S-POU! 2.4 by Stevens AeroModel

[fhhuber]

Well... not the ultimate. I've seen deeper under-chamber.

The deeper the under-chamber (to about 30% height to chord ratio) the better the wing is for slow flight.
Note the effective under-chamber of a 747 with the flaps and slats hanging for its version of "short field" landing. (slow is relative...)

[JetPlaneFlyer]

Originally Posted by fhhuber

The deeper the under-chamber (to about 30% height to chord ratio) the better the wing is for slow flight.

Doesn't really work that way at smaller scale, which includes most RC models but especially the smaller and slower stuff. The problem is Reynolds Number. At the low Reynolds Number that most models operate at the air wont 'stick' to the top of a very highly cambered surface. The flow separates and you get loss of lift and lots of drag (a partial stall).

For the really small and slow stuff about 4% is the most camber that works effectively, any more just increases drag. That's why you don't see very much camber on very slow flying indoor duration models, like in the pic below.

[Bill G]

Originally Posted by JetPlaneFlyer

Doesn't really work that way at smaller scale, which includes most RC models but especially the smaller and slower stuff. The problem is Reynolds Number. At the low Reynolds Number that most models operate at the air wont 'stick' to the top of a very highly cambered surface. The flow separates and you get loss of lift and lots of drag (a partial stall).

For the really small and slow stuff about 4% is the most camber that works effectively, any more just increases drag. That's why you don't see very much camber on very slow flying indoor duration models, like in the pic below.

That's my understanding. The late Jeff Raskin experimented with small model airfoils to determine efficient thin plate section for small models. I believe 4% camber produced the best results with the indoor flyer he was experimenting with. At very low REs the flat plate become the most efficient, with the trend being that the most efficient camber angle increases with RE until the point where conventional airfoils eventually become more efficient than undercamber sections.

For something a little more attractive than a thin plate, I was impressed with the results of the BSD Micro section on two 22" twin 30mm EDFs. I believe he had done a good bit of experimenting to develop the section.