Dornier Thu 31

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Dornier Thu 31
Dornier Do 31 in 1968.jpg
Type: V / STOL transport aircraft
Design country:

GermanyGermany Germany


Dornier works

First flight:

February 10, 1967


Flight tests ended in 1970

Production time:

Was never mass-produced

Number of pieces:


The Dornier Do 31 was a German vertical take -off cargo aircraft .


1959 started the first preparations, and in February 1962, the aircraft manufacturer was Dornier commissioned the Do 31 as a battle zone transport the 25-ton class to transport 36 fully equipped troops for the Air Force of the Armed Forces to develop. In the first phase, the development program was limited to the construction of two hovering frames, two airworthy prototypes and an Iron Bird for testing the systems. In the 2nd phase, the Do-31 should have been developed for series production. At the end of the first phase, the program was no longer pursued. From the point of view of many experts, it was discontinued too early because NATO's military guidelines had changed. The entire Do-31 program cost just over 200 million DM , 40% of which went to British companies, mainly for the development of the engines. The main and cruising engine Pegasus 5-2 was developed by Bristol-Siddeley (later: Rolls-Royce ) and also used in the British Harrier vertical take-off.

The technically very demanding development and testing program was carried out by a remarkably small development and test team.

Three prototypes were built (SG, E-1, E-3); but only the E-1 and E-3 should fly. The SG (floating frame) was only intended for tests on the ground. The prototype E-1 (D-9530) had its maiden flight on February 10, 1967. The second prototype, the E-3 (D-9531) carried out its (conventional) maiden flight on July 14, 1967 and took off on September 22 1967 for the first vertical take-off. On December 16, 1967, the aircraft went from vertical to horizontal flight for the first time.

Thu 31

In 1969 the E-3 was transferred from Oberpfaffenhofen near Munich to the Aerosalon in Paris , and five new world records were set for vertical take-off aircraft; including the one for the highest speed of 514 km / h, flown by pilot Drury W. Wood and copilot Dieter Thomas. On May 5, 1970, the Do 31 flew one last time in front of an audience at the International Aerospace Exhibition in Hanover , although the project had already been stopped in October 1969.

After 154 test flights and a total of 39 flight hours, the E-3 was shut down and stood in front of the main entrance on the Museum Island of the Deutsches Museum in Munich for a very long time . After the completion of the Flugwerft Schleissheim , it was transported there in 1996, restored and can now be viewed there.

After 101 test flights and a total of 59 flight hours, the E-1 was also decommissioned in 1970, stored and transported from Oberpfaffenhofen to Friedrichshafen in April 2009 . It has been exhibited there since July 2009 in the new Dornier Museum .

Vertical take-off and level flight

View into the gondola of the lift engines on the left wing

The aircraft takes off vertically using eight lift engines and two cruise engines equipped with swiveling thrusters. In addition, there is a steering nozzle at the stern that can blow out upwards or downwards. The two cruise engines are used in level flight.

In order to be able to use the fuselage for transport purposes, the lift engines (Rolls-Royce RB 162) are housed in the characteristic nacelles at the wing tips, four on each side. These gondolas can be removed so that additional containers can be installed in their place.

Flight testing

The development and flight testing of the Do 31 was carried out step by step with four different test vehicles:

  • A controller test frame (RVG) to create the specification for the flight controller and the control kinematics. This tubular lattice frame with four lifting engines carried out tests tied to a column and in free hover.
  • A large hovering frame (SG) for testing the on-board systems, for examining the control properties in hovering flight and for developing suitable processes for vertical take-offs and vertical landing. Except for the fuselage, which was designed as a tubular grid construction and did not have a tail unit, the cockpit, wings, engines and lifting gondolas were already originally designed. The fuselage was provided with segments in the area of ​​the wings in order to test the effect of exhaust gas jets deflected back from the floor in terms of heat and vibration.
  • An experimental aircraft (Do 31 E-1) for conventional flight tests, i.e. H. Runway take-off, runway landing and level flights. This aircraft did not have any lift engines in the nacelles.
  • An experimental aircraft (Do 31 E-3) for the vertical take- off test.

In addition, a rupture cell for strength tests at IABG in Ottobrunn , a system test bench ( Iron Bird ) in Immenstaad for the on-board systems and a soil erosion test bench for investigating the durability of natural and artificial soils (landing and take-off sites) under the impact of the engine exhaust jet were built. The soil erosion test rig was a height-adjustable engine mounted on a low-loader. Experiments were carried out on different soils and airfields.

