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Aviation History
1961
1961 - 0787.PDF
fLIGHT, $ June 1961 797 Caravel le a la General Electric BY ROBERT D. ARCHER, ARAeS IT was one of those windy spring days typical of Edwards AirForce Base, California. There was very little test flying takingplace as I walked around the Caravelle belonging to General Electric, my interest being concentrated on the two large "barrels"which had sprouted forth at the rear end of the engine pods. As I looked up from the rear I noticed the aft-fans rotating briskly, butthere was no noise other than that from the wind. The Caravelle has proved to be of outstanding interest in thehighly competitive American domestic civil transport field, not the least for being the first foreign design to be sold by the DouglasAircraft Company. In order to stimulate this interest and to allow investigation of future developments of the basic airframe withtheir own engines, General Electric bought from Sud-Aviation a Mk 3 Caravelle. Under the Douglas insignia it completed anintensive tour last summer after making some 66 demonstration flights in the USA. Thanks to the co-operation of both Douglas and GeneralElectric, 1 was able to sample Santa Maria, as it has been called, both on its last demonstration flight before conversion and duringits first Press flight after being fitted with the 16,1001b-thrust General Electric CJ-8O5-23C aft-fan engines. Outwardly the con- version has done little to change the appearance of the aircraft,except for the large-diameter barrel around the aft end of the jet pods. However, General Electric had to make many changes tofit the -23C engine. Because the engine-mounting points are different, the two mounting frames had to be re-located, and insteadof the electric starter system a gas-turbine starter was installed in the rear fuselage tailcone, replacing the previously fitted drag-chutesystem. Extensive recording instrumentation, including a 30-channeltape recording system, has been fitted at the rear end of the pas- senger cabin, and the new engine frames have made it necessary tore-locate the lavatories. The cabin air-conditioning system had to be revised because the bleed air from the seventeenth stage of theGE engine is hotter than that from the lower-pressure Avon. Aircraft conversion was done at Edwards by GE, but the podswere built by Douglas. The engines are almost exactly the same as those fitted to the Convair 990, and are about 80 per cent inter-changeable with those used in the Convair 880—a point which should appeal to the airlines which have purchased these aircraft. There is no doubt that the considerably increased thrust of theaft-fan engines—16,1001b versus the 11,4001b of the previously fitted Rolls-Royce Avons or 12,7251b of the latest Avon—hasconsiderably improved the short-field capabilities of the Caravelle. The production Mk 7 using the aft-fan engine will take advantageof the greater thrust of the engines by providing a 39in fuselage extension forward and a 10,0001b increase in weight over the Mk 3. The aft-fan consists of a single stage of what General Electric call"bluckets"—a corruption of compressor blades and buckets (American terminology for turbine blades). Reverse thrust isprovided by two large clamshell sections similar to those on the CV-990, but opening in the vertical rather than the horizontal plane.The engine uses hot-air de-icing for both the fan and main engine intake. By-pass ratio is 1.56, and the aft-fan operates at a pressureratio of 1.6. Taken for a Ride General Electric chief test pilot R. J. Scoles and Caravelle projectpilot L. V. Davis briefed me on the conversion of the airframe, saying that while the Caravelle's fully powered control system hadno manual reversion and only artificial feel (as opposed to current US practice) in their opinion it was far better than any of thepower-boosted control systems fitted to other civil jets they had flown. Feel for the rudder and elevator is provided by a q-sensersystem and bungees, while the ailerons have torsion-bar feel without q-sensing. Because stability is positive about all the three axes, noartificial stabilization is needed or provided As the engine thrust lines are toed-in by 4° on each side, trim-changes are practicallynegligible in the one-engine-out case. We then boarded the aircraft and I had a quick look at the ratherunpleasant conditions prevailing: there was about a 20kt wind blowing fine sand across the main 15,000ft runway. As we taxiedout I looked around the main cabin, which was unchanged from its original form except for removal of seats at the rear to makeroom for the flight-test instrumentation. The aircraft, No 42 off the production line, was finished throughout and equipped similarlyto those used by SAS. We took off at the maximum gross weight of 101,4001b; on theprevious flight we had weighed 101,2001b. (Figures for the previous Avon-engine flight will be given in parentheses for comparison in Two photographs which highlight the change in appearance of an installa- tion when an aft-fan is added; upper, the Avon 527, with silencer; lower, the CJ-805-23C, with reverser, installed in the same aircraft
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