Page 207 - The Jet Engine

Vertical/short take-off and landing

Fig. 18-18 Reaction control system. Differential engine throttling
31. This method of control is used on multi-engined
AIRCRAFT CONTROL aircraft with the engines positioned in a suitable con-
figuration. A rapid response rate is essential to
29. The low forward speeds of V/STOL aircraft enable the engines to be used for aircraft stability
during take-off and transition do not permit the and control. It is usually necessary to combine differ-
generation of adequate aerodynamic forces from the ential throttling with differential thrust vectoring to
normal flight control surfaces, it is therefore give aircraft control in all areas.
necessary to provide one or more of the following
additonal methods of controlling pitch, roll and yaw. Automatic control systems
32. Although it is possible for the pilot to control a
Reaction controls V/STOL aircraft manually, some form of automation
30. This system bleeds air from the engine and can be of benefit and in particular will reduce the pilot
ducts it through nozzles at the four extremities of the workload. The pilot's control column is electronically
aircraft (fig. 18-18), The air supply to the nozzles is connected to a computer or stabilizer that receives
automatically cut off when the main engine swivelling signals from the control column, compares them with
propulsion nozzles are turned for normal flight or signals from the sensors that measure the attitude of
when the lift engines are shut down. The thrust of the the aircraft, and automatically adjusts the reaction
control nozzles is varied by changing their area controls, differential throttling or thrust vectoring
which varies the amount of airflow passed. controls to maintain stability.

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