Yes, I agree, trimming a bipe is not just about stability.
Back to the original question, during the 20s/30s, according to an old timer, it was common to rig bipes with some washout. Some of them had fairly high aspect ratio wings even though they were bipes.
It’s common to set the top wing a little negative to the bottom wing (pos. stagger). The idea is that down wash from the top wing causes the bottom wing to fly at effectively a lower angle of attack, so setting the top wing a little negative evens it out. One pretty experienced bipe flyer on this forum says that by testing he has found it works well on all his aerobatic bipes. I set up my own that way.
It’s also common to set the top wing a little positive to the bottom (pos. stagger). The top wing stalls first and the bottom wing, further back, is still flying. I don’t do that because that’s making the lower wing do the job of the stab. I want the lower wing to carry it’s weight. It would make it hard to do snaps too.
Gordon Whitehead, who has published many scale designs, explains these theories and uses no difference between top and bottom at all, and he never mentions washout. Hard to argue with his success as a scale bipe designer. Jim
Last edited by buzzard bait; 10-02-2018 at 05:54 AM.