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Aviation History
1961
1961 - 0407.PDF
FLIGHT, 30 March 1961 415 Air Transport and V/STOL BREGUET'S GENERAL MANAGER DELIVERS THE 14th BLERIOT LECTURE THE 14th Louis Bleriot Lecture was delivered in London onMarch 23 by General Henri Ziegler, general manager ofthe Breguet company. His subject was The Development of Short-range Air Transport Through the Use of VjSTOL Aircraft. The first part of General Ziegler's paper dealt with criteria forthe development of short-range air transport. Under the heading "Flexibility of Operation" he said:"The operation on a somewhat extensive scale of short-haul traffic requires the establishment of an overall network broken downinto a large number of loading points in order to ensure the appro- priate service. Surveys recently conducted have demonstrated thata short-range domestic airline can serve communities within 60 statute miles radius around each airfield. This figure, actually,must be reduced if a convenient railway station is available in the vicinity. Thus a large number of intermediate stops are necessaryfor the type of service expected from the airlines. This extension of the number of small airfields for intermediate stops will be possibleonly if the required ground facilities are kept to a minimum and are as simple and as inexpensive as possible. "In the European countries there exists a large number of landinggrounds for light aeroplanes which could be opened to commercial traffic requiring grass strips of some 2,000ft only. For example,in France there are only some ten major airports available for normal scheduled transoceanic or transcontinental flights such asthose operated by the Boeing 707 or DC-8. There are some 20 additional airports large enough for the Viscount class aeroplanes,but there are more than 400 airfields able to cope with V/STOL. Islands and Mountains "In another area of application, the V/STOL transport can serveislands where it is not possible to build large runways, because of the available space, while air service is a first necessity and a publicservice. This approach could solve the traffic problems of Northern Scotland or of the islands in the Pacific. Finally, the V/STOLtransport can open to air traffic many new areas in the mountains. . . "STOL capability, and eventually hovering capability, seem tobe essential to ensure proper safety of operation." General Ziegler went on to consider the various classes of VTOLand STOL aircraft—conventional machines with low wing- loadings, aircraft with boundary-layer control, convertible types,and those with jet lift. He concluded this part of his paper: "... we think, in the present state of the art, that the propeller convertibleSTOL aeroplane gives a satisfactory answer to the proposed service. These conclusions will probably be altered in a few yearsbecause of further technical developments; but I think that a first generation of propeller-driven STOL transport can give a spec-tacular impulse to short-range air traffic." The third section of his paper dealt with French experience,particularly with the deflected-slipstream transport aircraft as represented by the Breguet "94" family. Of particular interest werehis remarks on safety. He thought that Breguet had devoted most effort to achieve a safety level even higher than for conventionalaircraft. General Ziegler said: "It is for this purpose that the mechanical interconnection of the engines and propellers has beenprescribed. The advantages of this system are manifold: (1) In case of engine failure the aircraft remains symmetrical, so that it isnot submitted to the limitations of the minimum control speed. (2) With a four-engined aircraft, if one engine fails the power of theremaining three units is distributed among the four remaining propellers. The propulsion efficiency is somewhat improved andeven though the aircraft is losing 25 per cent of its power, it actually loses only 17 per cent of the slipsteam, that is 17 per cent of thethrust and induced lift. With the interconnection shaft, the four- engined aircraft becomes a "pseudo" six-engine machine. "We have indicated the system in which a large power is main-tained on the engines, while a heavy induced drag is built up by reducing the pitch of the outboard propellers. It so happens thatthis configuration is extremely favourable from a safety point of view, in the case of a baulked landing. If, in this configuration, thepilot wants to fly round again, he can do so immediately by re-equalizing the pitches of the propellers without changing thepower. This gives almost immediately a comfortable rate of climb which can again be increased by partially retracting the flaps (whichdoes not cause any decrease in lift) and by pushing forward the throttle. "Of course, many precautions have been prescribed to avoidasymmetry on the flaps or on the propellers. I will not detail these General Henri Ziegler systems, which are conventional, but 1 would like to comment ondevices specified to overcome failure of the propeller pitch control or of the connecting shaft itself. It is to be emphasized first that thecase of a blade failure is highly improbable, since such failure occurs when the propeller is over-speeding and over-speed isimpossible with the interconnecting shaft." The lecturer showed how the free-wheels and clutches safely over-came any type of failure of the gearboxes or of the shaft system. He went on: "In addition, in case of failure of the propeller pitchcontrol, the blades of the corresponding propeller are automatically locked. Experience has shown that the reserve of differential pitchaction on the symmetrical propeller is sufficient to handle the aeroplane safely. "The studies of these safety systems have been very carefullyevaluated in co-operation with European and American authorities, in order to work out the certification rules for aircraft of this type.I would like to take this opportunity of thanking them all for their assistance and their interest." Discussing problems of operation General Ziegler said: ". . . thisaircraft is easy and safe to handle, if not quite conventional. 1 think, however, that a fundamental characteristic of the STOLtype of aircraft is that of landing accuracy. "Societe Breguet does not intend to develop the STOL transportas an aeroplane as such, but to develop a certain number of auxiliary means which will make it a "transportation system" inthe same sense as one currently thinks of a "weapon system." This is because this family of aircraft is not intended to operate fromexisting airports, but from almost any field. It must be mentioned at this point that the structure and landing gear are designed towithstand rough-ground operation. In co-operation with the European electronic industry, Societe Breguet is developingsimplified but accurate landing aids which should require reason- ably small and inexpensive airborne equipment and a minimumground installation. The aircraft will "haul" itself with a good accuracy and should achieve on small fields a reliability of servicehigher than is currently being obtained on the heavily equipped runways. "This is the family of aircraft to which Societe Breguet is devotingmuch effort. The 941 is now being built in our prototype shops and should fly in a few months." Public Unawareness "As speed has increased, the number of runways able to receivethe new aircraft has decreased because of the tremendous invest- ments necessary to open the required facilities. The air-travellingpublic, therefore, has been limited to people living in major cities or to those travellers who could come to those major cities byground transportation means. "But enormous short-distance traffic is initiated everywhere,not only in big urban areas. It may be stated that, for the present time, an overwhelming majority of the public is quite unaware ofthe advantages of air transportation. The new techniques in the field of STOL and VTOL aircraft are about to give a practical,safe and economical answer to this need for fast local traffic. There is, therefore, an enormous potential market for the transportaircraft of tomorrow. "Of course, procedures for traffic control to ensure safe andreliable service in all-weather conditions must be established and enforced. The corresponding regulations should be prepared with-out delay to answer the growing demand. It must be emphasized, however, that similar problems were involved in launching jettraffic on a large scale and those problems have been adequately solved. "I think, therefore, that I am not making an over-statement insaying that we are going to see, in the near future, a real revolution which will change, not only the traffic distribution of airlines, butalso the economy of the world and even the political situation of many countries. This new tool will open to normal economic lifemany countries having possibilities, but handicapped in their development by the lack of means of transport. I should mentionalso that this new equipment, in its military applications, will also entail radical changes in strategical and tactical concepts, sincemobility through a flexible and fast air transport system will be largely increased, thus solving most of the logistic problems. "Continuous efforts must still be devoted to this new family ofaircraft, but we can be assured, from now on, that the success of this enterprise is within our reach."
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