,000 ft. density altitude, mixture must be full rich. Continued climb above 5.000 ft., mixture may be leaned for smooth engine operation. DO NOT confuse the 5,000 ft. for climb with the cruise configuration.

c. Operations at higher than 75% power without reference to fuel flow, cylinder head temperatures, and without knowledge of specific power, requires full rich mixture.

(1). Leaning at recommended cruise power does not damage a normally healthy engine, but leaning at higher than 75% cruise power in this type ofengine can cause engine damage when complete engine instrumentation is not available (CI-IT and fuel flow minimum), and limitations not spelled out in airplane pilot’s operating handbook.

2. Leaning the turbocharged Lycoming powerplant.

a. The turbine inlet temperature gage (TIT) is a required instrument with turbocharging by Lycoming.

b. During manual leaning, the TIT must not exceed 1650°F (900C). (The TO-360 is an exception).

c. At cruise power when leaning the mixture, if TIT reached 165O° F before peaking, then do not exceed 165O° to find peak.

d. Operations may be at peak during cruise provided TIT does not exceed red line maximum and cylinder head should not exceed 435° F (224° C), for continuous operation.Mixture may be operated anywhere on the rich side of peak. CHT, fuel flow, and TIT will decide where lhe pilot will operate his mixture control as specified in the Pilot’s Operating Handbook.

e. Very high altitudes may result in high temperatures which will require adequate fuel, cowl flaps, or airspeed tor cooling.

f. All takeoffs with turbocharged powerplants (where turbo is operating) must be at full rich mixture regardless of airport elevation. The turbocharged engine needs the extra fuel for cooling because of the high induction air temperatures created by turbocharging, and because the engine is operating at sea level horsepower.

g. Always consult the Pilot’s Operating Handbook for any variations for the specific aircraft. If leaning by means of manual mixture is permitted at climb power, it will be specified in the Pilot’s Operating Handbook and will list required ranges for fuel flow, power settings, and temperature limitations.

Leaning the supercharged Lycoming powerplants.

a. All takeoffs with supercharged powerplants must be at full rich mixture regardless of the airport elevation. The supercharged engine needs the extra fuel for cooling because of the high induction air temperatures created by supercharging, and because it is operating at sea level horsepower.

b. If leaning by means of manual mixture is permitted at climb power, it will be specified in the Pilot’s Operating Handbook, and will list required ranges for fuel flow, power settings, and temperature limitations.

c. The exhaust gas temperature gage is a helpful instrument for leaning the supercharged engine at cruise power with a manual mixture control.

d. Recommended standard cruise power for the supercharged engine is 65 %. At 65 % power or less this type
of engine may be leaned as desired as long as the engine operates smoothly, and temperatures and pressures are within manufacturer’s prescribed limits.

SUMMARY RECOMMENDATIONS

1. This presentation has merely covered the minimum basics of the various types of Avco Lycoming powerplants. For a more detailed description of the leaning procedures, particularly the higher powered more complex engines, refer to the Pilot‘s Operating Handbook. If the manual is incomplete, refer to Avco Lycoming Service Instruction No. 1094.

2. For maximum service life, where there is a cylinder head temperature installed, maintain cylinder head temperature (for continuous operation), below recommended 435° F (2249 C). If cylinder head temperature is higher than recommended during flight, in order to complete the flight as safely as possible, reduce head temperature to within recommended operating range by enriching the mixture, or by adjusting cowl flaps if available, or by reducing power, or by use of any combinations of these methods.

3. Some leaning during descent to traffic pattern may be in
order to prevent roughness or sudden engine cooling. The before-landing check should prevent overlooking the mixture for landing.

4. Always retum mixture to rich before increasing power.

5. Leaning the mixture in accordance with the engine manufacturer’s recommendations is practical and economical.

6. Normally aspirated, direct drive Lycoming engines operated at manufacturer’s cruise power (usually 75% power or less) may be leaned at any altitude. Do not confuse the 5,000 ft. reference for climb with this type. If cruise (for example) is 2500 ft., and 75% power or less is used, then the mixture should be leaned for all routine cruise operations outside the traffic pattern.

7. Leaning techniques vary because of differences in fuel metering devices (carburetor or fuel injector), turbocharging or supercharging, fixed pitch or constant speed prop, etc. Read the airplane Pilot's Operating Handbook and determine the proper operating technique. Get a proper check out in the aircraft.

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What people think nowadays is mostly not of interest to discuss facts.
There are tons of science and literature on the issue.
The outcome is easy: you lean to get proper fuel economy and engine longevity.

If you google “Mike Busch leaning” you will find videos and articles explaining this subject properly. Well worth the time to study them!

2.I cannot get my engine anywhere near 2249 C.

Those who pay for engine overhaul themselves should probably invest in a CHT/EGT display with individual cylinder information, a technology that has been around for decades and even shows when the first cylinder has reached peak EGT, etc. The guys who refurbished the Red Bull DC-6 have three of those per engine....

On the long run we'd better move to engine technology where this is left to electronics. We don't build new cars with chokes for quite some time already.

You'd know if you did from the iron and aluminium vapour coming out of the cowling. Your toes would probably be quite warm too.

I agree with Alpine Flyer. I can tell you that the factory engine instruments in my 182 are completely, utterly useless. There are people out there who tell you to keep CHT below 400 and even 380. I have a friend who practically declared an emergency when one CHT hit 381. Personally I try to keep them below 400 and actively keep the hottest cylinder (#3 and #4 always run hotter for some reason) below 410. That means keeping the cowl flaps open to the first notch if the OAT is warm.

One more time I say look at the manufacturers data....... not what some bloke on the Internet forum says, Lycoming have an absolute maximum CHT and a recommended don’t exceed CHT......... look them up!

A deliberate error to see if you're paying attention. ;) If you believe that I've got a bridge for sale as well. Sorry it escaped the proof reading.So what does Lycoming have to say about CHT? Here it is.


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