It seems as if the participants in this thread assigned little if any significance to the fact that you reported this is a SPAD.

SPADS have NO aileron gap. There are no hinges to come loose.
They can have sloppy linkages.

Flutter is caused by sloppy linkages or flex. Aileron gap itself is not so bad, but it is a place where the ailerons can flex because of aerodynamic loads. That's why sealing the gap helps: it stiffens the mechanism. SPADS don't have aileron gap, but they DO have is very flexible ailerons. And the mounting for the control horns is usually not very rigid in normal SPAD practice. Grab the tips of your ailerons and push them up and down. See what I mean?

Somebody mentioned balancing. Balancing doesn't stiffen the mechanism, it just changes the phase relationship of the flutter so it tends to be self-cancelling. However, going to the trouble of balancing the control surfaces on a SPAD is a little like the proverbial polishing of a tu... -er, you know.


I had a SPAD once that fluttered. It looked scary, but it did not hurt anything. SPADtanium (coroplast) is pretty hard to hurt that way.

The dual servos are overkill but should stiffen things up a lot. If it still flutters, taper the ailerons outboard of the servo. If they are 1 1/2" wide, taper to 3/4" and see if that helps.
Be sure the mounting for the control horns is stiff. Don't use the little setscrew thingies that go in your servo horns, especially not with the plastic retainer rings. Use Z-bends at the minimum, or (preferred) a clevis soldered to one end and an adjustable clevis on the other end of each pushrod. Just be careful that everything fits snugly.

If you'll cut one rib to fit the inside of each wingtip and glue them into place, you may find that it stiffens the wing structure a lot. 1/8 balsa would be easier to work with for this than coroplast, but whatever you choose will be fine.