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Aviation History
1957
1957 - 0574.PDF
The Jet Gyrodyne which proved the operating technique and method of conversion front helicopter to autorotative flight for the Rotodyne. ROTODYNE PRELUDE .... times that of the average turbojet, since much richer mixturesare used. Efflux temperatures of 2,000 deg C are obtained, and thrusts of about 1,200 lb per Rotodyne unit are expected. Themass flow through a Ghost chamber is about the same as that through the Rotodyne pressure-jet, but the heat release of thelatter is about four times greater. The total fuel consumption of the complete Rotodyne rotor at take-off will be about 1,000gal/hr compared to about 750 gal/hr for a complete Ghost. This is not exorbitant, because the Rotodyne pressure-jets would beused only during take-off and landing. During these phases, rotor r.p.m. would be held substantially constant at about 153r.p.m. During cruising at 135 kt, with the rotor partly unloaded, the r.p.m. would drop to about 130 and the tip jets would not bein use. Faireys estimate an initial tip-jet unit life of about 50 hours, increasing to between 200 and 300 hours at a later date. Since only10 per cent of total flight time is envisaged for tip-jet propulsion, the installed life of each pressure-jet will be about 10 times theactual operating life of the tip jet unit. One of the great achievements of the Fairey team is the success-ful design of suitable pressure-jet liners. In this they are well ahead of other companies. Another successful development inthe field is the effective tip-jet lighting mechanism which, based on a Napier-developed two-Joule 500 V, fast-sparking ignitionsystem, can light the tip jet during mass flows very considerably higher than any which have been attempted for the re-lighting ofturbojets. The design of this special llghting-up system in fact exercised the Fairey design team quite considerably in the pre-paration of both Gyrodyne and Rotodyne systems. Whereas in the Gyrodyne the ignition system is operative throughout the useof the tip jets, only a 20-second ignition burst is used for the Rotodyne units; at full air supply, light-up is almost immediate. The Rotodyne propulsion system is, of course, based on twoNapier Elands arranged to drive either a propulsive airscrew at the forward end of the engine or, through a clutch, a ten-stageaxial air compressor located aft of the bifurcated engine efflux. For the take-off phase, the power of the Elands is devoted to driv-ing the compressors so that these supply air to the tip-jet units. A flow of fuel to these units is regulated and, after being atomizedin the flame tube, is ignited to provide thrust for the otherwise free-wheeling rotor. Full helicopter-type rotor control is usedin the helicopter flying phase at take-off, hovering and landing. The initial rate of climb in this condition is estimated at somel,500ft/min. At a suitable time the power of the Elands is pro- gressively diverted to the propulsive airscrews, the tip jets beingphased-out at the same time so that, when conversion is complete, total propulsive effort is derived from the Bland airscrews and liftis shared by the partially unloaded rotor and the Rotodyne's short wings. Flight control is then achieved with the assistance ofaerodynamic control surfaces on the tail and wings. It is to test this complete power system that the very large rigat Boscombe Down has been set up. There, the actual rotor head of the first Rotodyne is mounted on a large steel structure, togetherwith the wing and Eland power units, all set in their correct dimensional relationship to each other. A cockpit unit containingtest instrumentation and the actual pilot's control position is housed in a small wooden shed, again set in dimensionally accuraterelationship to the rest of die system. At the moment, one Eland and two of the four rotor blades are being used. The power of the rotor with tip-jets on is regulated either bychanging the power input into the compressor section (in the case of the Ultra-Light) or by movements of the air-supply valve (inthe Jet Gyrodyne and Rotodyne). Both types of control are con- nected to the collective-pitch lever with an override control in theform of a twist-grip on top of this lever. Fuel is supplied to the tip jets by a low-pressure pump which raises it from the tank to 576 FLIGHT, 3 May 1957 the rotor head, whereupon centrifugal force builds up a pressureas high as 1,000 lb/sq in at the burners. Fuel supply and air/fuel ratio are automatically adjusted by a special regulator unit. A most important programme, begun by Faireys in 1952, hasbeen that of suppressing the noise of the tip jets. A great number of differently-shaped orifices for these units has been tried, withthe result that noise attenuation of some ten decibels has now been achieved for a thrust loss of only five per cent. This thrustloss could be restored by injecting extra fuel for only an insignifi- cant increase in noise level. Though such a power loss would beserious for a turbojet system, it is not critical for the short operat- ing periods envisaged for the Rotodyne. The noise of the Roto-dyne tip-jet units has now been reduced from 105 db to about 95 db. Below this point further reduction does not offer greatadvantages, since the rotor noise itself is of about this value. The radial flame-tube of the pressure jet used in the Fairey Ultra- Light helicopter. The unit is shaped to fit inside the blade profile, and special liners and fuel spray had to be developed for it. Extensive measurements have been made and it is hoped thatthe noise of the Rotodyne at take-off can be reduced to a level comparable with that of a tube train. The high rate of climbon take-off will further help to reduce noise nuisance. Experiments have now shown clearly the requirements forsilencers for this kind of application, and further work is in hand to increase performance. It has been found that the best silencingcharacteristics can be achieved by channelling the efflux flow through a series of slots spaced as far from each other as possible.Optimum slot-widths have been arrived at, and the configuration of the latest silencer is a sixteen-pointed star formation of radialslots. The efflux area is substantially the same as that of the original circular nozzle and the area of the whole silencer is there-fore rather larger than that of the old nozzle. Subsequent develop- ment is aimed at reducing the resulting drag still further. To carry out all this work, Fairey have to a certain extent madeuse of the facilities of the National Gas Turbine Establishment at Pyestock, but they have also developed considerable new instru-mentation for such purposes as that of measuring the thrust of a pressure jet while it is rotating at the end of a blade.By the time the Rotodyne flies it will have behind it some ten years of intensive pressure-jet development and much practical ex-perience of operating technique. HAWKER SIDDELEY AND BRUSH /COMMENTING recently on the proposed Brush - Hawker^ Siddeley merger [mentioned in a news-item on p. 534 of Flight last week] the chairman of the Brush group, Mr. Geoffrey Eley,said he had been aware ever since he joined the Board three years ago of restraints imposed on the group's growth by under-capitalization. The Hawker Siddeley group would provide the financial backing required for expansion in the field of nuclearpower, and it was fortuitous that their ideas and those of Brush in that field were "very much alike". Adding that HawkerSiddeley's "commanding position in Canada" held "great interest" for the Brush group, Mr. Eley said the Hawker Siddeley offer was"the best possible proposal" for the Brush Group. In his comments on the proposed merger [as briefly reportedlast week] Sir Roy Dobson, Hawker Siddeley director, said: "We feel that the Brush group offers us an exceptional opportunity tolink our world-wide facilities with theirs, to provide Brush with the financial resources required for their development programmeand ... to give our stockholders and theirs a really good deal. "We are vitally concerned in the development of nuclear energyand the means of distributing power from it. By merging our technical and financial resources with Brush we can take a furtherbig step that will be all-important in the years to come."
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