Stick pusher
Encyclopedia
A stick pusher is a device installed in some fixed-wing aircraft
to prevent the aircraft from entering an aerodynamic stall
. Some large fixed-wing aircraft display poor post-stall handling characteristics or are vulnerable to deep stall. To prevent such an aircraft approaching the stall the aircraft designer may install a hydraulic or electro-mechanical device that pushes forward on the elevator
control system whenever the aircraft’s angle of attack
reaches the pre-determined value, and then ceases to push when the angle of attack falls sufficiently. A system for this purpose is known as a stick pusher.
The safety requirements applicable to fixed-wing aircraft in the transport category
, and also to many military aircraft, are very demanding in the area of pre-stall handling qualities and stall recovery. Some of these aircraft are unable to comply with these safety requirements relying solely on the natural aerodynamic qualities of the aircraft. In order to comply with the requirements aircraft designers may install a system that will constantly monitor the critical parameters and will automatically activate to reduce the angle of attack when necessary to avoid a stall. The critical parameters include the angle of attack, airspeed
, wing flap setting and load factor. Action by the pilot is not required to recognise the problem or react to it.
Aircraft designers who install stick pushers recognise that there is the risk that a stick pusher may activate erroneously when not required to do so. The designer must make provision for the flight crew to deal with unwanted activation of a stick pusher. In some aircraft equipped with stick pushers, the stick pusher can be overpowered by the pilot. In other aircraft, the stick pusher system can be manually disabled by the pilot.
Stick pushers should not be confused with stick shaker
s. A stick shaker is a stall warning device whereas a stick pusher is a stall avoidance device.
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
to prevent the aircraft from entering an aerodynamic stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
. Some large fixed-wing aircraft display poor post-stall handling characteristics or are vulnerable to deep stall. To prevent such an aircraft approaching the stall the aircraft designer may install a hydraulic or electro-mechanical device that pushes forward on the elevator
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...
control system whenever the aircraft’s angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
reaches the pre-determined value, and then ceases to push when the angle of attack falls sufficiently. A system for this purpose is known as a stick pusher.
The safety requirements applicable to fixed-wing aircraft in the transport category
Transport category
Transport category is a category of airworthiness applicable to large civil airplanes and large civil helicopters. Any aircraft's airworthiness category is shown on its airworthiness certificate...
, and also to many military aircraft, are very demanding in the area of pre-stall handling qualities and stall recovery. Some of these aircraft are unable to comply with these safety requirements relying solely on the natural aerodynamic qualities of the aircraft. In order to comply with the requirements aircraft designers may install a system that will constantly monitor the critical parameters and will automatically activate to reduce the angle of attack when necessary to avoid a stall. The critical parameters include the angle of attack, airspeed
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
, wing flap setting and load factor. Action by the pilot is not required to recognise the problem or react to it.
Aircraft designers who install stick pushers recognise that there is the risk that a stick pusher may activate erroneously when not required to do so. The designer must make provision for the flight crew to deal with unwanted activation of a stick pusher. In some aircraft equipped with stick pushers, the stick pusher can be overpowered by the pilot. In other aircraft, the stick pusher system can be manually disabled by the pilot.
Stick pushers should not be confused with stick shaker
Stick shaker
A stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke of an aircraft to warn the pilot of an imminent stall...
s. A stick shaker is a stall warning device whereas a stick pusher is a stall avoidance device.
See also
- British European Airways Flight 548British European Airways Flight 548British European Airways Flight 548 was a Hawker Siddeley Trident 1C airliner, registration G-ARPI, operating as a British European Airways scheduled commercial passenger flight from London Heathrow Airport to Brussels, Belgium...
- Continental Connection Flight 3407