Since at least the two e-aircraft were equipped with ejection seats for the pilots, bullet tests were also with a Martin-Baker - ejection seat performed.

The entire flight program was completed without an accident. This is remarkable because other international vertical takeoff projects resulted in some serious fatal accidents.

In the feature film Nine Lives the Cat (1968) by Ula Stöckl shows parts of the twentieth test flight of the Do 31.


  • April 1964: First free flight of the RVG
  • January 11, 1967: SG's first free flight
  • February 10, 1967: First conventional flight of the E-1
  • July 14, 1967: First flight of the E-3
  • February 28, 1968: First VTOL circuit of the E3 with complete take-off and landing transition

The program was a great technological success and showed the full efficiency of the Dornier works, which were rebuilt after the war . However, it did not come to a series because the Bundeswehr changed the procurement plans and said goodbye to the VTOL concept for transport aircraft. It was followed by a "follow-up" at NASA in 1970 before the program was finally discontinued. NASA and astronaut Neil Armstrong rated the Do-31 as "convincingly positive". On October 31, 1969, the contract between Dornier and the Federal Office for Defense Technology and Procurement expired .

Technical specifications

Drawing of the Thu 31
Cockpit of the Dornier Do-31-E3 D-9531
Parameter Data
length 20.70 m
Span over everything 18.06 m
Wingspan wing 17.14 m
height 8.53 m
Wing area 57 m²
Wing extension 5.2
Wingspan of horizontal stabilizer 8.0 m
Tailplane area 16.4 m²
Wingspan rudder unit 4.4 m
Vertical tail surface 15.4 m²
Hull length 19.5 m
Trunk width 3.10 m
Torso height (rear) 3.25 m
Length of loading space without ramp 9.2 m
Loading space width on the floor 2.12 m
Loading space height 2.2 m
Loading area or ramp 19.5 m²
Loading volume or ramp 50.0 m³
loading 5 t payload, e.g. B. 36 fully equipped soldiers
Empty mass 13,868 kg
Max. Takeoff mass 24,500 kg (V / STOL 21,000 kg)
Max. Landing mass 21,800 kg (V / STOL 21,000 kg)
Top speed 750 km / h
Summit height 10,700 m
Range 1800 km
March engines two Bristol Siddeley Pegasus 5–2 with 69 kN (7035 kp) each
Lift engines eight Rolls-Royce RB.162-4D with 19.6 kN (2000 kp) each

Preserved copies

The Do 31 E-3 is located in the Schleissheim aircraft yard ; the Do 31 E-1 in the Dornier Museum in Friedrichshafen.


Thu 31 E-3 in the Schleissheim aircraft yard

When the Dornier Do 24 ATT was developed, landing gear actuation cylinders were urgently needed - they were taken from the Do 31 E-3 in the Deutsches Museum to save time and money. At least these two parts of Do 31 still fly around the world in the truest sense of the word.

In order to be able to solve the mathematical problems of the very complex VSTOL design, Dornier developed its own hybrid computers such as the Dornier DO-960 .

In the alternative reality of the television series “The Man in the High Castle”, the representatives of the GNR use the Do-31 (without a designation) as a transport plane.

See also


  • DGLR : The German vertical take-off aircraft. 2000, ISBN 3-932182-10-3
  • Mike Rogers: VTOL Aircraft - Vertical Takeoff. Motorbuch Verlag, Stuttgart 1992
  • Otto E. Pabst: short and high flyers. Bernard & Graefe Verlag Koblenz 1984
  • Peter Steinmüller: Steep ascent, hard landing , in: VDI nachrichten 9/2017, p. 27, here:
  • Peter Kielhorn: Dornier Do 31 , Motorbuch Verlag, Stuttgart 2018, ISBN 978-3-613-04096-0

Web links

Commons : Dornier Do 31  - Collection of images, videos and audio files

Individual evidence

  1. Ula Stöckl in the taz about the use of the recordings of a test flight in her feature film. Retrieved July 14, 2019 .
  2. ^ The DO 31. In: Retrieved September 28, 2017 .
  3. Bernd Ulmann: The Dornier DO-960 Analog Computer. In: December 19, 2005, accessed May 2, 2020 .