Stick shaker
Encyclopedia
A stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke
(the "stick") of an aircraft to warn the pilot of an imminent stall
. It is connected to the control column of most business jet
s, airliner
s and military aircraft.
The stick shaker is a component of the aircraft's stall protection system, which is composed of wing-mounted angle of attack
sensors that are connected to an avionics computer. The computer receives input from the AOA sensors and a variety of other flight systems. When the data indicate an imminent stall condition, the computer actuates both the stick shaker and an auditory alert.
The shaker itself is composed of an electric motor connected to a deliberately unbalanced flywheel. When actuated, the shaker induces a forceful, noisy, and entirely unmistakable shaking of the control yoke. This shaking of the control yoke matches the frequency and amplitude of the stick shaking that occurs due to airflow separation in conventional aircraft as they approach the stall. The stick shaking is intended to act as a backup to the auditory stall alert, in cases where the flight crew may be distracted.
In larger aircraft (especially in T-tail
ed jets that might be vulnerable to deep stall), some stall protection systems also include a stick pusher
system to automatically push forward on the elevator
control, thus reducing the aircraft's angle of attack
and preventing the stall. Both systems have to be tested and armed before takeoff and remain on during flight.
The vibration of the stick shaker is often heard on black box
recordings of aircraft that entered a stall condition prior to a crash.
Yoke (aircraft)
A yoke, alternatively known as control column, is a device used for piloting in most fixed-wing aircraft.- Principle :The aviator uses the yoke to control the attitude of the plane, usually in both pitch and roll. Rotating the control wheel controls the ailerons and the roll axis...
(the "stick") of an aircraft to warn the pilot of an imminent 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...
. It is connected to the control column of most business jet
Business jet
Business jet, private jet or, colloquially, bizjet is a term describing a jet aircraft, usually of smaller size, designed for transporting groups of up to 19 business people or wealthy individuals...
s, airliner
Airliner
An airliner is a large fixed-wing aircraft for transporting passengers and cargo. Such aircraft are operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an aircraft intended for carrying multiple passengers in commercial...
s and military aircraft.
The stick shaker is a component of the aircraft's stall protection system, which is composed of wing-mounted 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...
sensors that are connected to an avionics computer. The computer receives input from the AOA sensors and a variety of other flight systems. When the data indicate an imminent stall condition, the computer actuates both the stick shaker and an auditory alert.
The shaker itself is composed of an electric motor connected to a deliberately unbalanced flywheel. When actuated, the shaker induces a forceful, noisy, and entirely unmistakable shaking of the control yoke. This shaking of the control yoke matches the frequency and amplitude of the stick shaking that occurs due to airflow separation in conventional aircraft as they approach the stall. The stick shaking is intended to act as a backup to the auditory stall alert, in cases where the flight crew may be distracted.
In larger aircraft (especially in T-tail
T-tail
thumb|right|Grob motor gliderA T-tail is an aircraft tail stabilizer configuration in which the horizontal surfaces are mounted to the top of the vertical stabilizer. Traditionally, the horizontal control surfaces are mounted to the fuselage at the base of the vertical stabilizer...
ed jets that might be vulnerable to deep stall), some stall protection systems also include a stick pusher
Stick pusher
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...
system to automatically push 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, thus reducing 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...
and preventing the stall. Both systems have to be tested and armed before takeoff and remain on during flight.
The vibration of the stick shaker is often heard on black box
Black Box (transportation)
The term black box is a placeholder name used casually to refer to a collection of several different recording devices used in transportation: the flight recorders in aircraft, the event recorder in railway locomotives, the event data recorder in automobiles, message case in ships, and other...
recordings of aircraft that entered a stall condition prior to a crash.