I'm getting ready to start building my Spectre 120. I've got a couple of questions / concerns to ask you about.
1. I'm led to believe that the aileron hinge cut made to form the aileron is made with a continous width?

IE. As you get closer to the upper skin, the 3/32nd gap of material removed doesn't narrow. Am I correct?

From : Don Stackhouse

That's correct. Think of the skin hinge on the upper surface as a very short, but very wide leaf spring. The stiffness of a leaf spring depends (among other things) on its thickness (in this case the thickness of the upper surface skin) and on the spring's length (in this case the width of the hinge slot). Both of those are constants along the span of the hinge.

The thickness of the foam removed is not a factor in the stiffness of the hinge, only the width of the slot.

If you taper the slot, the stiffness of the hinge will increase in the narrowed areas, which will also increase the stresses in the upper skin when the aileron is deflected. This could result in overstressing the upper skin, which could (in extreme cases) lead to cracking of the skin.

My other item is a concern. The plans show the aileron extends to within 4 inches from the tip. This leaves a very narrow section of wing between the leading edge of the aileron and the leading edge of the wing. Is the tip strong enough???

Excellent question, and yes, it is strong enough. The carbon spars are what give the tip its strength, and those run all the way to the tip, undisturbed, ahead of the hinge slot. In addition, on the Spectre 120 we do not make a chordwise cut at the outer end of the aileron, so the aileron is still tied to the tip. Although this doesn't have much effect on the up-and-down bending strength of the tip (carbon is so much stiffer than the fiberglass skin that the added bending strength of the fiberglass skin of the aileron in that direction doesn't really add that much to the total), the lack of a chordwise cut does help reduce stress concentrations in that area, and it also does add significantly to the fore-and-aft bending strength of the tip.

Note, the tip is plenty strong enough even with a chordwise cut at the tip of the aileron, for folks who insist on doing it the conventional way. However, leaving the aileron tied at the tip improves the strength and flutter resistance of both the wingtip and the aileron, it reduces edges that can catch on stuff during landing, it reduces aerodynamic drag, and it alters the twist distribution when the ailerons are drooped in concert with the flaps for thermalling. Roll response is excellent with the tied tips at all flap deflections, provided you set up the ailerons per the instructions.

Aerodynamically, this change in washout distribution due to the tied aileron tips accomplishes much the same thing as the latest trend toward six-servo wings (i.e.: with thermalling flaps deployed, it keeps the lift distribution more smooth and elliptical than a four-servo wing with non-tied aileron tips or with trilerons can do). However, according to our analyses, the lift distribution from our four-servo Spectre 120 wing with tied aileron tips is even smoother and more elliptical than a six-servo wing with conventional ailerons, and without all the extra weight, complexity and cost of the extra servos.

Don Stackhouse
DJ Aerotech