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Aviation History
1950
1950 - 0764.PDF
FLIGHT, 20 April 1950 Kind to air particles : This head-on view of the Northrop YB-49 Jet-Wing bomber illustrates its clean, drag-free toes and landing-gear design. The YB-49 was an eight-jet conversion of the piston-engined B-35. ,; ..- .• * . CHRONIC SONICS Variations on a Theme by Mach—with Machiavellian , Undertones—as Reflected in U.S. Bomber Design By Stanley H. Evans, F.R.AcS., A.F.I.A&S. Designed as a companion-piece to the same author's " Tonic Sonics," published in " Flight" of January 5tb, in which he discussed the implications of current U.S. jet- fighter design, the present article shows how involved are the problems of bomber layout in relation to the various supersonic imponderables. The biggest riddle facing the designer is whether to " jump the transonic hurdle" by going direct to the. delta wing rather than to devote further time to experiments with- tfe* arrow or the ecaudate plan- forms—configurations already reached in the fighter. Stanley H. Evans—an Englishman resident in the United States—regularly contributes his "American Notebook" to these pages. - A RECURRENT source of surprise to the Britishobserver of the American political scene is thequasi-autocratic power vested in the executive arm of the American republican form of government. To the parliamentarian, it would almost seem as if the principle of the divine right of kingship—which in England once cost a king his head—had been transferred in America to the presidential office. The people vote and the Congress legislates, but the President stall has considerable power of veto to hold up, or at least slow down, the legislative horses. With a little help from the Treasury, some of the horses can be put on short rations and locked in the stable for quite a while. In the aeronautical firmament this executive power has been strikingly manifested during the past year in the baulking of the 70-group Air Force, the legislation for which, was passed almost unanimously by both branches of Congress, presumably expressing the sovereign will of the people. Under executive ruling, however, the U.S.A.F. has been kept on a 48-group diet, perhaps in deference to a five-billion dollar deficit in the national exchequer. And so, in concert with an economy-conscious Executive, a year or so ago Defence Secretary Johnson scuttled the U.S. Navy's big carrier after the keel had actually been laid. Now comes news that the Air Force, reportedly for economy reasons, may drop the XB-52 super-bomber, Boeing's big-brother sequel to their own B-47. Confidently predicted as the long-range jet answer to the B-36, the XB-52 has been variously reported to gross anywhere between 400,000 and 500,000 lb, while the power potential was estimated on the basis of eight 10,000-lb turbojets strung out under the wing in much the same fashion as on the B-47. American newspapers quote the following official state- ment:" As part of its continuous review of existing and planned programmes, the Air Force is examining, among other things,the plans for the B-52; however, no actual decision has yet been reached whether the B-52 will be dropped from its present position as the planned successor to the B-36.Studies are being made to determine the extent to which the B-36 may logically be expected to develop with changes in design and power." In the latter connection, it is unofficially reported that the Air Force is considering replacing the B-36's six piston- engines with new turboprops, either Allison 5,500 h.p. XT-40S or the 5,000 h.p. Pratt and Whitney, in order to increase the speed and altitude. Another news puff now wafting on the breeze claims that the Air Force is modify- ing the B-36 wing into a swept-back design similar to that of the Boeing B-47. At first blush, the idea of turbopropping the B-36 appears a logical development, especially in view of Convairs current design programme with the Convair-Liner and the Navy XP5Y-1 patrol boat. By replacing the existing 3,500 h.p. Wasp Majors with the 5,500 h.p. turboprops now avail- able, a sizeable jump in performance might be expected. (One recent report makes the bold claim of 500 m.p.h. at 50,000ft!) A second look, however, at the power available upstairs in the stratospheric belt—which is the only zone of interest in strategic bomber design—may njeh some of the gilt off the gingerbread, since the highly supercharged model of the Wasp Major R-4360-41 developed for the B-36 may actually give more, or at least as much, power at 35-4O,oooft as the Allison XT-40 or its P. and W. competi- tor. While the turboprop might conceivably score by virtue of its higher cruising power ratio under optimum- range conditions, the overall gain vis-a-vis the highly super- charged piston engine is considerably lower than appears at first sight. A closer study might even show the Wasp Major to be superior at combat altitudes. The swept-wing proposal is even more difficult to diag- nose, since the piston-cum-jet B-36D is reported to have a top speed at altitude, with jets operative, of only 435 m.p.h. Because of the thick wing-section, tapering from 22 per cent at the root to 17 per cent at the tip, the critical Mach limitation is low—approximately 0.70 or, roughly, 460 m.p.h. at 35-4o,oooft. If, then, lie turboprop power at altitude is little better (or even inferior) to that of the Wasp Major, the critical M is unlikely to be exceeded—in which case, the necessity for increased sweepback appears obscure. It is just possible that it may arise from the static balance change occasioned by the substitution of a tractor- propelled power-plant for the existing pusher installation. Still another report—and this one seems to rate more credence—says that the B-36F edition of the Big Stick will be powered with the new Pratt and Whitney R-4360-53 piston-cum-turbo compound engine. This is the latest ver- sion of the VDT (variable-discharge-turbine) installation, reported to deliver a maximum of over 4,000 h.p. (Earlier reports quoted 3,880 h.p. at 30,000ft, with a corresponding top speed of approximately 420 m.p.h.—albeit without
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