The 76" Lazy Ace I have does not have a flat bottom airfoil, it is semisemetrical. The large one does have a flat bottom airfoil. One unusual characteristic of the 76" version I have is, when you go inverted, it flys level hands off with no elevator trim. The only other plane I had that did this was the 40 sized Phaeton from Balsa USA. Both a real pleasure to fly. Rod