Aviation Learning Center Document Engine Operation for Pilots - P-8740-13
Author: Teledyne Continental and AVCO Lycoming Date: unknown
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Introduction
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Unless you are flying a glider, the aircraft engine is one of the most important parts of your aircraft. Knowing how to operate your engine in accordance with the manufacturer's recommendations is one of the most important things you can do to ensure your safety in the air. This document provides information and basic tips for safe engine operations in general aviation aircraft.

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Safe Engine Operations
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Proper Preflight

  • Use the correct amount and grade of aviation gasoline. Never use auto gas or jet fuel in aircraft piston engines.

  • Use the correct grade and amount of oil in your engine. Generally, engines use SAE 50 above 40 degrees Fahrenheit; and SAE 30 or 10W30 below 40 degrees Fahrenheit.

  • In cold weather make sure that the engine oil is sufficiently warm before starting the engine. Below 20 degrees Fahrenheit, use a heated hangar or preheat.

  • Drain the fuel sumps to assure there is no water or foreign matter in the fuel system.

  • Make certain cooling air inlets are open and free of foreign objects (bird's nests, etc.)

  • Ensure that the oil cap and dipstick are properly secured. Check for obvious oil and fuel leaks.

Starting and Warm-Up

In normal and hot weather:

  • Little or no priming is necessary.
  • Make runups thorough, but as brief as possible. To minimize spark plug fouling, idle engine at 1000 to 1200 rpm.
  • Avoid overheating by keeping ground operations to a minimum. Park and complete runup into the wind.
  • Cowl flaps should be open for all ground operations.

In cold weather:

  • Make sure magnetos and master switch are "off," then rotate propeller by hand about six revolutions before attempting to start engine.
  • Prime engine as recommended in the Pilot's Operating Handbook. Avoid over priming.
  • Oil pressure should be in the green arc range within 60 seconds. If it is not, shut down and investigate.
  • Operate engine at 1000 rpm until oil pressure is in the green arc range and steady. Fluctuating oil pressure means that cavitation is occurring. Shut down and use additional preheat.
  • If equipped with a constant speed propeller, cycle it several times to fill the propeller hub with warm oil. (Refer to your Pilot's Operating Handbook for specifics.)

Take-off and Climb

  • Follow your checklist.
  • Use full throttle (with few exceptions).
  • Mixture full rich, except at high density altitude airports where you should lean as appropriate. (Refer to your Pilot's Operating Handbook for specifics.)
  • Use 75 percent power for climb.
  • Climb at higher than normal airspeeds on hot days to improve engine cooling.
  • Lean the mixture during climb to the specified fuel flow or for smooth operation above a density altitude of 5000 feet.

Cruise

  • Set 65 to 75 percent power for best performance.
  • Set 55 percent power for best economy and range.
  • Lean the engine in accordance with the instructions in the Pilot's Operating Handbook for your specific aircraft.

Descent and Landing

  • Avoid overcooling. Maintain sufficient power to keep engine temperatures in the green arc range.
  • Gradually enrichen the mixture for smooth engine operations as you descend.
  • Keep cowl flaps closed.
  • Set mixture to full rich before landing, unless you are landing at a high density altitude airport. For operation into and out of high altitude airports, consult the Pilot's Operating Handbook for your specific aircraft.

Use of Carburetor Heat

  • Carburetor heat should be used whenever atmospheric conditions indicate that icing is a possibility, and when the engine is operated at or below 75 percent power.
  • When using carburetor heat, always use full heat.
  • After applying carburetor heat, lean the mixture for smooth operation. The warm intake air is less dense, and produces a richer mixture.

Summary

  • Follow the Pilot's Operating Handbook procedures for your specific aircraft, and "know'em cold."
  • Comply with all engine and airframe manufacturer service bulletins, letters, etc.
  • Use your checklist.
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Leaning for Direct-Drive, Normally-Aspirated Engines
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Definitions

  • Direct drive means that the propeller is bolted to, and turns at the same speed as, the crankshaft. No reduction gearing is used.
  • Normally aspirated means that the engine has no supercharger or turbocharger to maintain sea level atmospheric pressure at higher altitudes and, therefore, that its maximum available power decreases with altitude.

Theory

Fuel flow through either a carbureted or fuel injected induction system must be adjusted manually, in almost all instances, to provide for the most efficient fuel to air ratio for efficient combustion within the cylinders. Given certain fuel to air mixtures, it is possible to have a situation where the engine will run rough or will not run at all. Since air density varies with temperature and altitude, it is important to understand when and how to adjust the mixture control to obtain the best performance, fuel economy and maximum life from your engine. A key point to understand is that here is an optimum fuel to air mixture setting at which to achieve either "best economy" cruise or "maximum power."

Why Lean?

