Clearly any exhaust from an APU, if pointing in the correct direction, must contribute something in the way of thrust. Without wishing to detour too far from the original thread, the Shorts Tucano provides 1151 hp. 1100 hp drives the prop/gearbox, and the equivalent of 51hp comes out of the exhaust eductors as thrust. I know you also get thrust out of a helicopters jet exhaust. Don't know how this engine size compares with an APU in a big jet, but wouldn't have thought they would be much smaller