I am building a DH Gypsy Moth biplane from an old kit and am wondering how much travel up and down I should allow. The aileron is 2" x 14" and is hinged nearer the top of the wing/aileron joint as per drawing. The thickness there is 7/8" and I have sanded off some of the lower portion to allow more than the 5/16 or so that was available. How much more should I have? Doc

5/16" for a 2" wide aileron is just about 9 degrees of travel. For my biplanes, I use about 12 degrees. However, if your aileron is top hinged, it sounds like you should have no trouble getting all the up travel that your linkage is capable of providing and that your problem is getting enough down aileron. For down aileron, 9 deg is probably fine. Most bi-planes need ailerons differential where the up aileron travels more than the down aileron does. 12 deg up and 9 deg down is probably about right.

Thanks! I might be there with the sanding I did. I'll reassemble it this morning and check it.

After more sanding I achieved your recommended 9 degrees of travel. If more is needed I'll have to remove mat'l from the wing.
Thanks again for your help! Doc