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Aviation History
1961
1961 - 0657.PDF
FU IT, 18 Afav 1961 667 SIX DERBY WINNERS Rolls-Royce Aero Gas Turbines BY THE TECHNICAL EDITOR Spey I running in ten cell ON August 17, 1956, this journal published a review of Rolls-Royce commercial gas turbines, under the title "Four DerbyWinners." These four engines were the Avon, Conway, Dart and Tyne, and a lot of water has flowed under the bridges acrossthese rivers since that account was written. Of the 48,000 Rolls- Royce employees, 38,000 work on aero engines, and 8,500 of theseare design and development engineers whose output is not incon- siderable. The author feels, therefore, that if the Rolls-Royceengine picture is ever again to be examined as a single canvas, the time is now; for every week brings new problems, new experienceand new accomplishments. AVON No aircraft engine has a more extensive background ofoperating experience than the Rolls-Royce Avon turbojet. Develop- ment of the original AJ.65 started in 1947, leading to the Avon 100described in Flight on December 16, 1955. In 1951 the much more advanced Avon 200 series was produced, described in Flight forOctober 11, 1957. Today, well over 3,000,000hr has been flown by military engines, and flight-time on the commercial Avons isapproximately l,000,000hr. It is appropriate to discuss the two families separately. Commercial The original airline Avon was the RA.29, whichdiffered from earlier versions principally in having a zero com- pressor stage (making 16 stages in all) and a third turbine stage.The first engines built to the Stage I (RA.29/1) standard were the Mk 522 (take-off thrust, 10,5001b)* for the Caravelle 1. and the 524,525 and 525B (10,2501b) for the Comet 4, 4B and 4C. The Comet engines, many of which incorporate reversers, have now flown700,000hr in scheduled operation. The Mk 524 engines in BOAC Comet 4s are at present cleared for 2,600hr between overhauls, and2,9OOhr will be approved when a sufficient number of engines have been inspected at that figure. No other turbojet has yet exceededl,600hr. Further development of the commercial Avon has been directedtowards the achievement of increased power for the Caravelle. The Stage III rating (Mk 527, 11,4001b) was established merely byimproving the turbine-blade material and fitting a two-position nozzle. The nozzle area is varied by a flap hinged between two ofthe silencing lobes, and the nozzle is usually fully open except at take-off. The Mk 527 went into production for the Caravelle 3 inJanuary 1960, and earlier Caravelle engines have been brought up to this standard at overhaul. Much the largest advance in the development of the commercialAvon occurred when a "zero-zero" stage was added at the front of All ratings are minimum guaranteed. the compressor, to produce the Stage VI engine for the Caravelle 6.The basic Stige VI is the Avon 531 (12,2001b), in which flame tem- peratures remain approximately at the level of the Mk 527. and anumber of refinements combine with the increased pressure ratio to reduce the specific consumption. This engine entered scheduledservice on February 18, 1961, with Sabena. The Avon 532R (R for "reverser") incorporates improved material and cooling arrange-ments in the first turbine stage in order to operate at higher tem- perature (12,6001b). Fitted with a modified fuel system, incorporat-ing a separate shut-off cock, the engine is fitted to the 20 Caravelle 6Rs bought by United. The FAA will start these engines off at anoverhaul life of l,200hr. Military Supplementing the many thousands of military Avon100 and 200s is a new family with mark numbers starting at 300. These engines are at present more widely known by their experi-mental nomenclature of RB. 146, and are essentially a cross between the RA.24 and the commercial RA.29. The RA.24 is in large-scaleuse with the RAF and Royal Navy, both with and without reheat, and has a higher flame temperature and air-cooled turbine blading.To produce the RB. 146 Rolls-Royce added the civil engine's zero- stage, but retained the original two-stage turbine (although with alow-pressure wheel of increased diameter). Aluminium alloy is used for the first five compressor stages, the remainder being steel ortitanium. During the past ten years Rolls-Royce have developed a series ofreheat jetpipes (afterburners) of steadily increasing capability. As flight Mach number increases, the optimum propelling-nozzlediameter does likewise. Most of the early reheat nozzles had a diameter of 2ft, and even in the Swift and Lightning installationallimitations hold it to some 28in. On the other hand, the Mirage and Draken impose no restriction in this regard, and first-classinstallations are flying in both. For the former aircraft, Dassault and Rolls-Royce reached ajoint agreement last year to offer an RB.146-powered version for export and to effect a one-off trial installation. Designated MirageIIIO, this aircraft has an airframe made available by the French Air Ministry and an engine belonging to the British Ministry ofAviation and designated Avon Mk 67. The Rolls-Royce reheat system is served by an air-turbine fuel pump and has a fully variablenozzle with roughly twice the area of previous patterns. The nozzle has 16 hinged fingers, alternate fingers being drivsn on rollersalong curved tracks under the thrust of eight ball-screwjacks engaging in an annular gear-ring coupled to a Plessey air motor.The aircraft first flew on February 13. It has already conducted extensive trials with operational loads (picture, April 20, page 525),has a markedly improved performance compared with the standard Mirage, and may well be the fastest aeroplane in Europe (includingBritain). It has been flown by French, Australian and other pilots, and has been notably free from any major powerplant trouble. Avon RA.2911
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