Focke-Wulf Fw Triebflügel 

Nazi flag Germany (1944)
Experimental VTOL Fighter – Paper Project

The bizarre looking Focke-Wulf Triebflügel fighter design. [luft46.com]
During the war, German aviation engineers proposed a large number of different aircraft designs. These ranged from more or less orthodox designs to hopelessly overcomplicated, radical, or even impractical designs. One such project was a private venture of Focke-Wulf, generally known as the Triebflügel. The aircraft was to use a Rotary Wing design in order to give it the necessary lift. Given the late start of the project, in 1944, and the worsening war situation for Germany, the aircraft would never leave the drawing board and would remain only a proposal.

History

During the war, the Luftwaffe possessed some of the best aircraft designs and technology of the time. While huge investments and major advancements were made in piston engine aircraft development, there was also interest in newer and more exotic technologies that were also being developed at the time, such as rocket and jet propulsion. As an alternative to standard piston engine aircraft, the Germans began developing jet and rocket engines, which enabled them to build and put to use more advanced aircraft powered by these. These were used in small numbers and far too late to have any real impact on the war. It is generally less known that they also showed interest in the development of ramjet engines.

Ramjets were basically modified jet engines which had a specially designed front nozzle. Their role was to help compress air which would be mixed with fuel to create thrust but without an axial or centrifugal compressor. While this is, at least in theory, much simpler to build than a standard jet engine, it can not function during take-off. Thus, an auxiliary power plant was needed. It should, however, be noted that this was not new technology and, in fact, had existed since 1913, when a French engineer by the name of Rene Lorin patented such an engine. Due to a lack of necessary materials, it was not possible to build a fully operational prototype at that time, and it would take decades before a properly built ramjet could be completed. In Germany, work on such engines was mostly carried out by Hellmuth Walter during the 1930s. While his initial work was promising, he eventually gave up on its development and switched to a rocket engine insead. The first working prototype was built and tested by the German Research Center for Gliding (Deutsche Forschungsinstitut für Segelflug– DFS) during 1942. The first working prototype was tested by mounting the engine on a Dornier Do 17 and, later, a Dornier Do 217.

The Dornier Do 217 was equipped with experimental ramjets during trials. [tanks45.tripod.com]
The Focke-Wulf company, ever keen on new technology, showed interest in ramjet development during 1941. Two years later, Focke-Wulf set up a new research station at Bad Eilsen with the aim of improving already existing ramjet engines. The project was undertaken under the supervision of Otto Ernst Pabst. The initial work looked promising, as the ramjets could be made much cheaper than jet engines, and could offer excellent overall flying performance. For this reason, Focke-Wulf initiated the development of fighter aircraft designs to be equipped with this engine. Two of these designs were the Strahlrohr Jäger and the Triebflügel. The Strahlrohr had a more conventional design (although using the word conventional in this project has a loose meaning at best). However, in the case of the Triebflügel, all known and traditional aircraft design theory was in essence thrown out the window. It was intended to take off vertically and initially be powered by an auxiliary engine. Upon reaching sufficient height, the three ramjets on the tips of the three wings would power up and rotate the entire wing assembly. It was hoped that, by using cheaper materials and low grade fuel, the Triebflügel could be easily mass-produced.

A model of the Triebflügel. This is how it may have looked if completed. [Wiki]

The Name

Given that these ramjet powered fighter projects were more a private venture than a specially requested military design, they were not given any standard Luftwaffe designation. The Triebflügel Flugzeug name, depending on the sources, can be translated as power-wing, gliding, or even as thrust wing aircraft. This article will refer to it as the Triebflügel for the sake of simplicity. 

Technical Characteristics  

Given that the Triebflügel never left the drawing board, not much is known about its overall characteristics. It was designed as an all-metal, vertical take-off, rotary wing fighter aircraft. In regard to the fuselage, there is little to almost no information about its overall construction. Based on the available drawings of it, it would have been divided into several different sections. The front nose section consisted of the pilot, cockpit, and an armament section for cannons and ammunition, which were placed behind him. Approximately at the centre of the aircraft, a rotary collar was placed around that section of the fuselage. Behind it, the main storage for fuel would be located. And at the end of the fuselage, four tail fins were placed. 

A drawing of the Triebflügel’s interior. [luft46.com]
This aircraft was to have an unusual and radical three wing design. The wings were connected to the fuselage while small ramjets was placed on their tips. Thanks to the rotary collar, the wings were able to rotate a full 360o around the fuselage. Their pitch could be adjusted depending on the flight situation. For additional stability during flight, the tail fins had trailing edges installed. The pilot would control the flying speed of the aircraft by changing the pitch.  Once sufficient speed was achieved (some 240 to 320 km/h (150 to 200 mph)), the three ramjets were to be activated. The total diameter of the rotating wings was 11.5 m (37  ft 8  in) and had an area of 16.5 m² (176.5 ft²). 

