I am thinking about building a larger airplane to use my MOKI 215cc radial gas engine. I have a Pegasus glider tug with a 115" wing span, and over-powered by a 3W-157B2 engine. I'd like to build something a bit larger for the radial, and not sure what airfoil to use. My Pegasus uses a G30U218 foil which is semisymetrical and works OK for the purpose. I'm looking for something similar to a giant trainer, and wondering what would happen if I increased the size of the Pegasus a few percent, and changed the airfoil to a flat bottomed foil similar to that used on normal 40-sized trainers. Thoughts?

Larry Fitch

Hi Larry -

I have a 1:3 Frisch Wilga with a DA150 which had a 15% flat bottom airfoil. It flies like a big trainer. One of our other tow pilots uses a Hemple 38% Super Decathlon with a non-flat bottom airfoil and also powered with a DA150. Very nice plane and certainly aerobatic, but in many respects when it just comes down to towing and landing they are more similar than different.

You would expect the flat bottom wing to be more floaty, but during the tow it really isn't a big factor. Proper landing flaps solves the floating issue for landings. I think the other design parameters such as wing area and tail volume will have much more of an impact than the choice of a flat bottom or semi-symmetrical airfoil (with reason).

The Moki has a nice wow factor, but be aware that it will be inferior to the 150. It weighs more and has less power.

Ken Kaye

use an HQ 3.5/15

tastes great and less filling!!

The NACA 2415 is a standard semi-symmetrical lifting airfoil.
Shouldn't fly too fast, but would have better behavior than a flat bottom wing.

The NACA 2415 is a standard semi-symmetrical lifting airfoil.
Shouldn't fly too fast, but would have better behavior than a flat bottom wing.