Dornier Do 31

Do 31
Dornier Do 31 in 1968
Role	VTOL transport
Manufacturer	Dornier Flugzeugwerke
First flight	10 February 1967
Status	Project cancelled April 1970
Primary user	German Air Force
Number built	3

The Dornier Do 31 was a West German experimental VTOL jet transport built by Dornier. The Do 31 was designed to meet a NATO specification (NBMR-4) for a tactical support aircraft for the EWR VJ 101 VTOL strike aircraft designed under the NATO contract of BMR-3. The project was cancelled in 1970 owing to high costs, technical problems and a change of requirement.

Design and development

In the early 1960s, the German Air Force became increasingly concerned that its airfields were vulnerable to air attack from Eastern Bloc forces and actively researched the possibility of dispersed operations which included flying from Autobahnen but required aircraft with STOVL capabilities. Part of these trials involved the modification of German F-104 Starfighters to be rocket-launched from stationary ramps in what became known as the ZELL program. The Starfighters were to be recovered to short strips using aircraft carrier-type arresting gear. The Do 31 was intended to use the same strips as forward operating bases.

When the high cost, technical and logistical difficulties were realized, the German Air Force ceased trials involving VTOL aircraft such as the Do 31, VJ101, and the later VFW VAK 191B which resulted in the cancellation of these projects and further use of these aircraft was limited to research purposes only.

Initial designs incorporated a Bristol Pegasus vectored-thrust turbofan in each of the two inboard nacelles and four Rolls-Royce RB162 lift engines in each of the outer nacelles. It was planned to dispense with the outer nacelles and their engines when larger RB153 turbofans (of approximately 5,000 lbf (22 kN) thrust) became available. By mounting the engines in pods, the fuselage could provide a capacious hold with a rear loading ramp.

In all, three test prototypes were built, these being E1, E2 and E3 - the "E" indicating Experimentell (Experimental). E1 was powered only by the Pegasus engines, and was designed to test horizontal flight. E2 was a static test airframe, and did not fly. E3 had both Pegasus and RB162 lift engines installed, and was designed to test the vertical flight mode. The first prototype (E1) first flew on 10 February 1967 with just the two Pegasus engines. The third prototype (E3) flew in July 1967 with all ten engines fitted. The first hovering flight took place on 22 November 1967. Full forward and backward transitions were made in December 1967.

The Do 31 established several Fédération Aéronautique Internationale (FAI) world records during its ferry flight to the 1969 Paris Air Show.

Do131

It was the first, and so far only, vertical takeoff jet transport ever built. The project was cancelled in April 1970, although it made its final public flight on 4 May 1970 during the ILA in Hanover. One of the factors that led to the cancellation was the large drag and weight of the lift engine pods which reduced the useful payload and range compared to conventional transport aircraft.

To cope with the complex and fast computations necessary for vertical takeoff, the Do 31 was equipped with a Dornier DO-960 hybrid computer.

A development of the Do 31, called Do 131 with twelve or fourteen liftjets, was explored, but no prototype was built.

Aircraft on display

Do 31 E3 on display at the Deutsches Museum Flugwerft Schleissheim

Both flying prototypes have been preserved in Germany, but the fate and current location of the non-flying testbed (E2) is not known.

• Dornier Do 31 E1, D-9530, is preserved and displayed at the Dornier Museum Friedrichshafen.
• Dornier Do 31 E3, D-9531, was initially put into storage at Oberpfaffenhofen, then for several years on display in the open in the courtyard of the Deutsches Museum in Munich and after restoration is now on display at the Deutsches Museum Flugwerft Schleissheim at Oberschleissheim near Munich

Operators

Artist drawing

Germany

• German Air Force (Luftwaffe)

Specifications (Do 31E)

Flight deck of the Do 31

Data from Jane's all the World's Aircraft 1969–70, The Observers Book of Aircraft

General characteristics

• Crew: 2
• Capacity: 36 fully-equipped troops / 24 stretchers / 3,000–5,000 kg (6,600–11,000 lb) payload
• Length: 20.88 m (68 ft 6 in)
• Wingspan: 18.06 m (59 ft 3 in)
• Height: 8.53 m (28 ft 0 in)
• Wing area: 57 m² (610 sq ft)
• Airfoil: root: NACA 64A412.5 ; tip: NACA 64A410
• Empty weight: 49,500 kg (109,129 lb)
• Max takeoff weight: 60,500 kg (133,380 lb)
• Fuel capacity: 8,000 L (2,100 US gal; 1,800 imp gal) in five integral wing tanks
• Powerplant: 2 × Rolls-Royce BE.53/2 Pegasus 5-2 vectored thrust turbofans, 69 kN (15,500 lbf) thrust each in underwing pods
• Powerplant: 8 × Rolls-Royce RB.162-4D turbojet engines, 20 kN (4,400 lbf) thrust each vertically mounted in optional wing-tip pods

Performance

• Maximum speed: 730 km/h (450 mph, 390 kn)
• Cruise speed: 650 km/h (400 mph, 350 kn) at 6,000 m (20,000 ft)
• Range: 1,800 km (1,100 mi, 970 nmi) with maximum payload
• Service ceiling: 10,700 m (35,100 ft)
• Rate of climb: 26.667 m/s (5,249.4 ft/min) all engines

19.2 m/s (63 ft/s) Pegasus engines only

See also

Aircraft of comparable role, configuration, and era

• Armstrong Whitworth AW.681
• LTV XC-142

Related lists

• List of military aircraft of Germany

Further reading

• Jackson, Paul A. (1976). German military aviation, 1956-1976. Hinckley, Leicestershire, UK: Midland Counties Publications. ISBN 0-904597-03-2.
• "V/STOL YEAR A Review of Progress by Rolls-Royce Jet Lift". Flight International. Volume 8 (Number 2859): p.p.1031-1034. 26 December 1963. Retrieved 22 April 2019. {{cite journal}}: |issue= has extra text (help); |volume= has extra text (help)