I am building a 4*40 and put dual aileron servos. For the hardware posts I am going to use Dubro HD horns. What size if any hardpoint do I need to use for these.

The ailerons are plank balsa. Before you cover, install the horns, remove them and then use CA to harden the holes. Just what I do.

John

On a plane of this size there should not be enough force exerted on the ailerons to warrant installing hard points. I too would simply harden the mount area with thin CA. Prior to applying the CA, poke a bunch of tiny holes with a T-pin in the surface directly under the horn to allow the CA to penetrate better. Sand after to smooth the surface prior to covering. Those are some pretty heavy duty horns to use on the ailerons, I would use a lighter standard nylon horn with the back plates.

Pilgrim