Guillow airfoils

[svaughn]

Hi,

I've recently worked on 900 and 500 series kits and am curious about how Guillows selected the airfoil. I know this decision was probably made way back in the 50's (maybe earlier), but maybe someone from Guillows knows.

The foils are odd to me because the highest point of the profile is so far back. Maybe it is all about making the wings easier to build. I'm pretty sure they are not scale and they don't look like low-speed airfoils I have seen.

Also, has anyone experimented with a different airfoil profile on any of the Guillows model kits?

Steve

[wingnut]

First I can say these airfoils definitely aren't scale because they are flat bottom airfoils, which none of the 900/500 series full scale aircraft had (although the bird-dog might be close). As far as why they were selected (I'm guessing here) the flat bottom makes them very easy to build when compared to other airfoil shapes because no jigs or other equipment is needed to assemble them.
The observation you made about maximum thickness being so far back is possibly due to the fact that these wings were modified to move the center of pressure farther back along the wing so they require less nose weight for stable flight? When the other parameters are set ( tail moment, wing area, tail area, etc) because you're designing a replica, you have to fiddle with the airfoil to get the stability you need for flying.