Throttle Control
The throttle control allows the pilot to control engine power. The throttle is connected to the throttle valve on a carburetor or to the fuel/air control device on a fuel injected engine.
Moving the throttle control forward increases engine power, while moving it rearward results in lower engine power.
Propeller Control
When an airplane has an adjustable pitch propeller, the propeller control is connected to the propeller governor. The governor adjusts the pitch of the propeller in order to maintain a specific engine speed, measured in revolutions per minute (RPM).
Moving the propeller control forward sets the propeller pitch for high engine RPM, while moving the propeller control rearward sets the propeller pitch for lower engine RPMs. As engine power and load vary, the propeller governor varies the pitch of the propeller to maintain the set RPM.
High RPM settings are used for high power, low airspeed operations, such as takeoff, initial climb, and go-around. The propeller is set for lower engine RPMs during cruise, in order to improve fuel economy and increase cruising speed. Manipulating the propeller control is roughly equivalent to changing gears in a car.
Airplanes with fixed pitch propellers do not have a propeller control.
Mixture Control
The fuel and air must be combined in the correct ratio in order to burn efficiently inside the engine. If there is too much fuel or too much air, the engine will not run at its best.
As you go higher and higher in the atmosphere, you encounter thinner and thinner air. The mixture control is provided to allow the pilot to thin the fuel to the engine to match this thinner air.
In the forward position, the mixture is set for sea level. This setting is used for takeoff, landing, and operations at lower altitudes. This forward position is called the rich position. As the airplane gains altitude with the mixture control in the full rich position, the engine is provided with enough fuel to match sea level air pressure. As a result, the mixture becomes richer and richer as the air becomes less and less dense at higher altitudes.
Moving the mixture control rearward leans the fuel/air mixture by reducing amount of fuel being mixed with the air. Leaning techniques vary among engines and airplane owners. The engine may be leaned until the engine produces the highest RPM or adjusted to achieve a desired exhaust gas temperature, as measured by an exhaust gas temperature gauge. The purpose of leaning the mixture remains the same, however, to decrease fuel flow in order to compensate for decreased air density at altitude.
During the descent, the pilot must remember to return the mixture control to the rich position. If you were to lean the airplane at an altitude of 9,500 feet, then descend to a lower altitude without adjusting the mixture, the fuel/air mixture will become excessively lean.
The mixture control is also used to shut down the engine. Moving the mixture control to the cut-off position starves the engine of fuel and the engine dies. This method of engine shut down allows for the safe handling of the airplane on the ground. If the engine were stopped by placing the ignition switch to off, as a car engine is shut down, the engine would be ready to fire. By starving the engine of fuel with the mixture control, the pilot has created a situation in which the engine is not likely to fire if the propeller is moved, even if the ignition wiring is damaged or faulty. Unlike a car, the airplane's ignition system is powered anytime the engine turns. The ignition switch and wiring merely prevent the firing of the spark plugs.
Enriching the mixture also aids in engine cooling. If the engine is running too hot, enriching the mixture can aid in solving the problem.
Runup and Takeoff at High Airport Elevation
The fuel/air mixture is also leaned prior to takeoff at high elevation airports. Follow the procedures recommended by your aircraft manufacturer and flight instructor. usually, high elevation airports are considered to be those with a field elevation greater than 5,000 feet above sea level. The pilot normally conducts a full power engine run-up to properly lean the engine before takeoff. This ensures the best engine power is available for takeoff at the higher field elevation.
At higher field elevations, the pilot usually conducts the run-up with a leaned mixture, as well. With a full rich mixture, engine roughness may occur during the run-up. The pilot might confuse this engine roughness for some other engine problem and cancel the flight without cause. If you encounter engine roughness during the run-up at higher altitudes, try with a leaner mixture and see if it solves the problem.
Engine Control Colors and Shapes
Each engine control has its own shape and color. This allows the pilot easy, quick recognition of the correct engine control. The shape of the controls allow a pilot to recognize the engine control by its feel.
The throttle control is colored black. The propeller control is blue, and the mixture control is red.