During the final phase of World War II, a plane was desperately needed which could defend Germany against constant Allied bombing raids. The plane that was developed for this task was the Focke-Wulf Triebflügeljäger. This inceptor, its name directly translated from German as “Thrust-win Hunter” was a project masterminded by Professor Otto Pabst. The designed was revealed in the third quarter of 1944
This VTOL or Vertical Take-Off and Landing tailsitter interceptor was used in areas where there were no airfields, and utilized only small clearing for takeoff or landing. It could be rapidly deployed, and had an armament able to deal with fighters, and outgun many bombers.
This strange little craft did not have any wings but was lifted into the air using a rotor or propeller unit that was located a bit below the halfway mark, between the tail and the cockpit of the plane. Sitting on its tail, nose pointed skywards, the giant propeller would lift it off the ground, with the tail controlling the transition to horizontal flight.
Assembled as a three blade unit, the propeller was joined to the body in such a way that the whole unit rotated around the aircraft. Ramjets at each blade tip was used to power the blades, with simple rockets bringing the blades up the operating speeds required by to utilize the ramjets. Fuel was stored within the wings/blades and then piped to the ramjet engines.
By altering the blade pitch, the pilot was able to change both the speed and thrust being delivered to the plane. Directional changes could be accomplished by altering the ailerons, serving as both elevators and rudders, on the four tailplanes. The tailplanes were also used to counteract the tendency of the aircraft to start spinning in the rotational direction due to uneven friction created by the blades circling the fuselage.
Wing tunnel test confirmed the feasibility of this aircraft and gave the Germans the final verification needed for taking this plane to production.
The Triebflügel was to be armed with two 30 mm MK-103 guns, and two 20 mm MG-151 guns.
The cannons in the forward fuselage had to be angled slightly downward when looking at the centre line of the fuselage because when the craft was in forward flight, it needed to have a bit of a pitch with its nose up to provide upward lift along with mostly forward thrust.
This procedure could be achieved with little effort. Designed to be able to react quickly to threats, this aircraft could be readied for takeoff by simple moving it to an open space and starting up the rockets, bringing the ramjets up to speed. Due to the spinning rotor, any movement in and out of the aircraft was not feasible once the rockets were stated.
This dangerous maneuver would have the pilot slow down the aircraft to a point where the plane could transition it from horizontal into vertical flight. When this was achieved successfully, the pilot could reduce the power to let the craft descend to a point where the landing gear made contact with the landing area. Only one large sprung wheel that was located at the very end of the fuselage made up the undercarriage on which to land the plane. To allow the craft to be moved and to steady once it on the ground, four small un-driven wheels were placed on each tailplane on extendable struts.
This complicated maneuver would have the pilot fly blindly, or at least land blindly, since essentially he would be landing in reverse, facing away from the area he would be landing on. The spinning blades also impaired vision of the ground and unlike other prototype post world war two designs this had a fix seat position for the pilot. As with takeoff, the pilot also had to remain inside the aircraft while the rotors were spinning down. Fortunately, rotational speed was low but the weight of the ramjets and fuels caused the propeller to have a high inertia.
This plane, only having space for the pilot, had a length of 30 feet. It had a wingspan of just over 36 feet with a weight of 5,512 pounds. It was powered by 3 Pabst ramjets that was capable 8.9 kN or 2,000 lb thrust each. It also had 3 Walter liquid fuel rockets and 2 German Walter 109-501 RATO units that were capable of 14.71 kN or 3,306 lb thrust each.
It had a calculated maximum speed 540 knots with a designed limited never exceed speeds in excess of 1,458 knots. Its minimum control speed was 230 kilometers or 143 miles (124 kn) per hour. It was to have a service ceiling of about 15,300 m or 50,197 feet and a rate of 50 meters per second or 9,800 feet per minute.
No complete prototype had ever been built as the Triebflügel had only reached wind-tunnel testing when the Allied forces reached the production facilities. While the plane never reached production, the Triebflügel’s influence can be seen in American prototypes such as the Lockheed XFV and the Convair XFY Pogo.