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Aviation History
1961
1961 - 0176.PDF
Frontal area of the Rover T.P./70 (or 90), seen above with cowlings off and on, is smaller than that of the Currie Wot's fuselags. It could comfortably replace a Cirrus Minor engine in an Auster or Gemini "Flight" photogmphs Rover's 90 h.p. Turboprop . . . will be able to approach at high r.p.m. but low power and attainovershoot power simply by changing pitch without having to speed up the turbine. Throttle lag will then be almost eliminated A pitch-setting lever will be provided in the cockpit, but will beused virtually in the same way as a pitch lever with a conventional constant-speed propeller.The construction of the turbine unit itself closely corresponds to that of the industrial and a.p.u. version; and the relevant compon-ents and figures for the developed T.P.90 are enumerated below. ROVER T.P.90/1 The T.P.90 is a single-shaft turboprop, arranged as an engine-changeunit complete with variable-pitch propeller and all standard accessories. Two lateral intakes pass air to the single-sided centrifugal compressor,which handles a maximum mass-flow of 1.881b/sec with a pressure ratio of 2.8, at 46,000 r.p.m. Fuel is injected downstream into the single combustion chamber (see drawing) and the efflux escapes through thesingle-stage turbine machined from a forged blank of Nimonic 105. Gas temperature behind the turbine is 650°C at full power at sea level. At maximum r.p.m. the output shaft speed is 2,525 r.p.m., and asnoted in the text a hydraulically controlled propeller is scheduled to be used. Engine control is effected by a simple mechanical system, withautomatic overpower and top-temperature limits. Fuel is supplied by a Rover multi-piston pump with a full-load pressure of 2501b/sq in andmaximum pressure of 6001b/sq in. A return-type oil system is used, the tank being integral with the compressor housing. Standard acces-sories, included in the weight given bslow, are: electric starter and 12V supply system, d.c. generator, oil cooler, variable-speed throttlecontrol, tachometer, j.p.t. indicator, ammeter, oil-pressure warning system, variable-pitch propeller, spinner and backplate. Overall length of powerplant, 48.6in with propeller and spinner or30.1in without; wid:h, 20in; height, 27.5in; weight with propeller and all standard accessories, 2351b; power/weight ratio, 0.383 b.h.p./lb;power ratings, max take-off, 120 b.h.p. at 47,000 r.p.m.; max cruise. 90 b.h.p. at 46,000 r.p.m.; fuel specification, DERD 2482 or 2486,diesel oil or kerosine; specific consumption at max cruise rating, 1.38; oil grade, SAE 10; oil consumption, O.lpt/hr. AUSTER FOR BOUNDARY-LAYER RESEARCH XJIGH lift through boundary-layer control is the theme behind*--* the research work being done by Professor W. A. Mair and Dr M. R. Head in the Cambridge University aeronautics labora-tories. They hope to be able to double the maximum lift coeffi- cient, and so reduce both the take-off and landing speed of anaircraft and its ground run. Preliminary tunnel work consisted of a thorough investigationinto the properties and causes of the turbulence in the layer. The mean speed of the air in the layer was measured by the hot-wiremethod, in which the current required to keep the wire at a constant temperature gives an indication of the cooling effect, andthus of the speed. Readings were converted electronically into a linear output signal which was integrated over a period of timeto give a true mean speed. Theories for the causes of separation were developed from a conical diffuser with a lateral slit, and froma flat perforated plate. In the former case the effective angle of the diffuser was adjusted by means of movable centre bodies, toachieve critical separation. The amount of pressure or depression through the slit required to produce or suppress separation couldthen be measured. When all these tests had been successfully concluded the time had come, as Professor Mair said, "to suck itand see." The Ministry of Aviation—under whose contract part, butnot all, of this work is being done;—provided an Auster for flight test. Before Marshall Flying Services started to modify it for thepurpose of the experiments, basic tests were imde to provide a datum against which later results could be compared. The suction is provided by a single-stage axial impeller drivenby a 60 h.p. Budworth shaft turbine engine mounted behind the pilot's seat. Both impeller and engine exhaust vertically down-wards from the underside of the fuselage just below the trailing edge. An entirely new wing has been fitted, of considerablyincreased span and aspect ratio. Ducting has been installed in the wing to suck the boundary layer from an area extending rightacross the span from the leading edge to about 15 per cent chord, and from five full-span strips about l|in wide. There is alsoprovision to suck from two strips each on the flaps and ailerons. Of perforated plywood, the strips are covered with paper untilthey are to be used. The tailplane and fin have been enlarged, and the formeris now all-moving under hydraulic power derived from a hand- charged accumulator. Its total movement of about 25° is adjustedby a fully variable control in the centre of the cockpit. The elevators are still controlled from the stick.Flap movement has been increased to 80° and the ailerons now droop almost as much. Spoilers have been fitted immediatelybehind the rear spar. Like the ailerons, these are controlled from the stick, except that a four-position lever in the cockpit allowsthe pilot to select either all spoiler, all aileron, or two intermediate ratios of both. They are expected to be really effective only at largeflap angles, when they will produce large rolling and yawing movements. At the moment the additional instrumentation consists solelyof that concerned with the turbine engine, plus a multiple manometer. An emergency spin-recovery parachute has beenfitted in accordance with Government regulations. Professor Mair expects that this will never be removed; it will be almost impos-sible to spin with all possible configurations of flap angle and suction rate. All these modifications have increased the weight and dragseverely, and at present Dr Head is working on reducing the latter by improving the streamlining. A new wing-root-to-canopyjunction has been fitted, the wheels spitted, wing and under- carriage bracings faired, and the top of the fuselage straightened.A new airscrew has been fitted to improve the rate of climb. Professor Mair explains that the secret of high lift lies inincreasing the stalling angle. The stall is caused by air in the boundary layer stopping and starting to move forward. He hopesto prevent this by continually removing the boundary layer. Dr Head, who won a DSO and DFC during the war, will pilotthe aircraft himself. SIMPLER HIGH-SPEED FLIGHT PROBABLY unrivalled in the making of technical documen-taries, Shell Film Unit have completed a new film in their High-Speed Flight series—a simplified condensation of Abfroach-ing the Speed of Sound (1956), Transonic Flight (1957) and Beyond the Speed of Sound (1959). In colour, and with a care-fully-pared and well-spoken commentary, High Speed Flight (Simplified Version), runs for about 20 minutes, enabline thewhole background to the airflow pattern changes to be explained more quickly than was possible with the more detailed andspecialized films that preceded it. Considerable use is rmde of animated diagrams and theSchlieren photography technique (the latter is the subject of another excellent film, Schlieren, made by the same unit in 1959).Concentrated technical description is interspersed with some pood —if now rather dated—air-to-air photographic sequences, inciud-ing quite alarming shots of a Vampire pitching and a Meteor snaking as compressibility effects are encountered. The film, which was compiled by Denis Segaller, is available on loan in 35mm and 16mm sizes.
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