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Aviation History
1956
1956 - 1106.PDF
252 FOUR DERBY WINNERS FLIGHT time amounts to over 40 hr in the air and more than 1,000 onthe bench. Next summer Rolls-Royce will install two Tynes in an Elizabethan borrowed from B.E.A. for endurance flying. Inview of the success of the Dart-Dakota used on scheduled B.E.A. freight services, it is probable that similar operations will becarried out with rhe Tyne-Elizabethan. The official type test is scheduled for September-October 1957 and the prototypeVanguard is due to fly in September 1958. The Lockheed Air- craft Corporation are also considering the purchase of Tyneengines for evaluation as an alternative powerplant for the Electra. This type of Tyne is due to be type-tested in November1958 and certificated engines ready for Lockheed early in 1959. Vanguard-engine development is outlined in an accompany-ing table. Recently a minor redesign was incorporated in the compressor to give powers which exceed those so far publishedand lender all the tabulated figures pessimistic. Within limits it should be possible to select any low-pressure cruise r.p.m. togive the required balance of fuel consumption, airspeed and noise level. In B.E.A. service it is probable mat the latter factor willbe predominant and it is unlikely that the low-pressure setting will exceed 12,500 r.p.m.; in North America no doubt Tyne-powered aircraft would be cruised as fast as the requirements of economic overhaul life would allow. On the Vanguard thereduction gear ratio is 0.064, the airscrew being a de Havilland fcur-blade unit of 14ft 6in diameter. Operations with British European Airways are due to startearly in 1960, by which time engine flight-hours on the Tyne- Elizabethan, supported by the first V.951s, should be about10,000. It is expected that initial certification by both the A.R.B. and C.A.A. will be on a basis of 400 or 500 hr. The Tyne 506"Stage 1" engine should reach the fully-fledged, 1,000-hr basis by the middle of 1961. At this time the "Stage 2" engine is due tobe introduced to service, with a higher top temperature as a result of improved turbine-disc cooling and a new blade material. Twoyears later the "Stage 3" Tyne is scheduled to go on to the routes. This engine is at present the ultimate version for which a firmprogramme is being quoted; like the later Darts it will feature improved blade cooling in the high-pressure turbine stage. Table 3: Performance of Tyne engines in Vanguard aircraft Engine data: Diameter, 40.Sin, length, 100.25in; weight, 2,023 Ib; pressure ratio, 13:1.Take-off, s.l. static, i.s.a., 15,250 r.p.m.: Stage I (1959),4,695 e.h.p. (4,220 b.h.p.): Stage II (1961). better than 5.075 e.h.p.; Stage III (1963), better than 5,500 e.h.p.Maximum recommended cruise, 25,000ft, 370 knots, all figures (power and S.f.c.) will be from three to five per cent better than: Stage I, 2,700 e.h.p. at14,000 r.p.m. at 0.412 Ib/hr/e.h.p.; 2,640e.h.p. at 13,500 r.p.m. at 0.411 Ib/hr/e.h.p.; 2.550 e.h.p. at 13,000 r.p.m. at 0.413 Ib/hr/e.h.p.; Stage II, 2,990, 2,920 and2,820 e.h.p. at same r.p.m. with specifics of 0.398, 0.398 and 0.400; Stage III, 3,090, 3,030 and 2,940 e.h.p. at tatr.e r.p.m. with specifics of 0.399, 0.398 and 0.398. Avon Turbojet. As a military engine the Avon is as experi-enced as any unit in the world. It has now been widely employed for six years in bombers, fighters, trainers and transports andenjoys an enviable reputation for reliability. The first family of Avons is based on the Series-100 engine, with a 12-stage com-pressor, eight separate combustion chambers and a two-stage turbine. These engines were fully described and illustrated inour issue of December 16, 1955. The much more advanced 200- series Avon may not yet be described in detail. Development of commercial Avons began in 1950 when thede Havilland Aircraft Company decided that, in view of the weight growth of the Comet, it would be desirable to turn toan engine basically more powerful and efficient than the centri- fugal Ghost. Rolls-Royce accordingly prepared variants of theAvon 100 family designated Avon 500-503, and these were used in the Comet 2 at ratings of between 7,150 and 7,350 lb. Thiswork served to sort out most of the basic airline maintenance problems associated with such an engine. Present R.A.F. CometC.2s and T.2s have a military counterpart of these engines designated Avon 117-118. As an indication of their quality, it isnow over two years since Canberra engines (which are generally similar) were first run to an achieved life of 800 hr betweenoverhauls. During many hundreds of thousands of hours of Canberra flying it has been shown that the incidence ofunscheduled engine-changes is below 0.3 per 1,000 hr flying, even on rugged military training schedules. From the airline viewpoint, interest centres on the 200-seriescommercial unit of the RA.29 rating, in which every good quality seems to be blended in a remarkable manner The latest militaryAvons