Re: 2015 Wright Stuff plane

From: <bjt4888_at_yahoo.com>
Date: 15 Nov 2014 15:01:06 -0800

The red band, believe it or not, is a 1.2 gram lump of clay needed to locate the CG at 3.375" behind the wing trailing edge. That particular model is the 7 cm wing chord "State" rules version and the neutral point (using the Bernie Hunt spreadsheet) is 3.75" behind the wing trailing edge. You'll notice in the picture that the clay lump is very near the CG for the other two airplanes. The starting CG that our team selected for the 8 cm wing is 2.5" from the wing TE (ssm around 13%). The kit designer actually recommends an even smaller ssm, which requires a 2.75" behind the wing TE. Flight stability is fine with the small wing tiplets. As the wood supplied with the kit for the wing LE and TE is good, but not super-good, the wing bends into a slight tip-to-tip curve of about 1/4", or maybe a little more, giving the wing a small amount of dihedral effect that appears to help the roll stability. The kit propeller surprised me a little. Although the prop blades are rather smaller than other successful SO designs from past years, with a longer, thinner motor (18" of .055g/in) it performs pretty well. Of course, I've guided the students to think in terms of testing a larger blade area flaring prop or a bucket prop to see if duration can be improved.

 Brian T.
Received on Sat Nov 15 2014 - 15:01:06 CET