I am surprised this is still going. Without the turbines the engine would just be a venturi, symmetrical (as far as the air can tell) front and back. Light it up on the ground and which way will the hot exhaust go ? Both ways ie bonfire with no thrust. Add an 'exhaust' turbine and the obstruction will encourage the exhaust to go the other way, ie out of the front. Need to create a preferred route, preferably backwards.