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Aviation History
1938
1938 - 2091.PDF
JULY 21, 1938. FLIGHT. 63 disconnects the feathering pump line from the airscrew and nlacts the governor back into the system, and the airscrew runs again at the speed for which the governor is set by the pilot in the cockpit. For normal constant-speed operation the Hydromatic air screw requites two simultaneous sources of oil supply; one from the constant-speed control booster pump and the other oil under normal pressure from the engine oil system. Referring again to the sequence diagrams, oil from the constant- speed control pump A is permitted to enter the hollow drive gear shaft B of the governor and thence is taken to the air screw shaft when the engine is turning faster than the speed for which the governor is set by the pilot in the cockpit. Governor oil is thus metered at the top port of the drive gear shaft, and enters the rotating airscrew shaft by means of the oil transfer rings C. It then follows the same path desciibed above, for the oil during the feathering operation, to the in board side of the piston. At the same time, oil from the engine lubricating system under normal engine-oil pressure enters the airscrew mechanism through the supply pipe D in the centre of the airscrew shaft, and reaches the outboard side of the piston through ports J and K. The governor oil pressure builds up until it exerts a force greater than the sum of forces which oppose motion of the piston outward into the front of the dome. These forces are: (r) Engine oil pressure times the effective piston area; (2) the net blade twisting force consisting of the blade centrifugal twisting moment modified by the aerodynamic twisting moment; (3) friction of the moving parts of the airscrew mechanism. The net blade twisting force is transmitted from the blade gear segment L to the rotating cam M, and through the cam rollers N acting in the slots of the rotating cam, to the piston. The blade centrifugal twisting moment is a moment acting on the airscrew blade around its longitudinal axis in the direction of a decrease of blade angle. It is the result of a force couple consisting of the resultants of components of centrifugal force acting on the mass of the airscrew blade on either side of the blade's longitudinal axis. The aerodynamic twisting moment is usually opposite in direction to the blade centrifugal twisting moment being caused by the position of the resultant centre of pressure of the aerofoil section of the £1,500,000 Extension at Bristol AN important announcement was made by the Air Ministry last Monday about the establishment of further '' ex pansion" factories. One is the carburettor "shadow" factory, to be operated at Coventry by the Standard Motor Co., Ltd., and already referred to in Flight. The other is the first of a new series of extensions to existing factories, for which Government assistance -will be given. The works of the Bristol Aeroplane Company will be the first to be expanded under this scheme, and £1,500,000 extensions are being put in hand immediately. Death of a Pioneer Pilot VLIGHT records with very sincere regret the death of one of Denmark's earliest pilots, Robert Svendsen. Mr. Svendsen, with some friends, was rowing out to a yacht off Copenhagen; the boat capsized, and he was drowned. Robert Svendsen, Who was 53, bought a Voisin biplane and, in 1910, succeeded in flying across the Sound from Den mark to Sweden. Afterwards he gave demonstration flights in various Danish provincial towns and was also the first man to fly across the Lim Fjord at Aalborg. Two of his contem poraries, Alfred Nervo and Ulrich Birch, have also passed away, Nerv'o through illness and Birch in ah accident on a Maurice Farman before the war. Unlike many of the early pilots, Robert Svendsen soon abandoned flying and took to the much more prosaic livelihood of manufacturing stoves. He can probably be regarded as having been Denmark's pilot No. 1, although Mr. Eilehammer, who is still alive and is an engineer and not a pilot, is reported to have made a flight of sorts ''nit; before Svendsen went to France to learn the art there. Courageous, but . . . T-\ odd contrast to Howard Hughes' carefully planned flight •*• with three companions was last Monday's unheralded solo Atlantic crossing from New York to Baldonnel (Dublin) by Douglas Corrigan, flying an eight-year-old Curtiss Robin fligh ting monoplane (165' h.p. Wright Whirlwind five-cylinder J&dial)-, Corrigan took 28 hr. 13 min.—4 hr. 17 min. less than Col; Lindbergh. blade in front of the centre of rotation of the blade (the blade's longitudinal axis). In normal level flight this aerodynamic moment is relatively small. When the governor oil pres sure builds up to a force on the piston just greater than the sum of these three forces the piston starts to move out toward the front of the dome, and engine oil in front of the piston is displaced back into the engine lubricating system. This out ward movement of the rotating cam increases the pitch of the blades and the engine speed is this reduced. As the engine slows down to the speed for which the constant speed conhol is set, the pilot valve in the governor descends to the position shown in the top view of the governor, thereby shutting off the top port of the drive gear shaft and cutting off the supply of governor oil from the booster pump to the airscrew. The oil under pressure from this pump, of course, then goes through the relief valve back to the engine. Should the engine r.p.m. fall below the speed for which the governor is set, the pilot valve in the governor descends still further, opening the bottom of the drive gear shaft to drain. F^ngine oil in the dome at the outboard side-of the piston is always, during normal airscrew operation, under pres sure from the action of the engine oil pump. This pressure acts as if a spring were placed between the outer end of -^he piston and the front of the dome, the spring, however, having the unusual characteristic of exerting a constant force regard less of the amount of its compression. The blade centrifugal twisting moment, aided by this "spring" force, moves the piston inward overcoming friction and the back pressure exist ing in pushing governor oil back through the governor to drain. As the pitch of the blades thus decreases, the engine speed picks up and the pilot valve in the governor is raised, closing off the drain through the drive gear shaft just as the engine reaches the speed for which the governor is set. The relief valve in the governor is so interconnected with the engine oil system that the valve is held closed by the force of its spring plus the engine-oil pressure. Thus the effect is to provide a maximum pressure differential across the airscrew piston equal to the setting of the relief valve spring and the effect of variations in engine-oil pressure in any one engine or between engine types are eliminated. More than 500 hours of ground testing have been completed with Hydromatic airscrews, and more than 4,000 hours of test flying have been logged. Theory and Practice "'Flight' Handbook," by W. O. Manning, V.R.Ae.S., and the technical staff of "Flight" ; 35. 6d. (by post, 3s. gd.), Dorset House, Stamford Street, London, S.E.i. H ERE is a book which will satisfy the requirements of every one seeking a grounding in the broad principles of flight and wanting to acquire elementary knowledge of modern air craft design and construction. To give a brief outline of the contents, the book starts with an explanation of the broad principles of flight, without resort to mathematics, and goes on to discuss the differences between monoplanes, biplanes, tractors, pushers, iandplanes, flying boats, etc. Having thus sketched in a basis, Mr. Manning proceeds to examine in some detail—still virtually without mathematics and with the aid of simple diagrams—the reasons why wings lift and controls operate, going on from that to deal with such matters as skin friction and reduction of drag. Next he explains modern structural methods, and then reviews various components such as airscrews, undercarriages, braking systems and controls. Another section is devoted to engines and their methods of installation, w-hile a particularly informative one explains the working of instruments. Other chapters are concerned with gliders and their operation, bal loons and airships. Outstanding among the illustrations are some of Max Millar's notable cut-away drawings of modern aircraft. Saro Scholastic Successes IN the, recent A.F.R.Ae.S. examinations three junior members of the Saunders-Roe staff were successful. One achieved the distinction of three first places, and is the first to receive the recently founded Major Baden-Powell Memorial Prize. Also, in the April examinations for the National Certificate in Engineering, ten of the firm's apprentices were awarded certificates in aeronautical engineering. Saunders-Roe have in operation an apprentices' technical training scheme, consisting of part-time day courses in aero nautical engineering, conducted in the firm's school, and co ordinated with evening courses at Cowes Evening Institute.
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