Many of the planes I try making for the Indy Air Race tournament tend to crash into the ground. I think I know one of the reasons, but I don't know how to solve it.
Presumably, when your plane is flying side ways it will only have its vertical stabilizers providing lift. Since these are usually only located on the rear of the plane this results in only the rear having lift, pushing the rear away and the nose to the ground. This seems a undesirable, especially considering that the AI doesn't use yaw.
I think if this effect could be stopped or reversed, than it might prevent quite some crashes. Unfortunately, placing the vertical stabilizer on the front doesn't work. So if anyone thinks I'm wrong, has ideas for a solution or just feels like chatting, please drop a comment.
You have to improve the stability of the longitudinal axis.
Dihedrals are key here. They help keep the lift force parallel to the direction of gravity more constant through the roll up to a certain point.
Another thing to do is engineer your plane so that the AI can handle flying it inverted. One trick to test this is removing the cockpit, flipping the entire plane on its back, then replacing the cockpit on the plane's belly, and adjusting all the control surfaces. If the AI can handle flying it, you did good.
@UnknownNate I actually tried that, not only did I lose a lot of vertical stability, it also barely reduced the downward drift...