flap hinge structure questions

[Karl B²]

I'm building a lightweight motor glider that will incorporate a one-piece balsa built-up flap along the non-dihedral center section. It's roughly 20% chord.

The LE & TE of the flap will use 1/32" balsa, and the aft wing will incorporate a spar (not shown) of 1/8" sq. balsa top and bottom w/vertical 1/32" shear web just forward of the separation. The grid is 1/2" squares.

With the curved sheet flap LE, I expect it should be rigid enough to span 30" with hinges at each end and one in the middle, if the flap LE is unbroken.

Semi-unorganized questions:
1) Would hinge supports below the wing work? Extended rib hinges would be simpler but the flap LE would be broken, concentrating torsional stress at each hinge point. Bottom hinge supports would cause difficulty in covering the open framework.

2) would a slotted flap make more sense given that to make it so would not be that much more complex?

3) Any need for a spar in the flap? Besides the longitudinal sheeting at LE & TE, each rib will have 1/32" chordwise rib caps.

If anyone has any suggestions or pictures, they would be appreciated. I've only done plain beveled flaps to date, and I'm willing to add considerable complexity in exchange for low drag and light weight this time.

Thanks,
Karl

[Sparky Paul]

I'd use a wire hinge at each end, fitted into an aluminym tube glued into a 1/4" sq. strip.
The tube is at the center of the radius of the flap leading edge.
The wire would be sewed to a ply semi-rib in the wing proper.

[Karl B²]

Would you run the hinge wire and tube block full length, or just at the ends?

With the wing flexing up at the ends from flight loads and the middle of the flap flexing up (and back) when extended, I think I'd still need a hinge of sorts at the center where control linkage will attach.

[Mike James]

Here's a set of pages I built last year, illustrating a variety of ways to do flaps, slats, and spolers. http://homepage.mac.com/mikejames/rcu_flaps_site/index.html