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Aviation History
1959
1959 - 1746.PDF
FLIGHT, 19 June 1959 : 831 ::A' 1,720-knot Airliner STRIKING PROPOSAL BY BRISTOL SIDDELEY DURING the past three months many have expressed theview that the recommendations to the Ministry of Supplyby the Supersonic Transport Aircraft Committee are, to say the least, modest. Such an adjective could not be applied toa transport project described in a paper entitled Power for the Long-range Supersonic Airliner by R. R. Jamison, assistant chiefengineer of Bristol Siddeley Engines. That the engineers at Filton have been striving to apply the ramjet to manned aircraft has longbeen known, but this is the first occasion on which tangible details of such a scheme have become available for publication. In bis introduction Mr. Jamison stressed the relationshipbetween speed and range in "main-line" transport aircraft; both qualities were demanded and the first was difficult to exploit with-out the second. Current jet liners already, flew as fast as possible without incurring the severe drag penalties associated with tran-sonic flight with conventional airframes. In effect, designers were up against what was virtually a discontinuity in aerodynamics. Thelecturer proposed to examine a range of cruising speeds from M 0.8 upwards to an indefinite limit. Air stagnation temperatureat M 3 in the stratosphere was about 600 deg K and at M 4.5 about 1,050 deg K, so that the latter appeared a reasonable upper limitfor the study. After bringing together the desirable properties of payload,range and speed in the familiar Breguet formula, Mr. Jamison rewrote this in a revised form in which range was expressed interms of the calorific value of the fuel, lift/drag ratio, ratio of air- craft weights at the start and end of cruise and a factor representingoverall propulsive efficiency (namely, work done against drag divided by fuel heat input). The latter term became supremelyimportant and, notwithstanding the drastic fall in L/D from about 18 at M 0.8 to about 8 or less beyond M 1.2, the great improvementin propulsive efficiency more than restored the balance, provided one could fly fast enough. Overall efficiency of a turbojet at M 1did not exceed 18 per cent, but the corresponding value for a ram- jet at M 3.5 might be as high as 55 per cent.As a result it was possible to draw Fig. 1, from which it could be seen that, provided there was no serious rise in structure weight,one might restore the full range performance of the high-subsonic aircraft between M 3 and 3.5. This curve also emphasized that theramjet, which had a superior performance to the turbojet above M 3, deserved serious consideration as a component of thepowerplant. One could exploit the potentialities of the ramjet by building anall-ramjet transport, associated with a launcher component capable of starting from rest; in the present study, however, it had beenassumed that an aircraft was required which could operate in a normal manner from existing airfields, with full civil safety stan-dards. This implied that, if ramjets were to be used, they must be applied in combination with enough turbojets to satisfy existingoperating standards. The lecturer termed such an arrangement a combination engine; it could be made up in various configurationsaccording to the areas of intake duct required for each component. Although they might be considered modest values, Mr. Jamisonsuggested turbine entry temperatures of 1,200 deg K for cruise and 1,250 deg K for take-off. Anything hotter might involve exces-sive noise, intensified cooling problems and other undesirable factors. Compared with subsonic aircraft the projected machine wouldhave relatively large powerplant airflow. This is derived partly from the greatly increased cruise thrust per pound of aircraft weight ren-dered necessary by the fall in L/D, and from the fact that the best overall propulsive efficiency was realized at low jet temperatures(and hence low specific thrust). Overall duct areas thus became three or four times as great as those in subsonic jets, and this Fig. 7 (below). A typical curve of range factor for air- breathing aircraft, showing the improvement at high Mach numbers resulting from the increased propulsive efficiency Fig. 2 (right). End, side and plan views of the complete combination turbojet/ramjet propulsion system. It is shown in a perspective cutaway drawing on the next page 2 VARIABLE AIR INTAKE COMMON TO RAMJET AND CAS TURBINES "O r TRANSITION SECTIONCIRCULAR TO RECTANGULAR DESIGN POINT z n 2 8 d • <*> CM A o <E §> £ UJO z o / / / SECTION THROUGH TURBOJET BAY SUBSONIC POSITION OF RESTRICTOR DESIGN POINT SECTION THROUGH RAMJET BAY DESIGN POINT < ~n 2 3 MACH No COMMON AIR INTAKE DUCT PLAN VIEW
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