Posted for "terrence o'neill" <troneill@charter.net>:

Robert,

Sounds likie an excellent system.
You say the 'danger zone' varies with flaps up and down. can you quantify
how much -- in angle of attack, or airspeed?

Terrence
L235/320 N211AL


[The instrument is calibrated for both the flaps up and flaps down flight regimes.  In both cases the aural stall warning triggers when the AOA is 15% above the actual stall speed.   Since the critical angle of attack is fixed (typically somewhere around 15-16 degrees AOA) the stall warning will occur at different airspeeds depending on the wing loading.  Let's assume that flying flaps up and lightly loaded in straight & level flight the airplane stalls at 60kias... the warning comes on at 69kias.  Same flight regime but flying at full gross weight the airplane will stall at 80kias, so the stall warning comes on at 92kias.  Same flight regime but lets do a 60 degree steep banked turn... wing loading doubles so the stall speed is now up to 120kias, you'll get a stall warning at 138kias.  When you lower the flaps the instrument senses it via a simple microswitch at the flap actuator and it switches to its flaps-down database, because the airplane technically has a different airfoil now and the stall speeds will be lower than they were with flaps up.  This calibration for the new airfoil still senses the new airfoil's critical AOA at around 15-16 degrees, but now when you're lightly loaded and flying straight and level the stall speed might be 50kias, so, once again the stall warning occurs at 15% above the stall, or at 57.5kias.  Increase the wing loading either by weight or maneuvering and the stall speeds and aural warnings both go up as required.  One might suggest that since the flaps are infinitely variable from full up to full down that the number of possible airfoils between full up and full down are also infinitely variable, and that there are an infinite number of possible stalling airspeeds associated with all those varying flap positions and one would be correct.  However, the instrument''s black box doesn't have an infinite amount of storage, nor is it necessary to calibrate the AOA curves for all those possible airfoils.  Years of testing showed that once the flaps are lowered beyond about 10 degrees the stall speeds really don't vary that much, so a simple sensor that determines when the flaps have been lowered is all that is required.  The single flaps down AOA curve will actually be within a knot or two of actual stall speeds throughout the majority of the flaps' possible locations.  Since this thread is about gear warning, though, the instrument's gear warning is strictly airspeed related, regardless of flap position, so if you set it to come on at 110kias that's where it comes on. The gear warning doesn't actually arm itself until after takeoff and you accelerate through the gear warning speed.  At that point it is armed and as soon as you decelerate through that speed the gear warning comes on.   I hope that answers your questions.  If not and you have more, bring 'em on.  <Marv>  ]