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Aviation History
1960
1960 - 0077.PDF
FLIGHT, 15 January 1960 CONWAY THE EVOLUTION OF THE FIRST ROLLS-ROYCE BY- PASS TURBOJET WITH the Rolls-Royce Dan turboprop Britain won, for thefirst time in history, a substantial slice of the market in air-line powerplants. This was achieved not by any intrinsic efficiency of the Dan so much as by the fact that it worked reliablyand was available at a time when few of its competitors could do either (and none both). In contrast, the Rolls-Royce Conwayby-pass turbojet has from the outset had to contend with keen competition from engines which in most respects are quitecomparable. With the advent of the American "Big Jets" a situation hasarisen in which the world's airlines can choose either American or British powerplants for the most expensive equipment everoffered to them. That in many cases the Conway has been chosen can be attributed clearly to the fact that it is technically superiorto any alternative engine. This is not an idle claim: Rolls-Royce can point directly to greater thrust, lighter installed weight, lowerspecific fuel consumption and greater promise for the future. As a result the Conway bids fair to becoming the finest transportpowerplant for the largest airliners throughout the Western world. But it is also an engine of extraordinary technical interest, and itis fortunate that permission to describe the present airline version has come when a Conway-powered aeroplane is being deliveredto our global flag-carrier (see the two preceding pages). As we have already outlined (notably in our issues of February 8,1957 and October 30, 1959), the overall efficiency of an aero engine is the product of its thermal efficiency and Froude propul-sive efficiency. What is ideally required is an engine which operates at the highest possible peak temperature and pressureratio, yet which imparts a low acceleration to the largest possible airflow in order to minimize the jet velocity. To achieve this goal,the by-pass turbojet employs an oversized low-pressure com- pressor, the delivery from which is split into two distinct streams.The innermost core is further compressed in a high-pressure compressor and passed through the combustion chambers andturbine. The outer pan of the delivery is discharged through a duct surrounding the rest of the engine and is finally mixed withthe hot central jet in the propulsive nozzle. Compared with a simple turbojet of the same thrust such an engine handles a larger airflow, and the lower mean jet velocityreduces the noise energy by a very wide margin. Moreover, since all components behind the low-pressure compressor can be sub-stantially reduced in size, the engine can be made significantly lighter than the simple turbojet. Again, although the maximumflame temperature can be raised to the highest level consistent with good turbine hie, the adverse effect which this has on jetvelocity (from the viewpoints of Froude efficiency and noise) can be overcome by the injection of by-pass air. As a result, an enginewith a carefully chosen by-pass ratio can beat any simple turbojet of the same thrust when the two engines are installed in similaraircraft and assessed on a basis of air-miles per pound of fuel. It is recalled that Sir Frank Whittle conceived and patented thebasic thermodynamic principle of the by-pass engine, and patents were assigned to Power Jets (R & D) Ltd, the Government-ownedcompany which holds all Sir Frank Whittle's patents relating to aircraft gas turbines. Nevertheless, it remained for Rolls-Royce to design and developthe Conway—the first, and so far the only, large by-pass engine in the world. Like most of the powerplants conceived at Derby, thebasic Conway has already evolved into a complete family, current members of which give exactly double the thrust of the firstprototype. Just ten years after Sir Frank's original patent, Dr A. A.Griffith, the chief scientist of Rolls-Royce, sketched a by-pass engine built up from parts of the AJ.65 (Avon) and AJ.25 (Tweed).In April 1947 a revised version was studied, rated at rather less than 5,0001b thrust, and further projects appeared in October 1947and April 1948. In October of the latter year Rolls-Royce decided to submit a by-pass engine to meet a Ministry of Supply require-ment for a powerplant for the Vickers-Armstrongs Pathfinder (a special development of the Valiant for which the black-paintedB.2 served as the prototype). Initially designated RB.80, its design thrust was 9,2501b. Considerable further development tookplace upon this basic design, and finally a prototype was manu- factured in January 1950 as the Conway RCo.2. During the development of the RCo.2 it became apparent that continued on page 80, after double-page drawings of Conway) Engine type Configuration and design changes. Basic weight (Ib) Performance: A. Guaranteed mini- mum thrust (Ib) B, Average achieved thrust (Ib) C, S.f.c. (average) D, S.f.c. (cruise) History: First bench run First 25hr test First 150hr test First type-test Total bench time No of dev't engines Production delivery First flight Flight time Applications RCo.2 First R-R by-pass engine. Two-shaft engine, with 4- stage l-p. com- pressor, 8-stage h-p compressor, 2-stage h-p. tur- bine and 2-stage l-p. turbine. 3,385 9,250 0.67 August 1952 April 1953 Not run Not run 133hr 52min 1 Not produced Not flown Nil Vickers Pathfinder RCo.5 Redesigned to ligher mass flow and p ressu re ratio. New 6- stage l-p. com- pressor, 9-stage h-p. compressor, single - stage h-p. turbine and origi- nal l-p. turbine. 3.473 13,000 0.735 July 1953 January 1954 December 1954 July 1955 3,064h- 13 Not produced October 1955 980 V.1000 RCo.8 Conversion of RCo.5 with im- provedair-cooling system to permit operation at in- creased flame temperature. 3.500 14.500 0.75 January 1956 January 1956 May 1956 Not required 2,312hr 9 (RCo.5 converted) Not produced Jan. 1957 (Ashton) 2 Victor B.2 RCa.10-12 New design, with zero-stage on t-p. compressor, new h-p. compressor and new l-p. tur- bine. Completely new exterior suited to nacelle installation. RCo. 12 (uprated) suc- ceeds defunct RCo. 10 rating. 4,542 17,500) 9,980* 18.000 i 0.725 0.874 November 1957 March 1958 June 1958 June 1958 16.000hr September 1958 October 1958 DC-8 707-420 RCo.11 Closely related to RCo.10/12. Tai- lored to wing in- stallation, acces- sories not being mounted on en- gine but on air- frame. Restricted 17,250 Restricted Victor B.2 RCo.15 Increased dia- meter zero-stage on l-p. compres- sor, and improved h-p. compressor with higher efficiency. 4,582 18.500, 9,895* 19,000) 0.701 0.842 January 1959 January 1959 July 1959 Early 1961 1960 DC-8 (CPAL) -l»v«l static ISA standard day; performance D is 47Skt at 36,000ft; asterisked figures are high-pressure J RCo.42 Extensive revision to increase C/H ratio to 0.6. A com- pletely new Up. compressor inc- reases overall dia- meter to 45in, and numerous other changes have been made. 5,001 20,2501 9,955* 21,0001 0.622 0.785 Early 1962 VC10 707-520 r.p.m.
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