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Aviation History
1949
1949 - 1361.PDF
AUGUST 4TH, 1949 FLIGHT 125 F-94, as briefly noted on page 8 of our July 7th issue, is a radar-equipped variant of the TF-80C two-seater jet trainer. Its mission will be high-altitude interception of enemy attack, especially under conditions of bad weather and visibility that would ground the ordinary jet fighter. The installation of modern radar equipment and a radar operator enable this new type of U.S.A.F. fighter to operate all round the clock, day or night in foul weather or fine. Basically, the F-94 is really a structural derivative of the F-80 Shooting Star, in so far as the wing, tail, mid-section fuselage and landing gear are concerned; hence its produc- tion will require a minimum amount of new tooling. Since the same major assemblies are used for the F-80, TF-80 and the F-94, Lockheed plan to build them on parallel assembly lines, which obviously leads to considerable economy of time and money. Also, because of the structural and internal affinity, the first F-94 was completed much sooner than the usual minimum design and development period of r8 months for a new jet fighter type. At the moment, Lockheed have no F-94S on order. The most noticeable differences between the F-94 an(l the now familiar F-80 are the bulbous nose and tail extremities of the F-94 fuselage. The nose houses a Hughes airborne radar with 18-inch antenna and an armament installation of four 20-mm cannon, while the tail-pipe is fitted with a Solar after-burner which considerably boosts the normal 4,600 lb static thrust rating of the Allison J-33 turbo-jet. Lockheed after-burner research has shown promise of very substantial thrust augmentation gains amounting to as much as 50 per cent at low speed and 100 per cent at sea-level top speed— which means that the overall thrust of the turbo-ram-jet combination could vary from nearly 7,000 lb at take-off to over 9,000 lb at sea-level top speed. Once the after-burner technique is perfected, it will solve some of the outstanding snags inherent in jet fighter design—particularly the sticky take-off occasioned by the low thrust at low speed. The aforesaid Lockheed design studies have indicated that, whereas the gain in top speed is of the order of 10 per cent, the take-off run to clear 50ft can be halved and the initial rate of climb increased by as much as 200 per cent. At present, these figures are undoubtedly a bit optimistic, since current after-burners are probably delivering about 60-70 per cent of the gains postulated on paper. Because in engineering design we never get something for nothing, these performance gains are obtained at the expense of further mechanical gadgetry—even though the actual weight increase is not alarming—about 20 per cent of the weight of the turbo-jet. There is a relatively small loss in the exhaust gas stream from the turbo-jet when the after-burner is inoperative, due to the obstructive A mythical Northrop Flying Wing with boundary-layer control and powered by two 10,000 h.p. Norihrop turbcdyn? engines. The design looks like a cross-breed between the 6-35 and B-49 bimbers. Note the new type pilots' cockpit with greatly improved view. effect of the burner installation. With careful design, this thrust decrease can be kept down to less than 5 per cent. One more item of gadgetry is the necessity of a variable- area exit nozzle to the tail-pipe, in order to maintain the same pressures and temperatures in the turbo-jet engine, with or without the burner in operation. The fuel consumption of the after-burner ram-jet is naturally very high, but this is not a serious obstacle, because its use is intended only for short periods when high performance is demanded. Moreover, studies indi- cate that in a climb to, say, 40,000ft, the total amount of fuel consumed by a turbo-jet plus after-burner may be the same or even slightly less than that used by a turbo- jet making the same climb without benefit of such an extra —due, of course, to the time differential in the respective climbing rates. Whilst most of the recent progress in after-burner design and flight development appears to be taking place in the U.S.A., it might be recalled that this form of jet power boost was initiated in England as long ago as 1944. Its development was spurred forward under the impetus of London's "V-i" bombardment, as it was thought that later fly-bomb versions would be faster and more diffi- cult to shoot down from pursuing aircraft. Known at that time as '' re-heating,'' a two-seater Meteor with Rolls- Royce Wellands, was modified at the R.A.E. with an after-burner installation, and considerable research data was obtained from flight tests. It is even possible that The Lockheed F-94 all-weather jet fighter developed from the F-80 fighter and TF-BOC trainer. The pilot is seated in front with radar operator behind. Note the bulbous radar nose and enlarged tail pips mounting a Solar after-burner, An Allison J-33 radial-compressor turbojet. normally rated at 4,600 Ib s.t., is fitted.
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