are now giving thrusts substantially greater than any so far announced, largely as a result of progressive increases in theturbine-inlet temperature. It is on these engines that the bulk of the 6,000 + hours on air-cooled turbine blades has been gained. Running at such fearsome temperatures inevitably raises thespecific fuel consumption and the RA.29 follows the opposite line of development. The thrust requirements vary with theairframe application but, in most aircraft with which it is asso- A five-figure-thrust Avon being withdrawn from the de Havilland Comet 3; the production RA.29 will appear somewhat different. ciated, the RA.29 can eas.ly meet all requirements at almostunbelievably low turbine-inlet temperatures. A further factor is that maximum thrust (10,500 lb dry at 8,000 r.p.m.) is requiredonly while the wheels are on the ground during take-off; during all the rest of each flight—in the Comet 4 at least—the cruisingr.p.m. of 7,150 represents an unusually low proportion of the maximum thrust. Details of the RA.29 are withheld but it can be stated toincorporate a revised design of compressor extended at the front to increase the mass flow and pressure ratio and requiring a thirdstage to be added to the turbine. The engine is a straightforward derivative of the latest military units according to the philosophyof operation at exceedingly low gas temperature. For this reason there is no doubt that it should be quite possible to achieveremarkable component lives and the expected overhaul life on the complete powerplant should fairly rapidly approach 2,000 hr. A few weeks ago a complete type-test schedule was run on anRA.29 with performance almost identical with that predicted. The first public appearance of the engine is expected to be atthis year's S.B.A.C. Show, when one will be flown in a special Canberra test bed. Similar units are also to be installed in theoutboard positions on a pair of Comet 2s; redesignated Comet 2E these aircraft will be used by B.O.A.C. for route proving, endur-ance and general development. The programme is intended to establish, in terms of demonstrated performance, a minimumA.R.B.-approved life of 500 hr by mid-1959 and the company are certain that the RA.29 will then already be a 1,000-hr enginesubject to demonstration of ability. B.O.A.C. and Capital Air- lines are scheduled to put the Comet 4 on to the routes in thewinter of 1958-1959, by which time the RA.29 should have logged over 10,000 hr flying and military Avons more than 3,000,000 hr.Present orders for Comets require the delivery of approximately 200 Avons, to which can be added more than 30 for Air FranceCaravelles. In the present state of the market it is unwise to suggest how these numbers might increase in the coming months.Rolls-Royce are also in an excellent position for supplying com- mercial Avons as a ready and available turbojet for such aircraft asthe Douglas Model 1925 (DC-9). During the next six months it is quite likely that the whole medium-range jet market maybreak wide open and, if the RA.29's leading position is confirmed by selection for American airframes, the volume of business thatcould result is tremendous by any standard. Naturally enough Rolls-Royce are not anxious to give details of what form of enginethey have in mind for the DC-9, but it can be said that investiga- tions are proceeding upon lightened versions of the RA.29 forsuch applications. This is quite practicable owing to the low ratings required and the easy, cool operating conditions. A firm Rolls-Royce philosophy employed in the RA.29 is thatall cabin pressure air is tapped directly from the main engine compressor. This practice has been amply justified by past experi-ence and the unlikelihood of contamination by synthetic oil is shown by the almost insignificant oil consumption of about 0.07pints per hour per engine (the Viscount V.700, incidentally, used a total of a quart of oil during its entire flying time on the NewZealand race three years ago). The lubrication system is an integral part of the Avon. The inbuilt capacity is 15 pints andthe oil cooler is fuel-cooled (requiring no intake and thus giving rise to no drag). Standard equipment includes electric starting,high-energy ignition, automatic synchronization and a power take- off for an accessory gear box. Although they have kept quiet aboutit, Rolls-Royce are also in a leading position in the development of thrust-reverse units for commercial and military aircraft. These,together with various forms of quiet-running (Greatrex) nozzle, are being actively developed. In the latter work the company areexchanging ideas with several airframe manufacturers, including Boeing and Douglas. Conway By-Pass Engine. It is remarkable that, at the presenttime, the Conway is the only example of a type of engine which has long been known and which offers a most interesting com-promise between the conflicting factors which make for propul- .
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