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Aviation History
1952
1952 - 0220.PDF
92 FLIGHT HELICOPTER HISTORY Mr. L. H. Hay ward's Lecture to the Heli copter Association: Recent Jet-drive Designs ON Friday, January nth, Mr. L. H. Hayward delivered to the Helicopter Association of Great Britain a paper entitled "A Review of Helicopter Patents." He described a number of his torical experiments made up to about the beginning of the cen tury; then, because helicopter patents are so numerous, he con fined the remainder of his review to jet-drive developments. Last week we gave a digest which carried the story up to the middle of World War II; in this second instalment the remainder of the review is summarized. Mr. Hayward is patents engineer to the Fairey Aviation Co., Ltd. SHOWN in Fig. 8 are three drawings from two American patents of 1943, filed by L. H. Leonard. The remark able machine illustrated was intended to change its attitude through 90 deg after take-off: it had a fuselage sup ported upon the ground in an upright position by a landing gear retractable in flight to form a streamlined tail cone. Around the fuselage were four surfaces which could be regarded as either wings or rotor blades, with combustion jets mounted at their tips. The main difference between the two patents was that in one case these surfaces were sta tionary during horizontal flight, behaving as wings, while in the second patent they acted as rotor blades at all times during which the machine was airborne. Fins embodying control-surfaces aided stabilization during vertical flight and could be retracted into the fuselage as required. The patentee claimed that by operation of these control surfaces it would be possible to adjust the machine from a vertical to a horizontal flight attitude, and also to counteract the bearing friction of the rotor and thus prevent the fuselage from rotating about its longitudinal axis. The pitch of the rotor blades could be altered in flight as desired. This type of helicopter was known as an "axial-flow" type, the rotor airflow remaining axial in all conditions of flight. Mr. Hayward then went on to describe a British patent filed in 1944 by a Frenchman, M. de Chappedelaine. Draw ings from the patent, one of which is shown in Fig. 9, showed the arrangement adopted to extract the boundary layer from the rotor blades. The rotor, which was mechanically driven, was provided with a venturi ejector at the tip of each of its two blades, each venturi being ducted to create a depression within the opposite blade. The blade interior was vented to the surface by slots through which the boundary air was bled. The patentee claimed that his rotor was more efficient than one of normal design. A British patent was granted to the Fairey company in Fig. 8. The "axial-flow" helicopter patented by Leonard in 1943. There were two forms- ef this project, one having a rotor which behaved as e fixed wing when the aircraft was in steady flight. June, 1944, in respect of a helicopter rotor driven by gas turbines mounted at the blade tips. The patent drawings (Fig. 10) do not specify any particular type of gas turbine, the one shown having an annular combustion chamber and a divided airflow, part of the flow being used for bearing cooling. Fuel lines and ignition leads were carried through the main spar of the blade. Both turbojet and turboprop units were shown in this specification. Mr. Hayward then described a number of late war-time patents embodying free-piston gas generators, jet-drive units geared down to the rotor, rotors with telescopic blades and rotors with heat-exchanging jet systems. He then discussed another of Stalker's many (and pro gressively more complex) jet-helicopter patents. In this 1946 design, air, compressed by centrifugal force, was ducted to the outer half of the rotor blade and exhausted through slots in the rear upper surface. Part of this airflow was taken past fuel injection nozzles and igniters before ejection through the slot. In the cross-section of the blade (Fig. 11) can be seen the flap over the ejection slot which controlled the outlet flow. The slot could be adjusted by this means to give a variable exit area for the hot gases from that part of the internal flow in which fuel had been burnt. The blade also incorporated a trailing-edge flap, seen hinged at lower right in the figure, for altering the cyclic pitch. A practical patent of 1946, in the name of the Cierva Autogiro Co., Ltd., was of interest by virtue of the fuel sys tem specified. A highly volatile fuel was to be used, de livered as vapour through the rotor hub and blades to tip- jets, a reducing valve being inserted in the supply line so to control the delivery pressure as to prohibit re-condensation of the fuel due to centrifugal compression. By the use of this system, it was stated that fuel atomizers would be eliminated, together with the high centrifugal pressures experienced in fluid-supply pipes in the rotor blades, while (left). M. de Chappedelaine's design, embodying boundary- layer suction on the rotor blades. Fig. 10. (te/ow). The tip-mounted turboprop and turbojet specified by the the Fairey company in a patent of 1944.
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