This invention pertains to a composite turbo-fan and turbo-shaft engine which is capable of operating in
either a thrust generating mode or a shaft horsepower mode or combinations of both output modes. An engine
which is convertible between thrust and shaft horse power modes may be used to power the rotor of a rotary wing aircraft during liftoff; then, once the craft is airborne, gradually may be switched to its thrust mode for forward ?ight. Also, in turbo-fan powered multi engined aircraft, which make use of powered lift concepts, a selective redistribution of shaft power to the fans of such engines on opposite sides of the wing maybe used to effect roll control of the aircraft at low fight speeds when conventional aerodynamic control surfaces may be ineffective.