Stall Warning audio ?

[ratc]

Could anyone tell me what is driving the Stall warning tone audio output on Trent Palmer's Freedomfox as heard in some of his videos ?

Is it a stall warning system OR output from an AOA system ?

A very useful addition that uses audio rather than visual cues is always a bonus.

Thanks in advance.

[PaulSS]

It's from the AoA unit in his EFIS. They normally start beeping about 9 knots above the Critical Angle (CA) and then progressively get faster until a constant tone at the CA. Usually you just have to calibrate them by flying along and then pitching up and down 4 or 5 times (to 5 degrees nose up and nose down) and then stalling. The computer works out the pressures from the pitot and the AoA 'input' at the various speeds (fast and slow) and then just draws a line between the two to work out where the colours (green, amber, red) and the tones are displayed.

[Smiffy]

Thank you, I wanted to know that as well!

I had thought about building a free standing audble air speed indicator that works on a similar principle, to reduce the need to look at the ASI on short final. Anybody know what pressure differential is seen across pitot and static at various speeds?

[David47]

The FAA has some very good chapters in their handbook of aeronautical knowledge on this, specifically chapter 8.

[PaulSS]

Anybody know what pressure differential is seen across pitot and static at various speeds?

The differential between pitot and static pressure is going to be dynamic pressure (i.e what the ASI is displaying to you in the form of speed), so the differential pressure will be 1/2 R V2

R = Rhoe (density)
V2 = velocity suqared