AG35, 36, 37 lift/drag polars wanted

[Sail 'n Soar]

Does anyone have the CL vs. CD polars, preferably from low turbulance tunnel measurements, for the Drela AG35, AG36, and AG37 airfoils? I am especially interested in these sections because they were designed to be compatible with "classic" D-tube forward/rib and film or fabric aft construction and to work well at RE's below 100,000. However, their relatively thin, low camber sections implies that their CL,max are relatively low.

[Ollie]

The polars for the AG35, -36, -37 and-38 can be found at the Charles River R/C web site under Articles and Tips and from there under Allegro Lite. These are X-Foil generated polars. I haven't heard of these airfoils being tested in a wind tunnel yet. I think the AG34 is not much different than the S3021.

The low maximum lift coefficient isn't much of a problem if you make the wing loading low enough. The Allegro Lite and Bubble Dancer are predicted to have minimum sinking speeds well under one foot per second! This compares quite favorably with typical two and three meter designs with sinking speeds of 1.1 feet per second and up. Since these airfoils were an integral part of the Drela wing designs, you woud be hard pressed to do better with a wing planform or twist that deviated.

[Sail 'n Soar]

Ollie,

Thanks for the source. I thought I had seen them somewhere. In terms of the low CL,max, I'm working on a powered glider with a scale-like fuselage, i.e., large cross-section and associated Cd, which pushes the desired CL at max L/D or min sink higher than the minimal fuselages do on purpose sailplanes like Allegro Lite. (I'm still into wanting my gliders to like gliders.) Haven't done the actual trades yet, but I'm hoping the polars will show these foils suit my needs nicely.

Gerry

[Sail 'n Soar]

Ollie,

Checked out the polars and the XFoil predictions look great. Being able to build something close to design by acoiding covering drag with these foils, alone, is worth going with this foil family.

Gerry

[Ollie]

By the time you prorate the fuselage coefficient of drag to the wing area, I'll wager that the (fat) fuselage drag will be under 5% of the total drag at air speeds up to and including best L/D. In computing the lift over drag, the fuselage drag term is the coefficient of fuselage drag times the fuselage wetted area divided by the wing area. Because of the fuselage length it operates at a much higher reynolds number than the wing and the coefficient of fuselage drag benefits from that higher reynolds number too.