For Valin Thorn -

Actually, a stall warning device IS required for certified airplanes.  Here's the excerpt for FAR Part 23...

Sec. 23.207  Stall warning.

(a) There must be a clear and distinctive stall warning, with the flaps and
landing gear in any normal position, in straight and turning flight.
(b) The stall warning may be furnished either through the inherent
aerodynamic qualities of the airplane or by a device that will give clearly
distinguishable indications under expected conditions of flight. However, a
visual stall warning device that requires the attention of the crew within
the cockpit is not acceptable by itself.

I'll note that this is different from an angle-of-attack display, although Jim Frantz' system with it's auditory signal ("angle ... angle ... PUSH") meets and exceeds the requirements of this section.  I'd hope that if he gets it TSO'd then the certified companies will start replacing those cheesy stall horns.

So, yeah, stall warning IS required but an AOA readout is not.

- Rob Wolf
360Mk2, 50%, with AoA system half-installed already...