Facing aileron leading edges with fiberglass


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Aileron flutter can be a problem for full span ailerons on a DLG model at high launch speeds. It is especially true when launching a ballasted DLG model in strong winds, when the outer wing panel reaches speeds well in excess of 100 mph. Aileron flutter exibits itself as high frequency oscillations of the outer aileron which can be heard as a low pitch buzz right after releasing the model. If left uncured, this problem may cause premature servo failure. Even if no damage is imparted to the model or the servos, flutter reduces your launch altitude considerably.

The two main reasons for aileron flutter are 1) slop in the control system (gear lash, pushrod slop), and 2) insufficient aileron torsional stiffness. Make sure that your control system is as tight as possible before you start reinforcing the ailerons. Remove all slop from the servo and control horn holes by applying CA to the hole and then breaking the pushrod free again. You can't do much about servo gear lash short of replacing the servo with a better one, so you will have to live with that. If tightening the control system did not help, the only solution is facing the aileron leading edges with fiberglass. This creates a shear web between the skins of the aileron and inreases its torsional stiffness by over 50% which practically eliminates the possibility of aileron flutter.

Start by preparing a strip of fiberglass slightly wider than the the thickness of the aileron. The strip must be cut at 45 degrees to the fibers. Use a sharp X-acto knife and metal straight edge to cut the strip. Be careful when handling the strip as it is very easy to deform it by stretching and nearly impossible to return it back to the original shape. Use a tight weave fiberglass with 2oz/sq.yd. weight.
Position the wing panel on the table so that the aileron is hanging off the edge and is deflected down. Lay the strip on the wing along the hinge line. Start at one end of the aileron and lay the strip onto the surface of the foam on the aileron's leading edge.
Do not try to lay the entire strip onto the LE. Do it only a couple of inches at a time. The strip does not have to be as long as the aileron. You can use short pieces and butt them together as you apply glue (see next step).
Start from the end of the aileron and apply foam safe CA glue to the fiberglass strip. Be careful to apply just enough glue to wet out the fiberglass. Do not let the glue flow onto the hinge line. This will immediately result in a stiff hinge and will require a lot of effort to return the hinge back to the flexible state.
As you wet out the first portion of the strip, continue laying it down onto the foam and applying foam safe CA glue until you get to the tip.
The reinforcement strip does not have to go all the way to the wing tip. You can stop about 2-4 inches short of the tip.
Once the entire strip is glued down, and the glue is completely set, use a piece of sanding paper to "cut" off the excess fiberglass. Press on the edge of the aileron and move the sandpaper along the hinge line until the excess fiberglass falls off.
Continue sanding the edge until you remove all of the excess fiberglass. Using sandpaper instead of a knife or a rasor blade automatically ensures that the reinforcement strip will not stick out above the wing surface, and allows you to remove all glue bumps as you go.
The final result is a much stiffer aileron, and no flutter. Repeat the procedure with the opposite wing to be sure that both wings have equal aileron stiffness. It is easier to do the described procedure before assembling the wing, but it can also be done successfully on a finished wing. If you have flown your DLG for a while and your launching technique improved to the point that you are experiencing flutter, it is time to take your wing back to the building table, remove the servos and pushrods if possible, and reinforce the ailerons with fiberglass.