If you want something little more complicated have a Google for lift reserve
indicators.
Requires a probe or a port on the wing. Simple differential pressure sensor
1-3 psi
into the a/d and you can have a numeric indication of how much lift you have
or how
close left to stall. Isn't affected by cg or wing configuration ie flaps up
or down
and so on.

Dave

> 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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