9 ECONOMIC OPERATION
Each member shall operate the aircraft with due concern for the costs incurred by his or her methods of handling and operating the aircraft.
Note: The information contained in this section regarding our engines and how to care for them comes from the Lycoming Flyer Key Reprints documents (Lycoming, 2011). The recommendations of the Pilot’s Operating Handbook (POH) provide the best guidance for operation of an aircraft/engine combination, and therefore the recommendations and limitations of the POH should also be observed.
9.2 General Engine Operation Rules
9.2.1 Temperature Limits
Without exception, observe the redline temperature limits during takeoff, climb and high-performance cruise power operation. If you are unsure how to cool an engine in flight, ask one of the club CFIs or maintenance officers for further clarification and instruction.
9.2.2 Leaning Below 5000ft Density Altitude
The oft-quoted figure of 5000 feet is based on the engine being unable to produce more than 75% power, even at full throttle, at that altitude. Cruise power for Lycoming normally aspirated engines is generally considered to be 55% to 75% of the maximum power for which the engine is rated. At these reduced power settings, the engine may be leaned at any altitude.
There has been confusion amongst pilots in general about the reference to not leaning below 5000-feet density altitude. Remember that this reference only applies to those power settings above the cruise range — those normally used for takeoff and climb. Once cruise power has been set, leaning to best economy should be standard procedure as damage to the engine will not occur from leaning at cruise power settings.
9.2.3 Mixture Adjustment
Whenever mixture is adjusted, rich or lean, it should be done slowly.
9.2.4 Mixture Full Before Power Increase
Always return mixture slowly to full before increasing power setting.
9.2.5 Temperature Change
At all times, caution must be taken not to shock-cool the cylinders. The maximum recommended temperature change should not exceed 50° F per minute.
9.2.6 Maximum Service Life
For maximum service life, maintain the following recommended limits for continuous cruise operation:
- Engine power setting – 65% of rated or less;
- Cylinder head temperature – 400° F. or below;
- Oil temperature - 165° F - 220° F.
9.2.7 Lean of Peak (LOP)
Operating on the lean side of peak EGT can only be accomplished with fuel-injected engines of at least 250 HP or higher AND a complete set of reliable engine instruments to protect the engine because the fuel flows in the lower horsepower engines are so small. It isn’t possible with float-type carburetors because of imperfect fuel/air distribution. In any case, leaning past the peak is not recommended.
9.3 Power Settings
Operating our high-performance aircraft at minimum RPM and maximum MP within the allowable envelope as defined in the POH helps our engines last longer. Low RPM operation provides numerous benefits, such as better cylinder compression, lower frictional losses, improved propeller efficiency, cooler-running valves, lower EGTs and CHTs, and a quieter cabin. The combinations of RPM and MP listed in the cruise power charts of the airframe POH have been flight tested and approved by the airframe and power plant engineers. Therefore, if there are power settings such as 2100 RPM and 24" MP in the power chart, they are approved for use. Lycoming recommends the pilot attempt the various combinations offered by the power chart over a five-minute period when flying in smooth air, and use the listed RPM and MP combinations which give the least vibration and the lowest noise level.
9.4 Engine Temperature Management
The best way to manage our piston engines is by limiting temperature. By keeping large engine temperature changes over a short period of time to a minimum, and within prescribed limits, the safety, reliability and longevity of our engines are significantly enhanced.
As a rule, the pilot should keep engine temperatures at settings that maximize engine life. Engine experts suggest an oil temperature of around 180° F or a little higher for typical air-cooled GA engines. If the aircraft is equipped with a cylinder head temperature (CHT) gauge, the CHT should not be allowed to exceed 380-400° F.
There are two ways to control engine temperature: fuel flow (throttle and mixture) and airflow (pitch attitude and cowl flaps, if the aircraft is so equipped). On hot days, the pilot may need to enrich the mixture, open cowl flaps, lower the nose, or even reduce power to keep CHTs within limits. If the aircraft has cowl flaps, which increase the amount of air flowing over the engine, the pilot should leave them open even after leveling off until temperatures stabilize – then close them as appropriate. Hot summer days in the desert most likely require keeping the cowl flaps open even after established in cruise flight.
