Annular wing

Air Classics, Dec 2001 by Gacon, Jean-Yves

In the August issue, Jim Thompson presented "Flights of Fancy" - a weird assortment of aeronautical creations "that never saw air beneath their wings." The annular wing concept featured in the drawing from the Kaman design office did, in fact, give way to a real machine which flew, albeit briefly, during 1959 in France.

State-owned Nord Aviation (which later merged with other companies to form Aerospatiale, now part of EADS) conducted, as did so many others, studies during the mid-1950s on the feasibility of turbojet VTOL aircraft in association with the engine manufacturer SNECMA. The concept retained by the technical director of SNECMA (M. Oestrich) was that of a tail-sitter aircraft powered by a single powerful 8150-lb thrust Atar.

The annular wing configuration, devised by engineer von Zborowski, was retained. Test pilot Auguste Morel flew at first on top of a test bed consisting of a bare vertical turbojet War volant) with an ejection seat, to investigate the low speed performance and controllability in the vertical mode. The results were excellent and the P2 version of the strange craft was even publicly demonstrated at the Salon du Bourget in June 1957.

The next step was the realization of an aircraft capable of vertical takeoff and transition to horizontal flight while fitted with an annular wing. The experimental machine was the SNECMA C450 Coleoptere and it was delivered in April 1958. It was a single-seater that weighed in at 6600-lb loaded, was 26.3-ft long (the diameter of the annular wing was 10.5-ft) and power came from a 8200-lb thrust SNECMA Atar 101E turbojet.

After long bench testing and several flights under a crane, the first untethered flight took place on 5 May 1959. This was for a duration of 3 minutes and 38 seconds with Morel at the controls. Some rotations were attempted during the sixth flight. The maximum height attained was 2700 feet and the total flight time (including tethered trials and ground power trials) was 20 hours, 40 minutes.

On the ninth flight, disaster struck. Auguste Morel climbed to 3100 feet, successfully rotated the craft 54 degrees, then back to attempt a slow descent in flight transition. Uncontrollable oscillations took place followed by a fast descent in an almost horizontal attitude. Having lost control, Morel ejected at 160 feet and was severely injured. The craft was totally destroyed.

No attempts were made to resume the program, which initially envisaged a ramjet-powered interceptor and even a commercial aircraft. In retrospect, with a marginal excess power/weight ration and the modest stability devices of the era, it was probably too ambitious. But, it was an annular wing - and it flew!

Jean-Yves Gacon gacon@wanadoo.fr