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Aviation History
1956
1956 - 0355.PDF
355 FLIGHT 30 March 1956 SAUNDERS-ROE SKEETER Development and Construction of the Mark Six THE entry of the Saunders-Roe company into the helicopterfield was made in 1928, when the Helicogyre was builtand tested at the company's works at Cowes. This machine, designed by V. Isaaco, had a distinctive configuration featuring a Bristol Cherub engine mounted at the tip of each of the four rotor- blades. It was later dismantled and shipped to the Royal Aircraft Establishment, Farnborough, where it was re-assembled and tested in the Balloon Shed. This article is concerned, however, with the Mk. 6 Skeeter, powered by the Gipsy Major 201, and its military versions— latest in the Skeeter line and (although not originally a Saunders- Roe design) virtual descendant of the Helicogyre. A brief sum- mary of the development of the Skeeter from the initial design makes an appropriate introduction to our description of this latest , version of the machine. The original Skeeter Mk. 1 was designed by the Cierva company at Eastleigh and, powered by a 106 h.p. Jameson engine, made its first flight on October 8th, 1948. Compared with the Skeeter as it is now known, this machine was smaller, lighter and of somewhat different appearance. The Mk. 2, incorporating an amount of re-design and fitted with the 145 h.p. D.H. Gipsy Major 10, made its first flight just over one year later, on October 20th, 1949. This version did not reach the anticipated performance, and was fol- lowed by the improved Mk. 3, similarly powered. In January 1951 Saunders-Roe took over the facilities and work of die Cierva company at Eastieigh, and formed a Helicopter Divi- sion with Mr. M. J. Brennan responsible for helicopter design. The conversion of the Skeeter Mk. 3 into the Mk. 3B, powered by a 180 h.p. Blackburn Bombardier 702, was the next step in its development. Built under M.o.S. contract, the 3B was intended for Army use; a Naval version, the Mk. 4, was constructed in parallel and was also Bombardier-powered. Mr. T. L. Ciastula, now in charge of the design team of the Saunders-Roe Helicopter Division under Mr. Hugh Gordon (general manager), has described the subsequent Skeeter progress as follows: — "In March 1953, the Skeeter Mk. 3B was sent to A. and A.E.E. fortrials, and in the following month the major obstacle to its development became apparent. The aircraft, under certain operating conditions,proved to be subject to 'ground resonance,' and this characteristic had to be eliminated before any further progress could be made. . . . "The line of attack adopted for the elimination of ground resonanceinline Skeeter was as follows:— "(a) Impedance or 'shaking' tests were conducted to determine thenatural frequencies and the equivalent dynamic stiffness and damping at the hub when it is excited by oscillating forces in the fore-and-aft andlateral directions. "(b) The characteristics of the blade friction-dampers under oscil-lating conditions were determined on a specially constructed rig. Under- carriage damping was also measured. The D.H. Gipsy Major 201 (military version 130) is installed trans- versely in the Skeeter 6, and has been developed to produce its maxi- mum power for periods of up to one hour. Cowlings are removable ;--:• /-/• for flight, if desired. •:•:'• • :?:: "(c) A theoretical analysis was made to determine the instabilityranges for the Skeeter, using the results obtained in the above tests. "(d) The undercarriage and blade friction dampers were re-designedto give satisfactory damping to eliminate the instability. "(e) In parallel with the above programme, full-scale ground-reson-ance tests were conducted in the company's helicopter ground-running compound, with specially designed snubbing arrangements to damp outvibrations of the helicopter when ground resonance was encountered. In these tests, the minima of undercarriage damping and blade damp-ing were determined experimentally and actual ground-resonance was reproduced. "(f) A Skeeter with re-designed undercarriage and blade damperswas subjected to final resonance tests in the compound and, finally, flown through all conditions that experience had shown to be conduciveto ground resonance. . . . "Finally, in March 1954, this aircraft (Skeeter Mk. 5 G-AMTZ) wassent to A. and A.E.E., Boscombe Down, for evaluation trials which con- firmed that it is now free from ground resonance." It should be mentioned that these investigations into the source of the ground-resonance problem, its solution, and the construc- tion of the Mk. 5 civil version with the revised damping and snub- bing arrangements, were carried out at private expense by the company, Ministry of Supply support having been withdrawn in 1953 when the ground-resonance difficulties persisted. The latest version of the Skeeter is powered by the D.H. Gipsy Major 201 engine. In its civil form (G-AMTZ is at present being modified and re-engined in order to obtain a C. of A. for this version) it is known as the Skeeter Mk. 6. The military version of the Major 201 engine is known as the Major 130 and two military Skeeters, thus powered, are now flying. They are prototypes of the Mk. 10 and the Mk. 11 machines designed for the A.O.P. role and as an R.A.F. training helicopter respectively. These two aircraft are owned by the Ministry of Supply, who
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