This article is the result of investigations into some R22 accidents.

Disclaimer: – the following information is for use as study guidance material only.  Every possible effort has been made to establish the accuracy of the information and instructions contained on this site, however the publisher accepts no responsibility for errors or omissions and users are hereby advised that nothing contained herein must be implied, understood or applied in contradiction to any Civil Aviation Regulations or any other law of  any State, Province or Country. Pilots are to conform to the requirements of their own Company Chief Pilots, Civil Aviation regulatory Authority and the Aircraft/Engine/Component Manufacturer's Flight or Maintenance manuals. Viewers of this site use must use any information supplied at their own risk”

General Introduction

The information outlined in this presentation has been reduced to minimum essential facts, and is based on leaning the incoming fuel/air mixture as described in the Lycoming O320 “Engine Operators Manual”, and Service Instruction No. 1094.  “Fuel Mixture Leaning Procedures”.

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

1.     Basic information about fuel/air mixture leaning (Rich to Normal or Rich to Lean or Normal to Lean) needs to be available at all times.

2.     Pilots need to keep up to date with information on new helicopter models, or concerning new and improved engine instrumentation.

3.      Pilots have stated that some of the Pilot’s Operating handbooks lack sufficient information on leaning to make an informed decision about the process

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 Robinson R22 with the O-320 or O-360, have limited engine instrumentation.  Therefore, the operator requires certain basic leaning rules to protect the power plant and yet operate it efficiently.  Damage to this type of engine only results from leaning at higher than the manufacturer’s recommended cruise power of 75% max rated power.

           NOTE: The R22 Beta 2 engine is de-rated from 180 HP to 124 Hp (69% max rated power) for Max continuous use on a standard day.

           The R22 Beta 2 Max takeoff power of 131 HP is less than 75% max rated power. (Monitor the cylinder head temp gauge on take off at low DAs)

6.        The more complex power plants of higher horsepower or higher compression ratios (200 HP and higher) are generally accompanied by sufficient engine instrumentation to protect the power plants while operating at approved higher than routine power settings. The airplanes pilot’s manual will specify this information for these more complex high performance power plants. The R22 engine is not considered a complex high output engine as it is rated below 200 BHP. 

Why lean the engine (from Rich to Normal - not Rich to Lean) on my R22?

In spite of a number of variations in the different models of Lycoming power plants, there are some general recommendations on leaning offered for Lycoming piston engines except those with an Automatic Mixture Control (AMC) installed in the carburetor such as the Hiller UH12E, Bell 47 etc.

Note: Oil temperatures should run at least 74oC (165⁰ F) minimum in order to reduce moisture forming vapours and undesirable acids in the engine oil.  

 The general procedures for Leaning (rich to normal) Lycoming normally aspirated float type carburetor engines in General Aviation (the R22 fits this category) at Manufacturer’s recommended cruise power (75% or less of Max Rated Power) are:

          Float type carburetor. 

a.       Fixed pitch propeller (Fixed wing – not helicopter) – lean to a maximum increase in RPM and airspeed – or – just before engine roughness.

           b.      Controllable propeller (similar to R22 @ 104% and 15+ inches MAP – ED) – lean the mixture until roughness encountered, and then enrich slightly until roughness is eliminated and engine is smooth.

Do not attempt this procedure for the R22 helicopter in flight due the lack of a flywheel on your engine. (the rotor is not a flywheel due the effect of the "Sprague" clutch)

Only lean the R22 (from rich to normal) on the ground at normal flight ERPM (104%) before takeoff.

Engine roughness is not detonation at 75%or less Max Rated Power. It is caused by the one leanest cylinder not operating efficiently due to a very lean fuel/air mixture which will not support efficient combustion in that particular cylinder.

 c.       An Exhaust Gas Temperature gauge 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 50⁰ on the rich side of peak EGT with this type of fuel metering device.

           d.      With the application of carburetor heat, the mixture always richens.

LEANING (from Rich to normal) Recommendations for direct drive normally aspirated carbureted Lycoming engines without automatic mixture control (R22) or fuel injection.

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

 b.      In a climb from sea level through 5,000 ft. density altitude at FULL rated power (above 75% M R Power), the mixture must be full rich.  Note that the call is for density altitude - NOT altitude AMSL.

DO NOT confuse the 5,000 ft. reference for above 75% rated power climb with the cruise configuration of a de-rated engine. Simply put, R22 engine operation above 131 HP (max take off power) requires the mixture to be full rich.

Operation at higher than 75% power, without reference to cylinder head temperatures and without knowledge of specific power, requires full rich mixture. The only sure way to safely operate your engine is to utilise the Lycoming engine operator's handbook for your particular engine.  

Leaning (rich to normal) at recommended 75% or less max rated power does not damage a normal healthy engine. Leaning at higher than 75% cruise power in this type of engine can cause engine damage when complete engine instrumentation is not available (CHT and fuel flow minimum), and limitations are not spelled out in the airplane pilot’s operating handbook.

SUMMARY & RECOMMENDATIONS

1.      T This presentation has merely covered the minimum basics of the various types of low power Textron Lycoming power plants.  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 Textron Lycoming Service Instruction No. 1094.

2.      F  For maximum service life, maintain cylinder head temperature (for continuous operation), below recommended 435⁰ F (224⁰ 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 reducing power, or by use of any combinations of these methods.

3.         During descent to traffic pattern, the mixture may be richened if the landing is at a lower DA than the takeoff. The before – a pre landing check should consider the mixture required for landing.

 Always return the mixture to rich before increasing power above 75%.

5.         Leaning the mixture to normal 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 M R P) may be leaned at any altitude.  Do not confuse the 5,000 ft. reference for climb with this type.   If ,for example, you are operating your R22 at 2500 ft. at under gross weight and 75% power or less M R P (131 HP for the R22) is used for the hover, then the mixture should be leaned (rich to normal) for all routine operations outside the traffic pattern.

7.       L  Leaning techniques vary for different aircraft types because of differences in fuel metering devices (carburetor or fuel injector), turbo - charging or super - charging, fixed pitch or constant speed prop, etc.  Read the airplane Pilot’s Operating Handbook and determine the proper operating technique. Use Lycoming Service Instruction 1094 if nil flight manual data. Nothing beats a proper check out in the aircraft at high density altitude.

Addendum:

The R22 carb often is set on a lean bias. Leaning (from Rich to Normal) is usually only effective when ambient temperatures are ABOVE ISA or operating at higher altitudes.

.