Do you have to fly a S4083 Airfoil fast?

Regarding the S4083. You don't like it because it best cl is too low? In other words it needs to fly fast. I find that I add camber when thermaling with this foil.

From : Don Stackhouse

According to my studies, the problem with the S4083 is that its best Cl is TOO HIGH. It has a very good L/D, but at a Cl so high that it is totally unsuitable for a hand launch sailplane, and the L/D at lower Cl's is terrible. On HLG's, Reynolds number is extremely critical. If you fly a normally proportioned HLG with this airfoil at normal weights, the airspeed is so low that the Re is terrible, which gives you a lousy L/D. If you try to fly it at higher speeds the L/D is lousy because you're at a too low Cl. If you ballast it up so that it flies at a high Cl at a normal speed and Re, the weight is so high you can't throw it. If you reduce area by increasing aspect ratio to get the wing loading and airspeed up, the Re goes way down and the L/D is lousy. If you reduce area by reducing span to get the wing loading up, the induced drag goes up and the L/D is lousy.

In any case, no matter what you do, the airfoil has a very narrow performance band, so a model using it is essentially a one-speed aircraft. Goodbye to any chance to launch and penetrate while still being able to thermal! By the way, the reports I've heard from the field regarding the in-service performance of this airfoil have been in agreement with these conclusions.

On the other hand, I think a modified S4083 might do very well in one-speed aircraft, such as the SAE weight-lifting competition, or on powered indoor R/C models. In fact, I have the ribs cut out for one of those now, using a very modified S4083 (of course, I guess that means it's not really a S4083 anymore though, is it?).

Don Stackhouse
DJ Aerotech