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Sunday, October 11, 2009

Sunday Ship History: Early Vertical

It was the Germans who started it.

As the Allied bombing campaign began to take its toll on German airfields and industry, Focke-Wulf called up a concept fighter named the Triebfugel. The Triebflugel had a most unusual design - the "wing" rotated about a stationary body:

The design was particularly unusual. It had no wings, and all lift and thrust were provided by a rotor/propeller assembly in the middle of the craft (roughly halfway between cockpit and tailplane). When the plane was sitting on its tail in the vertical position, the rotors would have functioned similarly to a helicopter. When flying horizontally, they would function more like 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. To start the wings spinning, simple rockets would have been used. As the speed increased, the flow of air would be sufficient for the ramjets to work and the rockets would expire. The pitch of the blades could be varied with the effect of changing the speed and the lift produced. There was no reaction torque because the rotors were free-spinning. Fuel for the ramjets was carried in fuselage tanks, and was piped through the centre support ring and along the rotors to the jets.

A cruciform empennage at the rear of the fuselage comprised four tailplanes, fitted with moving ailerons that would have also functioned as combined rudders and elevators. The tailplane would have provided a means for the pilot to keep the fuselage from spinning in case of a slight friction against the rotor ring as well as controlling flight in pitch, roll and yaw.

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

When taking off the rotors would be angled to give lift as with a helicopter or more accurately a gyrodyne. Once the plane had attained sufficient altitude it could be angled into level flight. This required a slight nose-up pitch to give a downward thrust as well as primarily forward thrust - the rotors would have provided the only significant lift. Consequently, the four cannons in the forward fuselage would have been angled slightly downward in relation to the horizontal centre line of the fuselage.

To land, the craft had to slow its speed and pitch the fuselage until the craft was vertical. Power could then be reduced and it would descend until the landing gear rested on the ground. This would have been a tricky and probably dangerous manoeuvre given that the pilot would be seated facing upward and the ground would be behind his head at this stage. Unlike some other tailsitter aircraft, the pilot's seat was fixed in the direction for forward flight. The spinning rotor would also obscure rear vision.

See also here and here.

The Triebfugel was not the only German VTOL design there was also the Heinkel "Wespe":
The Wespe was designed around a circular wing, with small wing tips protruding beyond the circular wing at the two lower wing support locations. A single He S 021 turboprop (the turboprop development of the He S 011 jet engine), driving a six-bladed propeller, provided 2000 horsepower plus 750 kp thrust and was fed by an air intake located below the cockpit. The Wespe took off and landed on three landing gear, which in flight were covered for aerodynamical purposes. The pilot sat in a normal seated position in the nose under a huge blown canopy, and two MK 108 30mm cannon mounted in blisters on each side of the cockpit were envisioned for the armament.
The Heinkel Lerch:
The "Lerche" (Skylark) employed a ducted wing planform with contrarotating propellors, powered by two Daimler Benz DB605D engines. The pilot lay in a prone position in the extreme nose, and projected armament was two MK 108 30mm cannon.

Then there was the Focke WulfSchnellflugzeug, a ducted fan VTOL fighter:
But perhaps Focke’s greatest achievement was the development of the “turbo shaft” propulsion system currently utilized by the majority of all the world’s helicopters.

As soon as he had the relevant data for the new German jet engines Focke started design work on the Focke-Wulf Schnellflugzeug (Fast Aircraft) which was nicknamed the Rochen (an aquatic ray-skate).

In 1939 he patented the idea of a circular aircraft with a large aerofoil section and an open center that acted as a huge propeller duct for twin counter-rotating propellers driven by a projected Focke-Wulf designed turbojet engine via an axis and gearbox.
From here:

A high performance fighter which could take off and land vertically, like a helicopter! No more need to depend upon elaborate and vulnerable airfield facilities in time of war. Every paved highway, even every level patch of farmland suddenly capable of launching a cloud of fighters to deal with an invading army. And more! Fighter protection at sea which doesn’t require huge aircraft carriers- -every destroyer, even every transport and oiler, capable of carrying one or two fighters of its own! Such an aircraft would present any attacker with enormous difficulties and therefore would help mightily to preserve the world’s peace.

In the late 1940s and early 1950s the US Navy sought to develop an aircraft that could take off and land vertically, eliminating the need for large aircraft carriers, and providing instantly available of air support for landing troops. It was thought that the best way to provide this was with a tailsitting aircraft, and the newly developed turboprop was to be used since supersonic speed was not necessary.

Runways and big deck carriers being juicy cold war targets, the U.S. Navy and the Air Force looked into vertical take off fighters like the Ryan X-13 Vertijet and the XFY-1 Pogo, perhaps the most famous of early VTOL designs because it actually worked:


The U.S. Navy also thought about aircraft carrying nuclear submarines carrying VTOL aircraft, as set out here:




As we all know now, the VTOL effort has never stopped, though some of the early ideas have faded, perhaps to be seen again...

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