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Aviation History
1949
1949 - 1678.PDF
4-12 FLIGHT, 29 September 19-19 AIR-COMPRESSOR IMPROVEMENTS IN the British aircraft industry the name Hymatic is synony-mous with air compressors, and in this connection it isnoteworthy that the basic design of the Hyraatlc com- pressor has remained unchanged despite an increase in gener- ating capacity from 300 lb/sq in to 1,000 lb/sq in. There has. nevertheless, been a coincident demand for im- proved performance in output and ability efficiently to pump at high altitudes, and during the past lour years the company has undertaken considerable research in an endeavour to meet such requirements. This work first resulted in a unit designed for a supercharged supply from a gas-turbine compressor, and the soundness of the new basic design was proved after extensive tests on engines and gearboxes and on the Mamba-Balliol. It was subsequently found, however, that when treated as a nor- mally aspirated unit but fitted with a smaller inter-stage cooler, the new compressor offered considerably improved performance characteristics by comparison with its predecessor. Develop- ment work was then concentrated with the aim of producing a single basic compressor which could be available for use either as a supercharged or normally aspirated unit, depending on the cooling arrangements adopted. The compressor which resulted from this research has now satisfactorily passed its type test and, designated S50U, fol- lows to some extent the established Hymatic practice in employ- ing a two-stage single cylinder with truncated piston. Thermal efficiency has been improved to the extent of fjf.ving an increase of 35 to 55 per cent in performance (depending on the pressure) for a corresponding weight penalty of less than 15 per cent. Other modifications in design have indicated during the test programme that at least twice the life between overhauls (in comparison with the well-known Hymatic SH6 series compres- 1.000 800 L600 !400 LEVEL :30.000ft. 10 20 25 TIME (mm.) 30 45 Comparative performance curves of pressure generation against pump-up time at sea level and 30,000ft for the standard SH6/I0 and new S50 U Hymatic compressors. Hymatic Two-stage Intercooted Unit Rated for 1,000 ib/sq in : Develop- ment work on 3,000 Ib/sq in Type sor can be achieved), whilst pumping to full pressure can lie maintained above 40,000ft. In point of fact, pressure genera- tion falls only to 650 lb/sq in at an altitude of 49,000ft. As an aid in obtaining improved performance at altitude, the poppet inlet-valve has been replaced by a very light and simple ring valve. In the SH6 series compressor, the compressed air delivered by the first stage was passed to the second stage annulus by a transfer valve and so, consequently, was hot; cooling of the compressor was, therefore, critical when working at the higher pressures, and the cruising r.p.m. had to be dropped from 1,500 to 1,200 if an economical life at 1,000 lb/sq in was to be obtained. By the introduction of inter- stage cooling in the S50U design, however, the air is delivered to the second stage at as little as 50 deg C. As a result, higher speeds can confidently be accepted without reduction in com- pressor life, and, for 1,000 lb/sq in generation, the standard speed of 1,500 r.p.m. can be retained. It has been found that the best compromise on intercooler design is a simple coiled pipe which is capable of accom- modating varying expansions without imposing undesirable loads on either the cooler or cylinder. Another advantage is that employment of the cooler permits the compressor to be boosted from the cabin-pressurization supply, such an added constant output being of particular use for serving windscreen wipers and automatic controls. In the new S50U compressor the master relief valve has been incorporated in the delivery-valve assembly so that a beneficial weight-saving can be made in pipe joints and mounting. In addition, a magnesium crankcase of a more rigid design has been adopted. Current development work by the company is devoted to a three-stage compressor based on the S50U design, intended for a generating capacity of 3,000 Ib/sq in. Data have been gained leading to the design of a larger unit intended for aircraft installation, and work on these prototypes has shown that 3,000 Ib/sq in can well be adopted for ram operating pressures. FOLLOWING an account of the activities of the TurkishAir League's aircraft factory at Ankara, published in Flight of March 24th, 1949, recent information indicates that Turkey is now pursuing a policy of concentrating on nationally designed aircraft rather than on one of producing those of German or Russian origin. Prominent among new develop- ments are the T.H.K.14, a side-by-side two-seat primary training glider; the T.H.K.2, a single-seat powered aircraft, fully aerobatic; and a twin-engine light transport, the T.H.K.5A. Dakota conversions for Turkish State Airlines, and approximately 100 Miles Magisters (being built under licence), are also being handled by this factory. Work is proceeding on two new designs—the T.H.K.12, a 12-passenger feederliner powered by two 600 h.p. Pratt and PROGRESS IN TURKEY National Designs Predominant Bearing a strong resemblance to the French S.E.C.A.N. Courtis, ;V the T.H.K. 11 pusher is now ; undergoing flight trials at Ankara. ": Whitney R1340 radial engines, and the T.H.K. 15, a two-seat tandem all-metal primary trainer bearing a resemblance to the De Havilland Chipmunk; it is hoped to produce the T.H.K.15 in quantity for the Turkish Air Force. Flight trials are in progress with the T.H.K.13, a flying- wing type of glider intended basically for aerodynamic research A powered version is also projected. A prototype T.H.K.11, almost identical with the French Courlis—a twin- boom four-seat pusher—is now in the flight-testing stage. Production of engines is being undertaken by a new factory at Ankara and although to date only De Havillancl Gipsy Majors have been built under licence, the Turkish Air League is aiming at the eventual large-scale production of nationally designed piston engines and gas turbines. W. G. F 12
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