You should lean the mixture for:

  • Improved engine efficiency.
  • Greater fuel economy (i.e., minimum specific fuel consumption) and longer range.
  • Smoother engine operation - saves engine accessories and engine mounts.
  • Longer spark plug life, less fouling.
  • Reduced maintenance costs.
  • Reduced operating costs.
  • More desirable engine temperatures while operating at cruise altitudes.

When to Lean

  • Lean anytime the power setting is 75 percent or less at any altitude. (Full throttle or climb power through 5000 feet density altitude usually means mixture full rich.)
  • At high altitude airports, lean for taxi, take-off, traffic pattern entry and landing.
  • For landings at airports below 5000 feet density altitude, adjust the mixture for descent, but only as required. You can't go wrong if you keep the engine running smoothly!
  • Before entering the traffic pattern, go to full rich.

Always consult the Pilot's Operating Handbook for your specific aircraft for the proper leaning procedures.

How to Lean

  • Tachometer Method (for use with fixed or variable pitch propellers): Set the controls for the desired cruise power setting as shown in the POH. Then gradually lean the mixture from full rich until the tachometer reading peaks. In smooth air, you should also notice a slight increase in aircraft speed. At peak RPM, the engine is operating within the maximum power range. For best economy operation, the mixture is first leaned from full rich to maximum power, then the leaning process is slowly continued until the engine starts to run rough. Then, enrich the mixture sufficiently to obtain a smooth firing engine. Obviously, some engine power and airspeed is sacrificed when operating at best economy. What you gain, however, is increased endurance.

  • Engine "Rough" Method (for use with fixed or variable pitch propellers and engines equipped with float-type carburetors only): With this method, first set the throttle to the appropriate power setting, (75 percent power or less). Lean the engine gradually until the engine starts to run rough; then enrichen the mixture slightly until the engine is again running smoothly. You will then be operating near the "best economy" mixture setting.

  • Fuel Flow Indicator Method (for use with any type propeller): The POH for aircraft equipped with fuel flow gauges contains appropriate fuel flow settings or, alternatively, the fuel flow gauge may be marked for correct flow at each power setting. You need only lean the mixture to the published or marked fuel flow values to achieve the correct mixture.

  • Exhaust Gas Temperature (EGT) Method (for use with any type propeller): Peak EGT occurs essentially at the rich edge of the best economy mixture range. Operation at peak EGT not only provides essentially minimum specific fuel consumption but also 95 to 96 percent of the engine's maximum power capabilities for a given engine speed and manifold pressure. In addition, engine operation is very smooth at peak EGT. In comparison, a very noticeable power loss or roughness will occur when the engine is operated at the lean side of the best economy range.

High Altitude Operations:

At high altitude airports (5000 feet density altitude and above), lean for taxi, takeoff, descent and landing. Use the following procedures:

  • Startup and Taxi: Lean at 1000 RPM (all propeller combinations) until RPM peaks, then enrichen slightly.
  • Before Takeoff: Go to full throttle and lean mixture. With a fixed pitch prop,lean to maximum RPM and then enrichen slightly. With a variable pitch prop on carbureted engines, lean to engine smoothness. If you have an EGT gauge, lean to +100 degrees F. on the rich side of peak. With fuel-injected engine, lean to the correct fuel flow setting according to the POH for your specific airplane.
  • Traffic Pattern Ops: Always lean at traffic pattern altitude for landing at high altitude airports, but only after you have established maximum power. This practice will ensure maximum available power in the event that you need to make a go-around.
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Review of Leaning Procedures
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The chart below summarizes leaning procedures for various propeller/EGT/fuel flow indicator (FFI) combinations.

used for alignment Leaning Procedures Summary used for alignment
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used for alignment Type of Prop  EGT  FFI  Leaning Method used for alignment
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used for alignment Variable  No  No  "Engine Rough" used for alignment
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used for alignment Fixed/Variable  No  No  Tachometer or "Engine Rough" used for alignment
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used for alignment Fixed/Variable  No  Yes  POH settings or as marked on FFI used for alignment
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used for alignment Fixed/Variable  Yes  No  Use POH to set EGT (usually to peak); enrichen until engine runs smooth used for alignment
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used for alignment Fixed/Variable  Yes  Yes  Use POH to adjust FF; lean by setting EGT per POH used for alignment
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Always follow the engine operating procedures provided by the aircraft manufacturer for your aircraft in the Pilot's Operating Handbook.

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About This Series
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The purpose of this series of Federal Aviation Administration (FAA) Aviation Safety Program publications is to provide the aviation community with safety information that is informative, handy, and easy to review. Many of the publications in this series summarize material published in various FAA advisory circulars, handbooks, other publications, and various audiovisual products developed by the FAA and used in its Aviation Safety Program.

Some of the ideas an materials in this series were developed by the aviation industry. The FAA acknowledges the support of the aviation industry and its various trade and membership groups in the production of this series.

Comments regarding these publications should be directed to the National Aviation Safety Program Manager, Federal Aviation Administration, Flight Standards Service.

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