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Aviation History
1955
1955 - 1380.PDF
494 FLIGHT Plessey ram-air turbine. AIRSCREWS de Havilland Propellers. The com-pany's principal new airscrew is a highly efficient turbine airscrew for the 4,000s.h.p. Rolls-Royce RB.109. It has a diameter of 14ft (later to be increased bysix inches), and employs four blades of the solid forged light-alloy type. Thereseems little doubt that this will be the lightest and most efficient unit availablefor this engine, and the whole design seems eminently clean, effective and effi-cient. Flush electric de-icing pads will be fitted and hydraulic pitch-control,feathering, reversing and pitch-locking are provided. Rotol. It has become abundantly clearthat airscrews can utilize solid forged light-alloy blades up to sizes significantlylarger than was believed a few years ago. Rotol's new airscrew for the BristolProteus (and, by inference, most large turboprops) has a diameter of 16ft anda maximum blade chord of 141in, yet has blades of the classic light-alloy type. A fairly typical hydraulic circuit isemployed, although a note should be added regarding the hydraulic lock. Thisis sensitive to overspeeding and to oil pressure. In the event of oil failure thepitch is locked at the position at the point of failure; and, as a further safeguardagainst seal leakage, a solid mechanical flight-safety lock is fitted to keep the pitchat a value still suitable for cruising. The mechanical lock has to be removed bythe self-contained feathering circuit before fine pitch can be obtained. De-icing is of the rebated-blade type,applied over the inner 60 per cent of the radius and taking cyclic current at 208volts, 400 c.p.s. The total weight of the TECHNICAL PROGRESS Some New and Significant Developments Seen in the WITH a total of 307 companies exhibiting this year under the "big top" of theFarnborough exhibition hall, and other wares on view in the outdoor equip- ment exhibition and covered arcades, mental indigestion was indeed assured for anyone rash enough to try to see and absorb everything there of technical merit. On these pages we report on a selection of some of the more interesting develop- ments on view, from which the wide range of this year's products is apparent. blades, with rebating, comes to 486 lband that of the whole airscrew and spinner to 873 lb. These values are quite com-parable to those of equivalent hollow- steel units. The tremendous advantagesof the solid light-alloy unit lie in cost, life, ease of maintenance and, in the firstinstance, ease of manufacture. At a con- servative estimate, the blades for a 16fthollow-steel airscrew cost eight times as much as equivalent light-alloy blades. ENGINE AND FUEL ACCESSORIES de Havilland Engine Co. One ofthose annoying new developments which can be displayed but not sectioned ordescribed is the peroxide starter devel- oped "for the next generation of largeturbojets" (which, without stretching the imagination unduly, might include theGyron). When brought into contact with a suitable catalyst, concentrated hydro-gen peroxide decomposes to form a jet of superheated steam and free oxygen.In the Super Sprite rocket the jet is used to provide thrust; in the new starterit spins a turbine which is geared to the nose of the turbojet. The photographshows the neat unit under a transparent bullet fairing (p. 496). Dowty Fuel Systems. Continuousdevelopment of the single-circuit type of fuel system, with spill burners, has nowresulted in "systems engineered" instal- lations with a number of good features.From the performance aspect, all-speed governing is provided, with mechanicalcontrol of top-speed, and with mechanical or electric trim for control of maximumtemperature. The characteristics of the spill burner are such that the bulk flowrequires no fine filtration, no filter de- icing and no fuel preheating. The servoflow, on the other hand, has a suffi- ciently small volume (about 30 gal/hr) for Plessey hydraulic power pack. this flow to be filtered without trouble.The two chief exhibits were quarter- longitudinal sections of two turbojets, onewith 16 upstream-injection burners and the other with 10 spill burners injectingdownstream; the former having a twin- pipe gallery and the latter having theconcentric type of gallery with the spill pipe mounted inside the main supplypipe. Both exhibits seemed to represent actual engines which could be seen else-where in the Static Exhibition. The former installation had a maximum flowof 2,100 gal/hr and a total weight of 91 lb, including burners and gallery. Thelatter (a two-spool engine), was designed for a maximum flow of 4,200 gal/hr andit embodied an electric trimming control, incorporating an Ultra electric box toprovide very accurate speed control to within ±5 r.p.m. at 50,000ft and over.The total weight of the installation was 125 1b. Both installations were engineered toincorporate all units in one large cast body mounted under the axial compressorcasing. The geometry of both systems was such that the space envelope of thebasic engine was nowhere exceeded, and particular care was taken to provide easyaccess for maintenance; for example, in- dividual units could be removed withoutdisturbing the remainder of the system. Externally the installations have a verytidy appearance and, owing to the almost complete elimination of external piping,are claimed to be more trouble-free and less vulnerable than previous fuelsystems. Rotax. Ip the field of aircraft startingdevices the principal new development is a monofuel starter using iso-propylnitrate. From the production point of view the company have fortunately beenable to utilise several major components of the original cordite starter; die onlycompletely new equipment being the combustion chamber and turbo-pump. Although no cartridge is employed, thecompany have been able greatly to reduce the battery load (compared with the firsttypes of monofuel starter) to less than five amps. Upon depression of thestarter button a sequence switch is energized which permits a small quantityof i.p.n. to enter the combustion chamber under pressure of air from a cylindricalbottle. Fuel is then ignited by a spark and the resultant hot gas used to drivethe starter turbine. A particular feature of the unit is that only a small turningmoment is initially applied as the gas flow builds up, a proportion of the latter beingby-passed to drive the turbo-pump which is used to supply the main flow of fuel.Once the turbo-pump is in action the air bottle is shut off. Although the air bottle is small, itscapacity is sufficient for three starts on a large turbojet. A future system may
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