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VTOL/STOL Mode
The description below is our design of a commuter aircraft that is capable of horizontal flight while able to take off and land vertically.
The aircraft has twin fuselages that provide it with unique facilities. Distributing the load between two fuselages begets several advantages; these I have mentioned in the description following. I call the aircraft “Utterfly”.
The design can be adapted to a 40-passenger commuter aircraft, or for military applications as an air-assault aircraft or a gunship or an aerial re-fueling tanker among other applications
Utterfly Aerial
Utterfly Aerial
Aircraft Mode
The distinguishing characteristic of Utterfly is the two fuselages. Engines/propellers centered between two fuselages is what is innovative about this design. This single feature overcomes many weaknesses of previous designs. One thrust axis is preferable over two; wing lift over rotor lift. Passengers/cargo would occupy the two fuselages, with the weights balanced between the two.
The aircraft has wings on either side of each fuselage, with struts connecting the two fuselages. Separate struts run between wingtips. A pair of engines is mounted on a pyramid structure whose base attaches to the struts. The pyramid structure provides torsional rigidity to the pair of fuselages.
The fuselages are designed to locate the center of gravity vertically below the engines. I will discuss later why this makes Utterfly intrinsically stable. Two turboprop engines, one above the other, swivel on a shaft. Both engines are connected to a common gearbox. The gearbox drives a pair of coaxial contra-rotating prop/rotors using power from either or both engines.
The arrangement is desirable for redundancy. For horizontal flight the engines/propellers are aligned horizontally. The pair of propellers has opposite pitch; they also spin in opposite directions. Opposite pitch ensures airflow from front to rear. Opposite torques cancel gyroscope effects.
While in this mode Utterfly, takes off, flies and lands like a conventional aircraft. Its cruising speed is limited by the speed of turbo-prop powered aircraft - about 400 knots. It is in this configuration that it would spend most of its flying time.
While in hover mode the propellers act as rotors in a helicopter. Independent swash plates control each rotor. The rotor pitch is controlled as in a helicopter to stabilize the aircraft against roll/pitch/yaw instability and compensate against wind-induced drift.