Aircraft-control engineering is the technology that enables pilots to be aware of the status and position of the craft they control and to determine the behavior of those craft during takeoff, flight, and landing. The field encompasses the mechanisms that govern the power plants and control surfaces of aircraft as well as communication and navigation devices.
Thrust
One of the key parameters in takeoff and flight is the amount of forward thrust delivered by an aircraft;s power plants—its engines. Some forward thrust is needed for landing, and reverse thrust may be deployed to reduce the stopping distance after an aircraft has touched down.
In the case of a propeller-driven aircraft, thrust control is achieved mainly by using control levers, or throttles, to adjust the amount of fuel delivered to the piston engines. The second factor is the pitch of the propeller blades, which is the angle from the plane of the propeller. Low pitch angles suit takeoff when airspeed is low; increased pitch is appropriate when the craft is moving rapidly through the air. Pitch may be under the pilot;s direct control through mechanical linkages, or it may be under the control of an automatic system that selects the most efficient pitch for a given flight condition. Thrust reversal for braking is achieved by reversing the pitch of the propeller blades to blow air forward.
Throttles are the principal controls of turbofan engines—the most popular power plants for passenger airliners. For thrust reversal, the pilot operates a servomechanism that drops a cowling behind the jet outlet. Once the thrust reverser is in the lowered position, thrust is increased and the hot gases escaping from the rear of the engine are directed forward to slow the aircraft.
Turbojet engines—the power plants of high-speed military jets and the Concorde—are throttled in much the same way as turbofans. They may also be operated with thrust augmentation, for which there are two methods. In the first—afterburning—fuel is injected into the hot gases near the outlet of the combustion chamber. The fuel ignites and provides more thrust as the burning gases expand. In the second, a mixture of alcohol and water is injected into the combustion chamber with an increased amount of fuel. The evaporation of water prevents the combustion chamber from overheating and increases the expansion of gas in the engine, thereby increasing thrust. Both types of thrust augmentation have controls separate from the main fuel throttles.
In all types of engines, thermocouples monitor engine temperatures and activate alarms in the case of overheating, which could be a symptom of an engine fire. On noting such an alarm, a pilot would cut the fuel supply to the affected engine and trigger its extinguishers. Other sensors detect engine rotation speeds, fuel consumption rates, and the level of fuel in the tanks. The pilot uses these readings to monitor engine performance and avoid running out of fuel.