Also, check for any induced drag. Be sure flaps are fully retracted, landing gear retracted, and correct pitch trim after established in cruise and prior to engaging altitude hold – if equipped. Indications on the Comanche and Skylane autopilot will tell you of consistent nose up or down commands. Manually establishing the aircraft in straight-and-level flight before engaging the autopilot altitude hold will extend the life of the servos.
9.5 Mixture Leaning
Leaning procedures vary considerably between aircraft. Regardless of the fuel-metering device, fuel management of normally aspirated engines is primarily dependent on the instrumentation available. The method is the same for both fixed- and controllable- pitch propellers. All Club aircraft have at a minimum an exhaust gas temperature gauge to assist in leaning. The high-performance aircraft also have cylinder head temperature and fuel flow gauges that allow a greater degree of accuracy. It is important that you are familiar with the correct flight manual and engine manufacturer’s leaning procedure for the aircraft you fly.
9.5.1 Density Altitude
For 5,000 feet density altitude and above, or high ambient temperatures, roughness or reduction of power may occur at full rich mixture. The mixture may be adjusted to obtain smooth engine operation. For fixed-pitch propellers, lean to maximum RPM at full throttle prior to takeoff where airports are at 5,000-feet density altitude or higher. With fuel injection, if the power plant has a marked fuel-flow gauge, the mixture should be set in accordance with instructions on the fuel-flow gauge and/or in accordance with the aircraft POH. Limit operation at full throttle on the ground to a minimum.
9.5.2 Taxi Operations
Over leaning isn’t a problem when running at just above idle power during ground operations. During a long taxi or a lengthy wait for takeoff clearance, the engine can be leaned aggressively without the risk of damage. Leaning on the ground helps prevent spark plug fouling.
Use full-rich mixture during takeoff or climb. Careful observation of engine temperature instruments should be practiced to ensure the limits specified are never exceeded. Refer to the aircraft POH for more specific instructions.
9.5.4 Cruise Flight
The mixture should always be leaned during cruise provided that the desired altitude will be maintained for a reasonable period of time. The engine can be leaned at any altitude provided the power setting is 75% or less. A properly leaned engine can significantly increase the still-air range of an aircraft compared with not leaning at all at the same altitude.
- Best Economy Cruise – Peak EGT
- Best Power Cruise - 100° F Rich of Peak EGT (Skylane 125° F)
Lycoming has long authorized leaning to peak EGT at any cruise setting up to 75% power. Where cylinder head temperature is also available, the pilot should always cross-check the head temperature as a routine procedure when leaning, and remember that whenever CHT reaches the maximum before reaching peak EGT, then CHT rather than EGT should dictate the limit of allowable leaning.
Regardless of the field elevation where the pilot intends to land, the descent from cruise altitude to traffic pattern altitude should be made with the engine leaned for smooth engine operation. Low elevation fields (below 5,000 feet density altitude) will require that the mixture be moved to full rich in the “before landing checklist.” Landing at airports above 5,000 feet density altitude, the mixture must be leaned to smooth engine operation during traffic pattern flight and landing, otherwise the engine may stop on the runway because of excessive richness.
9.6 Engine Preheat
During mostly warm desert climate flying, engine preheat is not something that concerns pilots; however, during the desert winter or when flying from one climactic zone to another, temperature changes can be extreme. If the aircraft was parked outside overnight and the temperature is below 20°F, the engine should be preheated, both to aid in starting and prevent engine damage. During a cold start, try to avoid draining the battery unnecessarily. Leave avionics, electric flaps, and aircraft lighting, which all rely on and use battery power, off until the engine is running.
Different metals in the engine will shrink at varying rates and parts clearances can become extremely small below 20°F. Oil loses some ability to lubricate at extremely low temperatures. Starting an engine in these conditions can cause metal parts to rub together and cause extreme wear in a very short time. Preheating helps prevent this wear and also helps fuel vaporize more easily for quick starting.
When using a hot-air preheater, plug the air intakes on either side of the propeller and place a blanket over the cowling to contain the heated air. Preheat for 15 to 20 minutes to ensure even heating for the entire engine.
9.7 Brakes & Tires
- Do not ride the brakes during taxi. Use minimum power and speed necessary for taxi operations.
- Avoid unnecessary heavy braking on the landing roll.
- At the discretion of the Board, any pilot who abuses aircraft brakes or tires may be charged for their replacement.