In a tailless airplane, longitudinal stability is ensured by keeping the CG ahead of the center of lift and reflexing the trailing edge of the wing — that is, curving or deflecting it upward — to produce a balancing nose-up force. Differential elevons provide pitch and roll control. The pilot evidently hoped to increase that nose-up force by adding tabs to the outboard trailing edges. The trailing edge sweeps forward just as much as the leading edge sweeps back, however, and the tips, with their short chord, contribute little to the total lift in the first place, so the tabs cannot have been very effective. The T-tail, set at an angle of negative-20 degrees to the chord line, would have had more leverage, but the accident report says nothing about its size.