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Aviation History
1955
1955 - 0863.PDF
FLIGHT, 24 June 1955 861 WITHOUT VISIBLE MEANS of SUPPORT Ultra-Modern French Entomology — the Coleopter By A. R. WEYL, A.F.R.Ae.S.* Hanneton II WINGLESS aeroplanes with retractable fuselages and"suffused" powerplants would form lovely playgrounds for the gadget maniacs, who could hang their baubles on them and/or bury colossal electronic edifices within them. Closely approaching this dream of the frustrated aircraft designer comes the coleopter. Coleoptere means "beetle"; but at first sight, this aerial vehiclelooks rather more like the Martian stage-coach of a "night- starvated" science-fiction writer, or perhaps like an animated wind-sock. Yet this airborne propulsive duct is an aeroplane indeed, andactually the product of sound design-philosophy for which highly qualified aeronautical engineers claim responsibility; at present theFrench Government handles part of the development, and an entire entomological family of military and civil projects followingthe basic conception is under active development (see table, p. 862). The basic idea underlying the coleopter is to utilize the lift ofan annular (ring-shaped) wing which houses and guides the propulsive jet (i.e., airscrew or thermal gas-jet, as the case maybe). But before we deal with the engineering aspect of this radical approach, something should be said about the people behind it, allGerman technicians settled in France, each with 20 to 30 years of practice in aeronautical engineering research. Inventor and head of the B.T.Z. (Bureau Technique Zborowski,Brunoy, France) is Dipl-Ing. H. v. Zborowski, formerly in charge of B.M.W. rocket development and responsible for the existence ofthe nitric acid/aniline motor (widely used in guided missiles). The aerodynamicist is Dr. W. Seibold, well known from workin German and French research establishments. The structural expert, Professor Dr-Ing. H. Hertel, has a world-wide reputationas former technical director of Heinkel as well as of Junkers; in these connections his name is associated with such notable designsas the first single- and twin-jet-engined aeroplanes (He 178 and He 280 respectively); the fastest pre-war rocket aeroplane (He 176);and the first multi-jet bomber (Ju 278). People like this are not propagandists of science-fiction; they are experimenters buildingupon sober facts. B.T.Z. coleopter development began in 1950 and includesmuch wind-tunnel and model research. Since 1952, the Societe Nationale d'Etude et de Construction des Moteurs d'Aviation(S.N.E.C.M.A.), directed by Professor Dr-Ing. H. Oestrich, has collaborated actively with B.T.Z. in experimentation and develop-ment. Last year, the French Air Minister was shown a free-flying controlled model. In aircraft development, we are now passing out of the stageof fitting airframes with propulsion devices. The next and final stage will be the complete "melting together" of sustentation andpropulsion into indivisible units. Known possibilities include the jet-propelled wing, the flapping wing, the paddle wing, and thetiltable and lifting rotor. We know, too, that jet lift can replace wing or rotor lift. None of these amalgamations, however, has asyet produced an entirely satisfactory solution. The standard aeroplane renders sterling service for high-speedflying. The attainment of really high speed is, however, limited by the wing area needed for take-off and landing, and the speedrange is restricted by the existence of a stalling speed. The latter, in turn, dominates the characteristics of take-off and landing,because the aeroplane has to be horizontally accelerated or de- *The author states that he is obliged to the firm of B.T.Z.—in par-ticular to Dipl-Ing. H. v. Zborowski and Dr. W. Seibold—and also to Professor Dr-Ing. H. Oestrich of S.N.E.C.M.A.) for the technical infor-mation quoted and for the illustrations. THE curious "coleopter" is one of the first types of vehicle in whichboth structure and powerplant are integrated. In some respects these aircraft resemble the "flying barrel" machines of the 1920-1930 era, inwhich a propulsive airscrew was mounted inside an annular duct; but, unlike these, the coleopter employs the annular duct as the solegenerator of lift in cruising flight. A comparison could also be drawn with the recent American Hiller ducted-fan helicopter; but the lattermaintains its major axis sensibly perpendicular. Most of the interest in coleopters centres upon the French Bureau Technique Zborowski, andin these pages a well-known aeronautical engineer outlines their work. celerated up to or down from this minimum speed of sustentation.High-speed flying is, therefore (and whatever flap-fiddlers may say), unavoidably linked up with high stalling speeds. The consequences of high stalling speeds are expressed inlandscapes obliterated by huge aerodromes covered with miles of concrete runways; in elaborate undercarriages, flaps, air brakes,etc.; in undesirable circumstances and unpleasant incidents. All this was thoroughly appreciated and bewailed years ago, yet noserious attempts were made to curb the evil at the source. It took the advent of the helicopter to make people realize thatsuggestions for vertical ascent and landing were not preposterously absurd. We possess powerplants light enough for the vertical elevationof practical aircraft and odd furniture, by direct jet lift. For an aeroplane with aerodynamically lifting wings this means that wingloading and wing shape are no longer dominated by the require- ments of take-off, climb, and/or landing. A winged engine, how-ever, need not be practical for military use because of conditions imposed by manoeuvrability in turning flight. The stalling speedof a wing limits the diameter of the narrowest turn, and the aero- plane of standard configuration must bank. With guided missiles,therefore, cross-wing arrangements are preferred as soon as stress is laid upon turning manoeuvrability. The annular coleopter wing is characterized by an internal flowduct, thin aerofoil section and low aspect-ratio. In addition to aerodynamic lift, the propulsive jet produces a lifting componentwhen at incidence (incidence in this case is referred to the direc- tion of gravity, and for the purposes of this discussion, lift canbe regarded as a force opposed to gravity). This jet lift may, according to the angle which the duct axis assumes against thedirection of gravity, range from zero to a force equalling (or exceeding, for climb) the weight of the aeroplane. Consequently,the coleopter has a speed range which extends from maximum (or diving) speed right down to zero speed, vertically and hori-zontally. There is no limitation by a stalling speed. When the aerodynamic incidence of the wing—against thedirection of motion—approaches its critical value (separation of flow, with subsequent loss of aerodynamic lift), the loss of lift iscompensated by jet lift, i.e., by the lifting component of the thrust. The novelty of the coleopter conception is covered by numerouspatents held exclusively by v. Zborowski. Arrangements to pro- duce or guide a propulsive jet within a tubular duct have, however,often been proposed or tried; the ducted airscrew, for instance, actually goes back to G. Koch's aeroplane project of 1893, anda ducted-fan-propelled aeroplane was built by H. Coanda in 1911. Annular duct-like wing systems, though without a propulsive jetinside, were characteristic of Giraudan's tandem aeroplane of 1909. Nearly all coleopter projects show a central body or fuselagecentrally within the duct, extending from it in the forward direc- tion. This fuselage houses the propulsive plant and the pilot(or automatic guidance). The pilot, and any passengers, are in seats that tilt for the transition from vertical to horizontal flight,
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