This unusual aircraft was to be powered by three ramjets which were able to deliver some 840 kg (1,1850 lb) of thrust each. Thanks to ramjet development achieved by Otto Pabst, these had a diameter of 68 cm (2.7 ft), with a length of less than 30 cm (0.98 ft). The fuel for this aircraft was to be hydrogen gas or some other low grade fuel. The estimated maximum speed that could be achieved with these engines was 1,000 km/h (621 mph). The main disadvantage of the ramjets, however, was that they could not be used during take-off, so an auxiliary engine had to be used instead. While not specifying the precise type, at least three different engines (including jet, rocket, or ordinary piston driven engines) were proposed.

In the fuselage nose, the pilot cockpit was placed. From there the pilot was provided with an overall good view of the surroundings. The main issue with this cockpit design wass the insufficient rear view during vertical landing. 

Close up view of the Triebflügel landing gear assembly. [Secret Jets of the Third Reich]
The landing gear consisted of four smaller and one larger wheels. Smaller wheels were placed on the four fin stabilizers, while the large one was placed in the middle of the rear part of the fuselage. The larger center positioned wheel was meant to hold the whole weight of the aircraft, while the smaller ones were meant to provide additional stability. Each wheel was enclosed in a protective ball shaped cover that would be closed during flight, possibly to provide better aerodynamic properties. It may also have served to protect the wheels from any potential damage, as landing with one of these would have been highly problematic. Interestingly enough, all five landing wheels were retractable, despite their odd positioning.  

The armament would have consisted of two 3 cm (1.18 in) MK 103s with 100 rounds of ammunition and two 2 cm (0.78 in) MG 151s with 250 rounds. The cannons were placed on the side of the aircraft’s nose. The spare ammunition containers were positioned behind the pilot’s seat.

Final Fate

Despite its futuristic appearance and the alleged cheap building materials that would have been used in its construction, no Triebflügel was ever built. A small wooden wind tunnel model was built and tested by the end of the war. During this testing, it was noted that the aircraft could potentially reach speeds up to 0.9 Mach, slightly less than 1,000 km/h. The documents for this aircraft were captured by the Americans at the end of the war. The Americans initially showed interest in the concept and continued experimenting and developing it for sometime after. 

In Modern Culture 

The Triebflügel taking off in the movie. [marvelcinematicuniverse.fandom.com]
Interestingly, the Triebflügel was used as an escape aircraft for the villain Red Skull in the 2011 Captain America: The First Avenger movie.

Conclusion

The Triebflügel’s overall design was unusual to say the least. It was a completely new concept of how to bring an aircraft to the sky. On paper and according to Focke-Wulf’s engineers that were interrogated by Allied Intelligence after the war, the Triebflügel offered a number of advantages over the more orthodox designs. The whole aircraft was to be built using cheap materials, could achieve great speeds, and did not need a large airfield to take-off, etc. In reality, this aircraft would have been simply too complicated to build and use at that time. For example, the pilot could only effectively control the aircraft if the whole rotary wing system worked perfectly. If one (or more) of the ramjets failed to work properly, the pilot would most likely have to bail out, as he would not have had any sort of control over the aircraft. The landing process was also most likely very dangerous for the pilot, especially given the lack of rear view and the uncomfortable and difficult position that the pilot needed to be in order to be able to see the rear part of the aircraft. 

The main question regarding the overall Triebflügel design is if it would have been capable of successfully performing any kind of flight. Especially given its radical, untested and overcomplicated design, this was a big question mark. While there exist some rough estimation of its alleged flight performances, it is also quite dubious if these could be achieved in reality. The whole Triebflügel project never really gained any real interest from the Luftwaffe, and it is highly likely that it was even presented to them. It was, most probably, only a Focke-Wulf private venture.

Triebflügel Estimated  Specifications

Rotating Wing diameter 37  ft 8  in / 11.5 m
Length 30 ft / 9.15 m
Wing Area 176.5 ft² / 16.5 m²
Engine Three Ramjets with 840 kg (1,1850 lb) of thrust each
Empty Weight 7,056  lbs / 3,200 kg
Maximum Takeoff Weight 11,410 lbs / 5,175 kg
Climb Rate to 8 km In 1 minute 8 seconds
Maximum Speed  621 mph / 1,000 km/h
Cruising speed 522 mph  / 840 km/h
Range 1,490  miles / 2,400 km
Maximum Service Ceiling 45,920 ft / 14,000 m
Crew 1 pilot
Armament
  • Two 3 cm MK 103 (1.18 in) and two 2 cm (0.78 in) MG 151 cannons

Gallery

A rendition of how the Triebflugel may have looked had it been built. Illustration by Pavel ‘Carpaticus’ Alexe.

Credits

  • Article by Marko P.
  • Duško N. (2008)  Naoružanje Drugog Svetsko Rata-Nemačka. Beograd.
  • D. Sharp (2015) Luftwaffe Secret Jets of the Third Reich, Dan Savage
  • Jean-Denis G.G. Lepage (2009) Aircraft of the Luftwaffe 1935-1945, McFarland and Company  
  • J.R. Smith and A. L. Kay (1972) German Aircraft of the Second World War, Putham  
  • http://www.luft46.com/fw/fwtrieb.html 

 

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.