Waprlanes of Germany: Luftwaffe Focke-Wulf Triebflügeljäger

Focke-Wulf Triebflügeljäger

(Luftwaffe Photo)

Focke-Wulf Triebflügeljäger, experimental project (model).

The Focke-Wulf Triebflügel, orTriebflügeljäger, literally meaning "thrust-wing hunter", was aGerman concept for an aircraft designed in 1944, during the final phase of theSecond World War, as a defence against the ever-increasing Allied bombing raidson central Germany. It was a vertical take-off and landing tailsitterinterceptor design for local defense of important factories or areas which hadsmall or no airfields.

The Triebflügel had only reached wind-tunnel testing when the Allied forcesreached the production facilities. No complete prototype was ever built.

The design was particularly unusual. It had no wings, and all lift and thrustwere provided by a rotor/propeller assembly 1/3 of the way down the side of thecraft (roughly halfway between the cockpit and tailplane). When the plane wassitting on its tail in the vertical position, the rotors would have functionedsimilarly to a helicopter. When flying horizontally, they would function morelike a giant propeller.

The three rotor blades were mounted on a ring assembly supported by bearings,allowing free rotation around the fuselage. At the end of each was a ramjet. Tostart the rotors spinning, simple rockets would have been used. As the speedincreased, the flow of air would have been sufficient for the ramjets to workand the rockets would expire. The pitch of the blades could be varied with theeffect of changing the speed and the lift produced. There was no reactiontorque to cause a counter rotation of the fuselage, since the rotor blades weredriven at their tips by the ramjets. Fuel was carried in the fuselage tanks,and was piped through the centre support ring and along the rotors to thejets.[3]

A cruciform empennage at the rear of the fuselage comprised four tailplanes,fitted with moving ailerons that would also have functioned as combined ruddersand elevators. The tailplane would have provided a means for the pilot tocontrol a tendency of the fuselage to rotate in the same direction as therotor, caused by the friction of the rotor ring, as well as controlling flightin pitch, roll and yaw.

A single large and sprung wheel in the extreme end of the fuselage provided themain undercarriage. Four small castoring wheels on extensible struts wereplaced at the end of each tailplane to steady the aircraft on the ground andallow it to be moved. The main and outrigger wheels were covered by streamlinedclamshell doors when in flight.

When taking off, the rotors would be angled to give lift in a similar manner toa helicopter. Once the aircraft had attained sufficient altitude the pilotwould tilt it over into level flight. The rotors continued spinning in levelflight, maintaining 220 rpm at the aircraft's maximum forward speed.

Forward flight required a slight nose-up pitch to provide some upward lift aswell as primarily forward thrust. Consequently, the four cannon in the forwardfuselage would have been angled slightly downward in relation to the centrelineof the fuselage.

To land, the craft had to slow its speed and pitch the fuselage until the craftwas vertical. Power could then be reduced and it would descend until thelanding gear rested on the ground. This would have been a tricky and probablydangerous maneuver, given that the pilot would be seated facing upward and theground would be behind their head at this stage. Unlike some other tailsitteraircraft, the pilot's seat was fixed in the direction for forward flight. Thespinning rotor would also obscure rear vision.

This design was unique among 20th-century VTOL craft, and other German conceptcraft. However, some early design studies for the Rotary Rocket Rotonspacecraft in the 1990s showed a free-spinning rotor with tip-driven rotorsproviding lift.

In the 1950s, the US built prototype tailsitter aircraft (the Lockheed XFV, and Convair XFY Pogo), but these were powered by conventional turboprops, withnose-mounted contra-rotating propellers to counter torque. They also usedconventional wings for lift, though their cruciform tails with integral landinggear were broadly comparable to the Triebflügel. (Wikipedia)

(Luftwaffe Photo)

Focke-Wulf Triebflügeljäger, experimental project (model).