Polyhedral tip angle?

[SoaringDragon]

I'm rebuilding a Sweety 60" polyhedral thermal glider, but I don't have the original plans. I'm attaching the 11 1/4" wing tips to the 17 1/2" long wing center sections, what angle should they be relative to the center sections?

[Sparky Paul]

More than the center section.
If the c/s has 3 degrees per side, then try 6 degrees on each tip.

[Ollie]

http://members.cox.net/evdesign/pages/spiral_stability_gyro.html

"Models with substantial dihedral such as rudder and elevator sailplanes counter this effect by their tendency to yaw outboard in circular flight. This yaw in combination with the dihedral increases the angle of attack of the inboard wing relative to the outboard wing, countering the effect of the speed variation over the wing. By tuning the wing dihedral and vertical tail moment arm, any degree of spiral stability can be achieved. More dihedral and longer tail moment arms give more spiral stability. Neutral spiral stability can be achieved by setting:

(EDA) x (Lv / b) / (Cl) = 5.0 approximately.

Where:

EDA = equivalent V-dihedral angle in degrees, each wing
Lv = vertical tail moment arm (from wing MAC/4 to vertical stabilizer MAC/4)
MAC/4 = quarter chord point of the mean aerodynamic chord
b = wingspan
Cl = lift coefficient while circling (a good guess is 0.6 to 0.9 depending on camber)

Note: Lv and b must be in the same units (inches or cm or whatever)"

[SoaringDragon]

Ok, well it looks to me like a lot more than 6 degrees...I've gone by looks (before you guys posted) and it looks like over 15 degrees to me. I test flew it today, and it seems fine, though I have to work on my TX before I can do a proper test. (bad connection in the battery pack, it killed my Hyperwing)

[SoaringDragon]

Ollie, thanks for the formula...I'm assuming the rudder counts as part of the vertical stab's chord, correct?

[Ollie]

Yes, vertical tail total (fin and rudder) area. I quoted the whole idea from Blaine K. Beron-Rawdon.