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Aviation History
1955
1955 - 1437.PDF
30 September 1955 Two views of RJTV 27, the obviously unused ramjet test-vehicle which was publicly exhibited at the N.G.T.E. last week. Many transmitting aerials (whip aerials) protected from its silver skin. Curiously, the vehicle has no ventral fin, no doubt to ease launching problems. RJTV 27 A British Ramjet Development Revealed SO far, very little has been revealed regarding British workin the field of ramjets. In fact, the only tangible evidenceof progress was the static display (at the S.B.A.C. exhibi- bition of 1952) by the Bristol Aeroplane Company of a twin-ramjet, rocket-boosted test vehicle, which we illustrated and discussed at that time. Last week, the Ministry of Supply permitted a visit to theNational Gas Turbine Establishment at Pyestock (South Farn- borough), Hants. Notwithstanding its tide, this establishmentis also considerably concerned with ramjets. As far as non-helicopter applications are concerned, the ramjetis a supersonic engine. Compression of the intake air is effected by the conversion of energy from kinetic to pressure; and thisprocess is largely governed by die shock-wave pattern at the intake. Simplest of all intakes is the direct pitot (a simple hole)but the normal shock produced by such a system causes severe losses in efficiency at high supersonic Mach numbers. Muchbetter pressure recovery can be had from the family of inclined shocks arising from a spiked centre-body. At Mach 1 a pres-sure ratio of about 1.8:1 can be obtained, but this improves to no less than 36:1 at Mach 3 (say, 2,000 m.p.h. at high altitude). Fuel is injected aft of a diffuser section, and the resulting jetof hot gas (it is virtually a continuous flame) escapes from the propelling nozzle at the rear. The only rotating componentneeded is the fuel pump, and this can readily be driven by a ram-air turbine. An obvious penalty of a ramjet vehicle is, ofcourse, that it is not self-sustaining until it has reached a quite considerable flight speed (about M = 1.5 for a M = 2 vehicle). Another difficulty in ramjet testing is the scale of test equip-ment needed. By its nature, a ramjet has either to be pushed through the air very quickly (much faster than any presentBritish aircraft) or else have to have a simulated supersonic airflow fed into it. In practice both methods are used, theground running being used up to the limits of its capability— which are usually far short of the design speeds and altitudes.Ground rig-testing is, however, a pre-requisite to any free-flight trials. At the N.G.T.E., combustion chambers for ramjets are bolteddirect on to the end of die plant air-supply. The latter is fed in at from 40 to 50 lb/sq in absolute (corresponding to supersonicflight at fairly low altitude) thus imposing mechanical loading comparable with those of the worst flight conditions. In addi-tion, powerful hydraulic jacks are used to move the air valves in order to reproduce the violent build-up of both airflow and pressure experienced during a rocket-boosted take-off of a testvehicle. To test the combustion at high altitude (where problems areusually worse) it is necessary to employ a continuously exhausted chamber where ambient pressure is considerably below atmos-pheric. At the N.G.T.E. a relatively small chamber was shown, in which models could be tested at up to M = 2 at 40,000ftequivalent altitude and at angles of attack (or yaw) of up to 15 deg. Shock formation could be recorded by means of sparkphotography. Ultimately, of course, there is no substitute for full-scale free-flight trials. The principal method of conducting such trials has been to build the ramjet into a simple fuselage, complete withstabilizing fins, and launch it by booster rockets capable of impart- ing so high an acceleration that the ramjet reaches its criticallight-up (self-sustaining) speed before the boosters burn out. One such test vehicle was actually on view, and is illustrated here. It was designated RJTV 27 (ramjet test vehicle), and had beenbuilt by D. Napier and Son, Ltd. At a rough guess the length and diameter must be about 16ft and 20in, respectively, and theweight (less boosters) about 1,000 lb. No information regarding this fearsome vehicle was forthcoming, but it is unlikely to havebeen designed for a Mach number higher than about 1.5, owing to its use of a plain pitot intake. This intake is bifurcated into upper and lower ducts, and itis believed that fuel is contained in a flat tank between the upper and lower airflows. Above and below the centre sectioncould be seen small intakes (visible in the photograph) which admit ram air to the fuel pump; the corresponding exhaust ison the port side. At the forward end could be seen transmitting aerials for the information required by the ground station, oneunit on each side of the fore-body being a curious Perspex prism mounted over a piece of embossed foil—presumably a trans-ponder for radar tracking. Doppler speed transmission is probable.There are eight boosters, each pair carrying a massive fin and joined together at the front by a small wing (set at about20 deg) used to pull the boosters away at the separation point. All fins are of trapezoidal section. Altogether, it was instructive and heartening to see RJTV 27,particularly as it is fair to assume that it must now be outmoded by much later vehicles. Most such test-vehicles are, of course,completely expendable, although it is likely that a great deal of useful information can result from examination of the wreckage.
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