RE: What makes a plane do a good elevator ????
Man, you have bit off a big one here! I'm no aerodynamics guru, but please let me give an opinion.
I think that small wingspan planes just tend to suck at 3D. It must have something to do with Reynolds Numbers. I don't know Reyonlds numbers from Reynolds wrap, but here goes.
To me, it breaks down to simply this. An air molecule is only so big. It will always be pretty much the same size no matter what. A wing, that is in a harrier, does not "fly" based on the explanation that we got from Bernoulli's principle. No lift is being created by the mysterious vacuum over the rear wing. The wing stays aloft more like a boat hull stays on top of water. Small hulls, or wings, need more speed to hold up the same weight in a stable fashion. Large planes (or boats) with relatively high wing loads (like aircraft carriers) stay stable, where small planes lightly loaded, like 40 size fun fly planes, do not.
Also, the inertia of a large plane maintains stability better than that of a smaller one, so just making it bigger will help some.
Another note is that biplane wing loads are deceiving. To compare wing loads honestly, reduce the surface area of the bipe by 40%. Meaning that a bipe with 1000 squares is fairly well compared to a monoplane with only 600 squares. The two wings do a few funny things to each other, and do not act as you might think. Verify this before you move on.
If I were convinced to create the plane you describe, I'd do this.
1) Start with the Sig Ultimate. I like the plane (and it's a good platform), but agree that the harriers and elevators rock as bad as any plane EVER.
2) Increase the overall size by 120%.
3) From that number, round up from 960 to about 1000 squares.
4) Move the top wing forward slightly. This will "activate" a little more wing area.
5) Lower the horizontal stab a bit, to help with control coupling.
6) Shoot for 6.5 to 7 pounds max. 8 pounds would fly like a brick I think.
If you build this, I gotta see it, so keep us up to date.
Are there any real aerodynamics guys that can help us out here?