Doblhoff WNF 342
| Doblhoff WNF 342 | |
|---|---|
 Doblhoff WNF 342 V4 in 1:11 scale in the helicopter museum in Bückeburg |
|
| Type: | Experimental helicopter |
| Design country: | |
| Manufacturer: | |
| First flight: |
September 1943 |
| Number of pieces: |
3 (V1, V2, V3 / V4) |
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The Doblhoff WNF 342 was an experimental helicopter made by Wiener Neustädter Flugzeugwerke (WNF) in the 1940s. This was the first helicopter to fly with a recoil engine in the form of a hot blade tip propulsion.
history
The development of the WNF 342 was based on a drive concept developed by the Austrian Baron Friedrich von Doblhoff between 1937 and 1939, during his student days. By orienting himself more towards the structural design of gyroscopes , the complex and heavy structure of the rotary wing designs of the time was to be avoided. The rotor blades should not be driven from the inside by shafts and gears, but from the outside by a jet drive in the blade tips. The first theoretical and experimental work was aimed at using the rotating rotor blades as a compressor and thus avoiding a motor-driven compressor unit. Because of the low compression that can be achieved with it and the resulting low thermal efficiency, this mechanically simplest solution was not pursued any further.
A development contract from the Reich Aviation Ministry for a test vehicle (WNF 342) came about through personal intervention by Doblhoff in Berlin. Spending until the end of the war was limited to 300,000 Reichsmarks.
In September 1943 the machine was completed and took off for the first time in a tethered flight in a hall of the WNF. In the autumn of 1943, an eight-minute free hovering flight was also possible at an altitude of between one and three meters. Shortly afterwards, Plant 1, where the development department was also active, was destroyed by an Allied bombing raid. The V1 was so badly damaged that only a few parts were reusable. From the remains of the V1, the V2 was created, while the following V3 was rebuilt and later converted into the two-seater V4. Until the end of the war it was not possible to transition from hovering to level flight.
Versions
V1
For the first flying development vehicle (WNF 342 V1), a 60 hp Walter Mikron motor was used , which drove the centrifugal compressor of an Argus As 411 engine and thus provided the necessary compressed air. At the same time, a mixture of vaporized fuel and air was injected into the nozzles directly behind the compressor, passed through the rotor and the rotor blades and ignited with glow plugs in the combustion chambers at the blade ends. The fuel-air mixture ratio was chosen to be stoichiometric (ratio of air: fuel 14: 1) in order to achieve the greatest possible performance. The disadvantage here were high temperatures, which led to red-hot nozzle walls. The combustion chambers therefore had to be made of high-strength, alloyed steels.
Due to the additional combustion of the compressed air, the power achieved in the rotor can be higher than the power of the compressor motor itself. A disadvantage compared to a pure shaft drive is the roughly three times higher fuel consumption. Doblhoff saw a solution in using the compressor motor to drive a propeller in horizontal cruise flight. In this phase, the rotor should only run in autorotation mode, so that the long cruise flight as a gyroplane could be done with significantly lower fuel consumption.
V2
Instead of the Walter Mikron motor, a 90 HP Walter Minor was used in the V2 to drive the As-411 charger. As a pure test vehicle for the blade tip drive, neither the V2 nor the V1 had a propeller to generate the propulsion. The V2 showed signs of the ground resonance phenomenon for the first time due to the increased rotor speed . The V2 was badly damaged in an accident in 1944.
V3
Simultaneously with the testing of the V2, construction work on the V3 was carried out, with which the transition to flight as a gyroplane was also to be demonstrated. The V3, with its double tail girders and the detachable pusher propeller, received a significantly different design than the V2. To solve the problem of inadequate directional control in hovering flight, a small additional pusher propeller was provided, which directed its air jet towards the rudder. The V3 was powered by a 135 hp Argus As-8 engine to drive the As 411 charger that was still in use .
In the first attempts at hovering, the V3 showed, even more than the V2, a tendency to swing upwards. The engineer Kurt Hohenemser, who was called in as a consultant and responsible for aerodynamics and dynamics at Flettner, identified the slight difference between the natural frequency of the rotor blades and the rotational frequency of the rotor as the cause. In an accident related to this problem, in which the hull began to vibrate beyond control, the V3 was severely damaged but could be rebuilt.
V4
To demonstrate the practical usability of the test vehicle, the V3 was converted into the two-seater V4 towards the end of 1944. Even before the first hover, the war events with the approaching front forced the V4 to be relocated from Ober-Grafendorf to Zell am See . The flight attempts were not resumed before the arrival of the US Army .
Whereabouts
After the war ended u. a. Colonel Charles Lindbergh visits the helicopter. The V4 was shipped by the Americans as spoils of war on the HMS Reaper to the USA and was given the registration FE-4615 (Foreign Evaluation 4615, later T2-4615). Baron von Doblhoff followed in the same year to the USA. The machine was later handed over to General Electric in Schenectady, New York, and was last observed in 1949.
Technical specifications
| Parameter | V1 | V2 | V3 / V4 |
|---|---|---|---|
| Number of seats | 1 | 1 | 1 (V3) 2 (V4) |
| Rotor diameter | 8 m | 8 m | 9.96 m |
| rotational speed | 305 min −1 | ||
| Empty mass | 250 kg | 340 kg | 430 kg |
| Max. Takeoff mass | 640 kg | ||
| Engine | a Walter Mikron with 60 HP (44 kW) | a Walter Minor with 90 PS (66 kW) | an Argus As 8 B with 135 HP (100 kW) takeoff power |
literature
- Kyrill von Gersdorff, Kurt Knobling: helicopter and gyrocopter (Die deutsche Luftfahrt Volume 3) , Bernard & Graefe Verlag, Munich, 1982, ISBN 3-7637-5273-0 , pp. 61-68
- AERO - The illustrated compilation of aviation (aircraft from A – Z) . Book 65, Marshall Cavendish, 1984, p. 1816
Web links
- www.aviastar.org: Doblhoff WNF-342 (English)
- Excerpt from an original film about a WNF 342 flight on Youtube
- Doblhoff WNF 342 V4 as a 1:11 model in the helicopter museum in Bückeburg
Individual evidence
- ↑ Description of As 411, p. 16f ( Memento of the original from August 9, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. accessed on July 27, 2014
- ↑ Hermann Hinterstoisser: The end of the war in Pinzgau. Hans Bayr et al .: Salzburg 1945–1955. Destruction and reconstruction (pp. 41–55). Salzburg: Salzburg Museum Carolino Augusteum, ISBN 3-901014-43-8 .
- ^ German Warplane Survivors of the Second World War
