I think I know the answer to this already.

But are wind tunnels any use to modellers ? Or is the data we'd get from them invalid for some reason ?


Thanks,
Digsy

Selig and his friends have done some excellent work at the speeds and sizes we fly at. However a lot of extra care to ensure the results were usable had to be taken. In his report published in Soartech8 by Herk Stokely there's a whole chapter devoted to calibrating and modifying the tunnel to work with acceptablly low turbulence at "our" Reynolds numbers.

However a lot of the older NACA material is suspect unless they get down to Re's of 200K or so. Often they didn't and the results at the higher numbers can be very misleading if you wan't to use it in a slower flying model.

we used it quite succesfully in our UNI project, where we predicted the lift and cruise speeds of a model glider wing

The answer is absolutely yes - with some conditions - the tunnel and instrumentation must be designed to work together at our Rn, etc. for direct results like stall, flow separation and the like to be useful.

However think of it this way. Every scale model we have flying today from the little electric models to the biggest gasser bombers to the turbine powered F-100 is flying in the big wind tunnel of the sky and all seem to work fine. I haven't seen too many full scale airplanes that couldn't be flown as models OK. So with that in mind even data from the NACA work, which is aimed toward full scale, can be useful for trends if not absolute precise values.