Stall warning system

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Acoustic warning signal of the stall warning system of a Piper PA-28
Metal tongue on the wing leading edge of a Piper PA-28
Vacuum hole on the wing leading edge of a Diamond DV-20 Katana

The stall warning system is a safety system in aircraft . It warns the pilot of an impending stall due to stalling during the flight .


Schematic representation of a stall warning system using a metal tongue

A stall occurs when the angle of attack of the wing rises above the critical level. For many general aviation aircraft , this angle is between 16 and 18 degrees. A stall warning system detects this condition and triggers an optical , acoustic or haptic warning. The manufacturer's specifications require that the warning system reacts at 1.1 times the stall speed . The functionality of the system is checked during the annual inspection. For most aircraft, the functionality check is also part of the pre-flight checklist .

Smaller machines use, among other things, a resonance pipe or horn in the cockpit that is directly connected to a borehole in the wing. The borehole is located on the leading edge of the wing and is oriented forward in level flight. If the angle of attack increases, the orientation of the hole to the air flow changes. At the critical point, the air flow sweeps over the hole. A negative pressure is created , air flows out of the hole and the horn is triggered. This design works purely pneumatically and does not require a power supply. It is used, for example, on the Diamond DV-20 Katana .

Another possibility is a hinged metal tongue attached to the nose area of ​​the wing. In normal flight, the metal tongue is pressed against its lower stop by the flow. If the angle of attack rises above the critical point, the metal tongue is hit from below, snaps and is pushed upwards. The warning for the excessive flight condition is then triggered in the cockpit via an electrical contact. This variant is used, for example, in the Piper PA-28 .

The warning is issued to the pilot acoustically via a warning horn ( "stall horn" ), an automated announcement voice, often also warning lamps, the warning is shown in the primary flight displays on larger aircraft and haptically as a clearly perceptible vibration in the conventional steering column ( “stick shaker” ) or as a synthetically generated counterforce in sidesticks . Often, depending on the aircraft type and the degree of digitization of the flight control, the triggering of the stall warning generates automatic actions by assistance systems, such as the complete or partial deactivation of the autopilot depending on the type and execution of automatic control inputs that are intended to help the pilot in avoiding or eliminating the dangerous situation ( "stick pusher " ).

supporting documents

  • Stall warning. Article in aero kurier, November 2013, accessed April 20, 2018 .

Individual evidence

  1. Flight manual Diamond DV-20 Katana . Diamond Aircraft , 1999.
  2. Flight manual Piper PA-28 . Piper Aircraft , 1995 (English).
  3. Aaron Boone: CRJ 700 Aircraft Systems Study Guide . A. Boone, 2013, ISBN 978-0-9790767-3-2 , pp. 106 (English, ).