Alas, another airfoil quest

[roger111]

I have flown full scale aircraft most of my life and know standard airfoils. However, I am flying a ParkZone Aero Challenger and after transmitter problems caused a few high alt nose dives into the ground, things are not exactly in line now that I have repaired the tail boom! The wing is undercambered. Where do I measure the angle of attack as compared to the flat V tail? I am guessing it would be on a line from the tip of the leading edge where it stops curving down straight to the trailing edge. Is this incorrect? If I set the angle of the flat tail the same as the angle of the line straight across the bottom, front to back, of the wing would I be setting the starting points correctly? Sorry if I seem to be repeating myself. I am just trying to be clear what I am asking.

Thanks for any help

Roger Breckenridge

[Dave Robelen]

Hi Roger,
In general you are correct about the airfoil being measured from the center of the LE to the TE. This is the method used by the theoretical folks when presenting data. As far as the setup for an undercambered airfoil, I would definitely start with some positive incidence. These airfoils have a pretty strong nose down pitching moment, and there would be a good chance the model would tuck it's nose and not recover.
My personal method is to add incidence (or decalage) until the model almost stalls from a brisk hand glide. I then back off a bit and start powered flights.
I hope this helps, Dave

[roger111]

Thanks Dave. I found my new wing to be warped causing several uncontrolable crash's and put my old wing back on. I have been gun shy to try again without knowing where to set things.