Foam board bowing


New member
I built a tiny trainer and the horizontal stabilizer is slightly curling. The first few flights were flown in grass with as bit of dew and the bottom of the stab got wet. I think this is the reason. Aerodynamically, it isn't a problem and I don't really care if it's curved or not. The problem is that it affects the throw of the elevator. The servo has to "pop" the stab flat to pull the control surface up.

Is there a fix that can keep the stab flat? I'm resorting to holding to the tail with books on the very outside edge of the stabs and putting a weight on the tail to stretch it back, but it only works for a short while.


Flite is good
Everything that can fix it will add tail weight, so be prepared.

Make a cut in the stab from tip to tip, about midline of the tip chord. In that slot you can glue a -

BBQ skewer
Carbon tube
2mm carbon flat

Be prepared to add nose weight to achieve CG.


Master member
You can always add a bracing wire (nylon thread) to 'pull' the tail plane flat permanently. Adds virtually no weight.
After all virtually all early planes absolutely relied on bracing wires to make the wings strong enough to fly!


Master member
If it warped because it got damp, making the opposite side skin damp might warp it back but I will be surprised if it stays flat. An old fashioned steam iron on the lowest/coldest steam setting could "iron" it out flat, particularly it you let it cool down sitting on the part on a flat surface like you're doing with the books.

Scoring only the paper on the bottom in the middle of the bend, and repairing that with cellophane or thin packing tape might release the tension enough to work.

Carefully peeling the paper off the bottom then reglue-ing it back on? Or just leaving it off?