Orion, I've cut and pasted your last post to get this string started Dan Dan, to answer your question, you're right, fixing an aft spar would give you a stiffer wing, the question however is whether that is actually what you want. The drawback to this approach can be that you will get stresses in the wing where you may not necessarily want them. The Glasair is an excellent example. Due to their continuous structural design (one piece wing), the aft spar is configured for taking some of the bending load. For most flight this is OK, although there is a stress concetration at the aft spar in the area of the wheel well cutout. It turns out that adding material to take care of the stress concetration actualy stiffens that part of the wing and actually makes the stress case even worse. At high angles of attack however, this stress concentration becomes the highest stressed part of the wing. If we examine the Part 23 requirements for aerobatic flight and composite structures, by this definition the Glasair wing should not be considered aerobatic. The FARs require 6 Gs limit and a safety factor of 2.0 for composite structures (not 1.5). As such, the ultimate load needs to be 12 Gs. The FEA analysis I did for this condition resulted in stresses well over the failure criteria for fiberglass. This was quite a while ago but if I recall correctly, the ultimate strength of the wing at high aoa was less than 9 Gs. For most flight this is OK however, when you add in the long term effects of fatigue loading, Glasairs that are continuously used for aerobatic flight may develop weaknesses down the line. For this reason and a couple of others, I prefer to pin the aft spar and let it carry only the local loads of the ailerons and the flaps. As far as a stiffer structure is concerned, how much stiffer do you want it? You can design the skin laminate in such a way that it makes up for the lack of a fixed aft spar, and develp the same characteritics without the added complexity of loading up the aft part of your structure. But of course that's up to you - you may have different requirements or reasons than I use in my selections. A stiffer wing is good, especially considering controll crispness and flutter - all I'm saying is that there are different ways to skin a cat.