Changing Dihedral?

[raddivr]

I posted this in "sport models (glow)" before realizing this one was here.

Hey all,
Im fairly new to the hobby. I just solo'ed this last weekend.
Im in the process of building another wing for my Great Planes PT-40. The original wing has 8" of dihedral. This is their recommendation for the "trainer" wing. I want to build the the next wing with less. They say the Sport wing has 6". but i think id like to go less for easier loops and rolls and such. (ever tried doing an inverted loop with 8" of dihedral?) Anywho, has anyone ever modified their birds with less than what the plans recommend? what are the pitfalls that can be seen by doing this.

Id love to get your opinions on this.

Thanks.

-Rich

[Dave Robelen]

Hi Rich,
You did not say, and I cannot remember if the version you are talking about has ailerons. Assuming it does, the lower the better on the dihedral. Even 1" under the tips would be more than enough. A high wing airplane has "effective dihedral" because of the wing being above the CG. You would have to droop the tips several inches to get down to zero dihedral effect.
If, by chance you are flying 3-channel, than you would want to keep the 6" reccomended. As the dihedral comes down, so does the roll response to the rudder. A good thing with the aileron setup, but it could get nasty in wind gusts if you were depending on the rudder for recovery.
Regards, Dave

[raddivr]

Dave,
Indeed i forgot to mention it had ailerons. See i am a newbie. :)
So theoretically i should be O.K. building a straight wing? This would be much easier to do because i wouldnt have to custom shape the center joiners.
should i keep the recommended 3 degrees of washout?

Thanks for the help and the earlier explaination.

-Rich

[Dave Robelen]

Hi,
A straight wing will work fine. The only reason people object to them is that they look "droopie". With a rectangular wing equipped with ailerons, I would leave the washout out. I doubt if it is doing all that much anyhow, and it is easier to build a flat wing.
Regards, Dave