Aircraft engine controls

Aircraft engine controls provide a means for the pilot to control and monitor the operation of his aircraft's powerplant. This article describes controls used with a basic internal-combustion engine driving a propeller. Some optional or more advanced configurations are described at the end of the article. Jet turbine engines use different operating principles and have their own sets of controls and sensors.

Basic Controls and Indicators

Main Power Switch - Connects the output of the Alternator, or Battery, or both to the power distribution bus.
Throttle - Sets the desired engine power level. The Throttle controls the volume of fuel/air mixture delivered to the cylinders.
Mixture Control - Sets the amount of fuel added to the intake airflow. At higher altitudes the air pressure declines so the fuel volume must also be reduced. This process is known as "leaning".
Ignition Switch - Connects the magnetos to the spark plugs and optionally runs the starter motor. The Ignition Switch has the following positions:
1. Off - Both magnetos are connected to electrical ground.
2. Left - The left magneto is connected to its spark plugs. The right magneto is grounded.
3. Right - The right magneto is connected to its spark plugs. The left magneto is grounded.
4. Both - Both magnetos are connected to their spark plugs. This is the normal operating configuration.
5. Start - The pinion gear on the starter motor is engaged with the flywheel and the starter motor runs to turn the engine over.
Tachometer - A gauge to indicate engine speed in revolutions per minute (R.P.M.).
Oil Temperature Gauge - Indicates the operating temperature of the engine.
Oil Pressure Gauge - Indicates the supply pressure of the engine lubricant.
Carburetor Heat Control - Applies heat to the carburetor venturii area to remove or prevent the formation of ice in the throat of the carburetor.

Fuel

Fuel Primer Pump - A manual pump to add a small amount of fuel at the cylinder intakes to assist in starting a cold engine.
Fuel Quantity Gauge - Indicates the amount of fuel remaining in the identified tank. One per fuel tank.
Fuel Select Valve - Connects the fuel flow from the selected tank to the engine.

If the aircraft is equipped with a fuel pump

Fuel Pressure Gauge - Indicates the supply pressure of fuel to the intake manifold.
Fuel Boost Pump Switch - Controls the operation of the auxilliary electric fuel pump to provide fuel to the engine before it starts or in case of failure of the engine powered fuel pump.

Propeller

If the aircraft is equipped with adjustable-pitch (constant-speed) propeller

Propeller Control - Sets the desired R.P.M. of the propeller by adjusting the angle-of-attack, or pitch, of the blades.
Manifold Pressure Gauge - Indicates the differential in pressure between the outside air and the engine's intake manifold. Higher power levels cause a larger pressure drop.

Cowl

If the aircraft is equipped with adjustable Cowl Flaps

Cowl Flap Position Control - Cowl Flaps are opened during high power/low airspeed operations like takeoff to maximize the volume of cooling airflow over the engine's radiator fins. They are closed during normal cruise flight to maintain normal engine operating temperature and minimize drag.
Cylinder Head Temperature Gauge - Indicates the temperature of the cylinder with the least cooling airflow. A Cylinder Head Temperature Gauge has a much shorter response time than the oil temperature gauge so it can be used to fine tune the engine's power output. Engine overheating may be caused by
1. Running too long at a high power setting.
2. Running too lean on the fuel mixture.
3. Restricting the volume of cooling airflow too much.
4. Insufficient delivery of lubricating oil to the engine's moving parts.

References

Private Pilot Manual; Jeppesen Sanderson; ISBN 0-88487-238-6 (hardcover, 1999)