Rolls-Royce ‘Flying Bedstead’ versus SNECMA ATAR Volant
A bit of a Balancing Act
With my long-standing interest in Short Take-Off Vertical Landing (STOVL) aircraft and my unhealthy infatuation with bizarre flying machines appearance it would be impossible for this article not to happen. Their purpose of both these experimental platforms was the same – the learning how to control a VTOL platform in hovering jet-borne flight and low speed manoeuvres- but which was better?
The appearance of the two flying test beds is radically different, partly due to the differing jet engine designs used, but also due to radical differences in the control systems used. The Flying Bedstead (more properly called the Thrust Measurement Rig, but the name never caught on) was powered by two 5000-lb thrust Rolls-Royce Nene engines mounted back-to-back in a large framework. The jet exhaust for both engines was curved through 90 degrees, so as to act vertically downwards through the centre of Gravity.
One of the exhausts was bifurcated into two nozzles located either side of the other engine’s exhaust, so that if either engine should fail there would be no large moments generated. The pilot’s controls were located on a platform above the apparatus, and the whole was supported on four legs with castoring wheels.
Flight control was delivered through four puffer pipes using compressor bleed air to provide pitching, rolling and yawing moments about the centre of gravity. Height was controlled by varying engine thrust. The whole appearance was quite extraordinary, and can be admired in the preserved example in the Science Museum, London. The exposed framework, long legs, control pipes, and completely exposed unenclosed engines and systems present a wildly unlikely look, and it is easy to see why it acquired the Flying Bedstead nickname.
The aircraft made its first piloted and untethered flight on 3 August 1954, this was the world’s first jet-borne VTOL flight. Numerous other flights were made, and these were generally successful, although vertical height control was tricksy due to the delayed response of the relatively early jet engines to throttle inputs. Knowledge gained from the Flying Bedstead contributed to the design of both the Short SC1 and, through the puffer pipe control system, the Kestrel and Harrier.
The SNECMA C.400 Atar Volant was a step along the development path of the SNECMA C.450 Coléoptère VTOL aircraft, which was a ‘tail-sitter’ featuring an annular wing. The Atar Volant represented the central core of the C.450, and was intended to validate the key propulsion and control system for that aircraft.
After initial trials of the unmanned C.400 P-1, the manned C.400 P-2 made its first free flight on May 14, 1957. Although both test vehicles presented a fearsomely dangerous appearance, there was no similarity between the Flying Bedstead and the Atar Volant. The complex framework of the British design was replaced by a very simple cylindrical body containing the SNECMA Atar 101 engine, with 4 supporting wheeled-legs and puffer pipes for yaw control, and a pilot’s position and ejection seat perched on top of the column.
The control system was novel, and to quote the relevant edition of Janes All the World’s Aircraft (1957-8) was by “jet-deviation, using jets of air bled from the compressor to deflect the main efflux”. It is not entirely clear whether this was a fluidic control system, or whether the air jets were used to deflect vanes within the exhaust nozzle. French sources refer to the use of ‘gas rudders’, which suggests the latter, particularly as the C-450 Coléoptrère is stated to have used vanes in the exhaust for control. The SNECMA C.450 Coléoptère was constructed by Nord Aviation to SNECMA’s designs and made a brief series of 8 test flights before being lost in July 1959, in an accident on its 9th flight, while attempting a transition to horizontal flight.
The contrast in appearance between the Atar Volant and the Flying Bedstead is heightened by the radically different appearance of the fully-enclosed, axial-flow, SNECMA Atar, and the two totally-exposed, centrifugal-flow, Rolls-Royce Nene engines of the latter.
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How to assess these very different machines? The Flying Bedstead has the distinction of being the world’s first jet VTOL aircraft. It generated knowledge which was later used to design the lift engines and control system for the Shorts SC 1, and the hover control system of the Kestrel and Harrier. It presented a bare-bones, misleadingly ramshackle appearance, and its catchy nickname is utterly misleading.
In contrast, the Atar Volant appeared neat rather tidy, with a clever hover control systems. It boasts an alarmingly exposed pilot’s position, furthering its eccentric appeal. Regrettably, like other tail-sitting concepts, the C.450 Coléoptère, the development of which the Atar Volant was supporting, proved to be a dead end. Other French jet VTOL aircraft like the Sud Balzac and the Dassault Mirage III V probably owed more in their concepts to the Shorts SC 1 than the Atar Volant.
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Notwithstanding the appearance and élan of the Atar Volant and its neat exhaust vane control system, I regard the strange, untidy and unlikely-looking Flying Bedstead as more significant because of its greater contribution to understanding the control of jet VTOL aircraft in hovering flight.
Jim Smith