Howard, I have a question or two. When you said you tried it on one side I presume you meant either the top or bottom side of the TE.
I'm sorry; what I said wasn't very clear, as I noticed when I looked at it again. I put them on the bottom of both wings. It took a lot of up elevator to fly level. That was the (negative) pitching moment.
Way back in my free flight days, I took out a well trimmed 450 sq in power ship with a flat bottom airfoil, 8" chord. I trimmed it to hand glide straight. Then I put a 1/8" square balsa strip under the trailing edge of the left wing all way out to the tip. In about a 50' long hand glide it would turn right which told me the left wing was lifting more. This was low speed lift. The Gurney lip is said to be more effective at higher speeds and higher AoA.
Now on a symmetrical airfoil wing if the Gurney lip were placed both above and below the TE would this reduce or eliminate the pitching moment? And then would there me any increase in lift or drag? Your thoughts on further experimenting would be appreciated. Regards, SLEEPY
The free flight case would have been high angle of attack if it was a normal glide speed.
For a symmetrical airfoil with symmetrical Gurney flaps, I'd think that the pitching moment would be the same as without, and maybe lift and drag would be the same, too. Give it a try.
I can think of two things that would be fun to do. First is to build a wing with the airfoil faired into the two-sided Gurney flaps: namely, an airfoil that's whacked off at the TE when it's still 1/4" thick or so. Gary James suggested this awhile back. It might work as well or better than a wing that comes to a point at the TE, for our size airplanes, anyhow.
Another thing to try would be a Gurney flap that moves up and down, connected to the elevator like regular stunt flaps. The mechanism would be a little weird, but it would give some flap without hinge moment.
Topic: Gurney lip (Read 1207 times)
