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Aviation History
1950
1950 - 0975.PDF
relation to the horizontal. FLIGHT, 18 May 1950 AMERICAN NOTEBOOK . . . aviation Press—to start the bidding, as it were. Our own bid, however, based on the 28,000 1b of the Lockheed XF-90, would be considerably higher, say 27,000 lb. With jettisonable wing-tanks a fair certainty for long-range missions, the overload gross weight appears likely to scale the 30,000-lb mark. Following this guestimation process, we arrive at a somewhat breath-taking wing loading of 130 lb/sq ft for a take-off gross weight of 30,000 lb and a net wing area of 230 sq ft. (Admittedly, one can juggle the wing loading down to 105 on the basis of gross wing area, but since the airflow must still get around that bluff, Falstavian body in the middle of the lift mechanism, the air particles are unlikely to be impressed with this kind of book-keeping,) Afterburner boost, plus the usual RATO (rocket-assisted take-off) routine, will come to the rescue for take-off, but the landing speed is bound to be a bit on the stimulating side, for even with the best of long auto- matic leading-edge slats and slotted-type flaps, the maxi- mum lift coefficient is unlikely to be much greater than 2.0, because of the influence of wing obliquity. Thus, even with the landing weight down to, say, 20,000 Ib, the YF-93A will probably touch down at around 130 m.p.h., while in a full-load emergency landing at 30,000 1b it could reach 160 m.p.h. Clearly the RATO routine is due for the reverse technique! A maximum thrust of 8,006 lb has been publicized for the J-48 engine with the afterburner operative. Assuming that this figure refers to the static condition, a sea-level climbing thrust of around 8,500 lb and a top-speed thrust of 10,000 lb appear reasonable values in the light of current afterburner development, based on the installation of a variable-area propulsion nozzle to the tailpipe. Even so, no claim is made by North American that this would enable the production F-93 to push over the transonic hump in level flight, though an operational speed close to the sonic is predicted. The shape of the fuselage-nose entry, for one thing, looks decidedly sub-sonic; while, for another, the low fineness ratio of 6.5 or so is not conducive to low transonic drag coefficients. (In this respect, it is worth noting that its sleeker-looking rival, the Lockheed XF-90, indulges in both these transonic airmarks, for it has a needle-pointed nose and a much higher fineness ratio of about 9.0.) Indulging ourself in, possibly, a rash performance on the shakiest rungs of the Mach ladder beyond M = o.9O, we assess the maximum sea-level speed of the YF-93A at approximately 720 m.p.h. (M = o.g5)—a figure which is based on the aforesaid top-speed thrust of 10,000 lb with the afterburner tap on. At 40,000ft, the corresponding maximum with the afterburner on is estimated at 640 m.p.h. (M = o.g7). The sea-level speed, incidentally, happens to be the same as that predicted for the YF-86D in our Notebook entry of February 2nd, the increased drag of the YF-93A's bigger body just about neutralizing the extra 1,000-lb thrust of the j-48 engine. In view of the high wing-loading.(fluctuating around the century mark at combat gross weights)-, what is not so readily assessable is the handling performance upstairs in Heavyweight fighter. One 01 uie aeparcures noticeable in the YF-93A, as compared with its F-86A stable mate, is the moving forward of the vertical tail surfaces in The YF-93A first flew in January this year. the stratospheric belt above, say, 40,000ft. The question mark that persists in writing itself across the performance chart is whether this new crop of Air Force heavyweights will be penalized because of wing-area deficiency at high altitudes. If it be assumed that this type of long-range fighter will perform its more serious combat missions within the 20-25,000-lb weight bracket, the corresponding absolute ceilings are estimated to fall within 40-45,oooft with the afterburner tap off and 49-54,oooft with it on—that is, the afterburner boost raises the ceiling about 9,000ft. These ceilings, be it noted, are the theoretical absolute values, not the practical operational or combat ceilings, which are likely to be several thousand feet lower. Bearing in mind, then, the high combat-ceiling of the opposing jet-cum-rocket intercepter, this poses the further opera- tional query: "What happens to the long-range fuel tankage of the escort fighter should the afterburner tap have to be turned on for any considerable length of time in order to protect the bomber? " (One seems to have the choice of running out of either range or altitude!) Perhaps such posers are outside the orbit of the design- engineer, who may be told to keep his nose to the board, and to leave the military problems to the military experts. And so, in the meantime, there is interest in recalling that, from the Anglo-American defensive viewpoint, this latest example of a British jet-unit design married to an American airframe re-establishes the wartime liaison of Rolls-Royce and North American formerly witnessed in the mating of Merlin and Mustang—a particularly happy union, by all accounts. The same kind of breeding strain—Tay crossed with Sabre—bids fair to produce another Derby winner. STRATOSPHERIC STRAWS SOME eighteen months ago, in an article on the trendof U.S. bomber development ("All Jet Bomber Air Force? ", November 25th, 1948), we hinted that, despite detours from the stratospheric highway, caused by the compound-piston and turboprop engines, the signpost would ultimately lead us back to the turbojet, not only for short and medium ranges, but even for long-range bombing. The first two desiderata were generally accepted as met, but the long-range implication was not so apparent in the face of the military planners' billion-dollar faith in the Convair B-36, wherein long range has been obtained at the expense of outmoded cruising speed and small bomb load. Our own viewpoint has always been in favour of the reverse process—to exploit the high- altitude speed potentialities of the jet, gradually working up the range spectrum as the jet airframe is properly matched to its power plant. This same design strategy, incidentally, was brought out by the Navy critics of the B-36 in the recent Congressional investigation, so we Production Stratojet : Boeing B-47As are now coming off the production line at Wichita. Approximately 75 are now on order for the U lited States Air Force.
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