Anyone know how stall indicators on full scale airplanes work?

I.E. how do they determine the aircraft is approaching a stall? Do they simply monitor a certain airspeed and/or angle of attack, or do they go beyond that an actually monitor lift vs wing loading, etc?

not too complicated on puddle jumpers. perhaps a search using google will be more fruitful and satisfying but i know cessna uses one system and piper another. airflow over the wings and separation at the leading edge causes some "cool" effects; in one case, it's used to vibrate a reed to let you know of an imminent stall. like i said, a more indepth explanation can be had by googling your question.

thanks for the info, starwoes...actually, I HAD tried googling it, and am usually pretty good at finding what I want...but in this case, i struck out. May just have to keep looking.

http://www.av8n.com/how/htm/airfoils...sec-stall-wrng

Since an airplane can be stalled at any airspeed, a stall indicator referencing airspeed alone would not be an altogether reliable means of determining an impending stall condition. AOA (angle of attack) is the critical component of an imminent stall situation, and as such most aircraft use a means of alerting the pilot when this AOA is reached. Various techniques are employed: Leading edge orifices, tabs, and fuselage mounted AOA vanes are some of the more common methods.

The article referenced by Kuga220 is a very good description of how the stall warning device works on typical light aircraft.

It should be noted that the warning device doesn’t indicate a stall but gives a warning that a stall is imminent. FAR part 23 under which such aircraft are certified requires the warning “…..to begin at a speed exceeding the stalling speed by not less than five, and not more than ten miles per hour, and must continue until the stall occurs.” The vane type like used on the piper is an on-off switch. However the suction type as used on the Cessnas begins with a subtle noise that increases in pitch and intensity until the stall occurs, giving some indication of margin above stall. Neither gives indication of AOA directly and are less useful in accelerated flight.

Good stuff, guys! Thanks!

It works off of pressure. In a cessna, there is a small hole in the wing, when the air on the bottom of the wing slows to the same speed as the top of the wing, it creates a vacuum, witch activates the buzzer. you test it by sucking on that hole...

alot of good info here. and the far does state the warning must be before stall speed however you can set it to go off below stall speed (i mean its possible not legal). aoa vanes tied to a air data computer will do wonders now the adc (air data computer) knows the speed of the aircraft pitot and static are also tied into the adc plus with the aoa tied in, the computer now knows airspeed and angle of attack. tie that into the stick shaker and if so equipped the auto throttle computer and or autopilot and you can give the stall warning auto throttle will advance power and the autopilot can bring the nose down. if your in a high speed stall the ground prox should have been warning of sink rate befor you ever got near a stall.
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There is a lot of good info on that site but there is also some gross error in the section on stability and control. The author is in clear and direct opposition with NASA, the FAA, Jeppesen, Embry-Riddle Aeronautical University, flight test engineers at Cessna Aircraft Corp., every aerodynamics and design text I have ever read, every pilot training text I have ever read, and every aeronautical engineer I have ever spoken with about the subject of tail down-force, stability and control. This list is not exhaustive. If anyone wants specifics, I can provide them. I am an airline transport certificated pilot with several thousand hours.

The author has been evasive and rude in response to my questioning, and has steadfastly refused to provide ANY additional supporting evidence for his "theory" that the tail of a Cessna 172 (and by implication most aircraft), lifts positively when loaded toward the aft end of the CG range. This may seem unimportant to the uninitiated but it has profound implications when trying to understand stability and control, and ignores the negative stability contribution of the wing itself versus the positive stability contribution of the horizontal tail, i.e. overall pitch stability.

The author also recommends pouring water on a frosty wing to melt the frost, and maybe he has gotten away with it, but this is lunacy. There is a possibility that water in the control surface hinges will freeze after takeoff, making flight difficult to say the least, and possibly damaging the wings and/or ailerons when they are inevitably forced by a panicky pilot, IF they break free. This is ridiculously irresponsible and dangerous advice, and I would have been fired instantly had I been caught doing that while flying professionally. Even airplanes that have been de-iced with approved fluids risk re-freezing under some conditions given enough time.

Better to stick to NASA's web site on basic aerodynamics, or books from reputable authors.

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