the umbrella is a wing in that example, forget air going to it...

heres a forgotten fact.. a porp dosen't blow the plane forwards, it pulls it forwards, a prop is a spinning wing, the "wind" is a by product. in other terms, if you mount the engine to the ground, theres no way prop wash can get around it, but it'll still pull with all its might. the difference being in flight the air is moving. on the ground its sitting in its own turbulence.

mounting the engine ON the top of the umbrella wont hurt your pulling power one little bit. might hurt it a few seconds later when it hits the deck tho LOL