When NASA still was NACA, this concept for a prop driven aircraft was drawn, where
air and fuel would be ducted through hollow prop blades and ignited in combustion
chambers at the prop tips. The mixture would have been compressed by the centrifugal
forces and it was thought to be more economical, than conventional engines.
A tractor design was drawn, too, where air would pass through the hollow hub.
To me, the idea seems to be too similar to tip jet driven helicopters, which mostly
weren't economical at all, but maybe the higher number of revolutions, compared to a
rotor, would have done the trick ?
(from Aviation February 1946)
