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Aviation History
1955
1955 - 1502.PDF
612 FLIGHT, 14 October 1955 The Maximum Speed of the Helicopter . . . leads to large power and payload losses if the rotor is unloaded andleft to autorotate or if it is tilted through a right angle to act as an airscrew. It is suggested that the logical solution is to unloadonly that portion of the disc where the flow conditions are detri- mental to higher speeds, and the stiff-hinged rotor is suggested asa means of doing this. It is shown in Ref. 1 that the stiff-hinged rotor has the additional advantages of making a helicopter statically and dynamically stable, in which it is unique, and thatit permits virtually indiscriminate distribution of the payload. References (1) P. R. Payne. The Stiff-hinged Rotor. Aircraft Engineer-ing, October 1955. (2) P. R. Payne. High Offset Flapping-Pin Analysis.Aircraft Engineering, November 1954. (3) P. R. Payne. Booster Ramjets for Helicopters. Flight,December 31st, 1954. Helicopter Vibration LAST Friday, October 7th, a lecture entitled "The Control ofJ Helicopter yibration" was read before the Helicopter Associa- tion of Great Britain by the author of the article above, Mr. P. R.Payne. In this paper he provides one of the most valuable overall pictures of the helicopter-vibration scene yet to bepublished. He discussed structural vibration caused by periodic displace-ment of the rotor hub under two separate headings: vibration which is due to a degree of unbalance in the rotor and that whichis fundamental to a balanced rotor. The latter was shown to be unavoidable, but it could be minimized by increasing both thetip-speed and the number of blades above present-day values. Other factors which could help were the choice of a high disc-loading and blade weight, the elimination of drag hinges, the use of a high offset flapping pin and the employment of two or moremain rotors. The use of drag hinges led to a general increase ia the magnitude of all in-plane vibration harmonics, withthe exception of the first relative to rotor axes which, with a two-blade rotor, caused second-harmonic structural vibration. It was demonstrated that first, or higher, harmonics of forcefluctuation on the blade could be balanced out by suitable inclina- tion of the mechanical axis, and the lecturer suggested that thisremedy, coupled with the use of moderately high offset flapping hinges, was preferable to the technique of off-loading the rotor(s)on to fixed wings. The paper then introduced an elementary theory of rotor un-balance, in order to demonstrate the physical causes of first- harmonic structural vibration. From the results was built up arational method of rotor balancing. In the second half of Mr. Payne's paper the general theory ofcontrol vibration was discussed; particular attention was paid to the system in which a Hafner torque-bar was used in place of themore conventional torsion bearing. The consideration of the basic causes of vibration enabled a method of eliminating vibration to beestablished, and the lecturer also suggested various modifications to present techniques. AUTAIR IN AUSTRIA BEFORE any large-scale civil engineering project is undertakenit is usual to ascertain the soil stability, and—in the case of such structures as dams—the suitability of the sub-strata. InAustria, the Malta Valley region has recently become a hive of activity, various large projects being under way including theconstruction of a large dam at the 6,000ft level and hydro-electric power station with a design output reported to be no less than 500million kW (500,000 kW is more probable). In order to explore the region surrounding the dam site heavydrilling rigs were needed to be taken up through the exceedingly rugged valley. After six months of futile efforts with donkeys andporters it was decided that at least a year would be needed to lift the equipment, if in fact it could be done at all. Nevertheless, thefirm of Autair, Ltd., of Croydon Airport, were approached, and their European associate company, Overseas Aviation, directedby Mr. R. Myhill, agreed to take the contract on. Flying was to be carried out by the company's chief pilot, Capt. LincolnLord, and the chief engineer, Mr. W. Shippey, was also to be on hand. Some 20 tons of gear had to be lifted to the head of the valley,and a strong belly beam and special nylon nets had to be devised to enable the Dragonfly to lift the heavy machine parts and drilltubes. Capt. Lord then flew a shuttle service between the foot of the valley and the dam site, taking both gear and personnel. The entire job was done in two weeks, in some 50 return flightseach of about 30 minutes' duration. Thus, the main hydro-electric project has gone ahead on schedule. Pleasant though the surroundings may have been, Autair's Austrian contract was arduous. Second from the left in the group is Lincoln Lord, Autair chief pilot. The Malta Valley is shown below, right
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