For speed you should probably use a Pitot tube which is what most commercial
aircraft use. (http://www.grc.nasa.gov/WWW/K-12/airplane/pitot.html)

If you couple that with an altimeter (from an absolute pressure sensor) it
shouldn't be too hard to detect stall... probably not as easy as one of the
other suggested methods of measuring lift directly, but I=B4m certain speed
and altitude are generally much more useful.

On 5/14/06, Zik Saleeba <zik@zikzak.net> wrote:
>
> I'm making an autonomous navigation device for an electric powered
> glider. This is the kind of plane which is normally used with radio
> control - it's hand-launched and has a 2m wingspan. In my "robot
> plane" application the plane will be controlled by some PICs and a
> gumstix SBC. It has accelerometers, gyros, GPS etc. to help it stay on
> track.
>
> One thing I haven't catered for yet is air speed. I'd like it to be
> smart enough to stay out of trouble yet having no concept of wind
> speed it could easily get into a stall without knowing until it was
> too late.
>
> I was wondering if anyone had any ideas for either stall indicators or
> wind speed / direction indicators which would be suitable for a plane
> of this size? That means small and light - it has to be able to be
> carried by the plane along with the rest of the gear I'm putting in
> there.
>
> My only idea so far is to mount a resistor/thermistor combo above the
> leading edge of the wing. The idea is that the heat of the resistor is
> normally drawn away by the air moving over the wing but if the angle
> of attack gets too great the airflow slows and the thermistor starts
> getting hotter. A second thermistor would probably be required for
> reference. I'm not entirely happy with this solution since power is a
> consideration and I don't like burning it off in a resistor. And I'm
> not sure it'd work.
>
> Does anyone have any better ideas?
>
> Cheers,
> Zik
>
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