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Aviation History
1950
1950 - 0976.PDF
626 FLIGHT, 18 May 1950 AMERICAN NOTEBOOK . . . feel that we have been thinking in distinguished company. In connection with jet-range economics we drew particular attention to the latest possibilities of the Boeing B-47 Stratojet, pointing out the widespread confusion concerning the gross weight, tankage and range of this aircraft. (Practically every aviation paper in the States fell into the trap set for them by the gentlemen who so adroitly shuffle the publicit 7 cards.) At that time a gross weight of 125,000 lb, bomb load of 22,000 1b, a vast fuel capacity of 15,000 U.S. gallons and a picayune range of 2,000 miles, were all dealt out from the publicity pack and widely quoted, though a few elementary arithmetical notes on the curl soon showed that none of these cards belonged to the same suit. After rearranging them we hazarded a guess that the current take-off weight was around 155,000 1b, carrying a bomb load of 22,000 lb and a fuel tankage of 10,000 U.S. gallons, pn which basis we estimated the maximum (still air) range at 5,600 miles. We further suggested that with the full built-in tankage of 15,000 U.S. gallons, the take-off gross weight could not be much less than 190,000 lb, adding that this figure hardly seemed feasible at that stage of development (1948). We also estimated that, when this stage was reached in the production B-47, the more powerful 5,000-lb J-47 turbojet (which would then be available) would enable the B-47 to reach a maximum range of 8,500-9,000 miles with a bomb load of 22,000 lb and a cruising speed of 560-570 m.p.h., mostly in the stratosphere. Absolute ceiling over the target with bombs on was estimated at 49,000ft, which meant that the probable operational ceiling would be at least 45,000ft. As it turns out, these straws blown on the west wind were not so badly off course, for Boeing have just announced that "The operational range of the production B-47A is expected to be lengthened materially in normal flight by an additional supply of fuel made possible under new gross weight limita- tions." The ten B-47AS with G.E. J-47 5,200 lb turbojets now under construction at Wichita, will have increased range and load capacity, droppable wing-tanks, and a maximum gross take-off weight of 185,000 lb, most of the extra weight differen- tial being charged to increased fuel load, which is in line with our earlier figure-juggling on the basis of a maximum tankage of 15,000 U.S. gallons. Bomb load is now quoted at 20,000 1b • and the sendee ceiling as "over 40.000ft," while the RATO boost has been increased from 18,000 to 20,000 lb, giving a total take-off thrust of approximately 51,000 lb. A more accurate drag analysis of the B-47, plus the proba- bility that our original altitude-cruising consumption of 0.95 lb/hr/lb was a bit too optimistic in the light of near-future jet performance, inclinesfins to drop our range sights by as much as 1,500 miles or so; i.e., down to 6,800-7,500 miles, if based on specific fuel consumptions of 1.0 to 1.1 lb/hr/lb at stratospheric levels where most of the cruising performance occurs. (Only the first 16,000 lb of the 95,000-lb fuel load must be consumed below 35,000ft.) Overall cruising speed will rise from about 540 m.p.h. below 35,000ft to a constant 575 m.p.h. in the stratosphere, climbing all the way to the target, and return. Cruising ceiling over the target, with bombs on (gross weight, 124,000 lb), should be not less than 42,000ft, but the absolute full-power ceiling shows up as 48,000ft with bombs on and 51,000ft after they have been released—figures which certainly bear out Boeing's modest claim of a service ceiling "over 40,000ft." In the absence of model data on the drag-rise characteristics of the B-47 configuration at high Alach Numbers, top^speed estimates cannot pretend to be of the same order of accuracy as the rest of the performance chart. Nevertheless, since the performance art is a fascinating one, we will risk our reputation and predict a maximum of around 610 m.p.h. at 35,000 ft at the target weight of 124,000 lb, while at 45,000ft we believe the B-47A is still good for a mile or two over 600 m.p.h. This, again, backs up the Air Force's current designation of the B-47A as " a medium bomber in the 600 m.p.h.,class." The significant point to note, however, is the remarkably high cruising speed in the target area, compared with the piston-cum-jetted B-36D. Boeing's Wichita division has recently been awarded a $303-6 million contract for 82 B-47A and B-47B Stratojets, which works out at §3-7 million per aircraft. This quantity is believed to include the ten B-47 As* now on the production line at Wichita. (Convair, by the way, were close runners-up in Uncle Sam's gold-coated Easter-egg hunt, receiving a 1950 contract totalling $267.8 million for 47 B-36 and RB-36S; i.e., $5.7 million each.) Boeing have also landed a $4.1 million contract for modifying one B-47 model into a four-engined B-47C (since re-designated the YB-56). According to news re- ports, the YB-56 will be powered by four Allison J-35-A23 turbojets, each developing 9,700-lb thrust; i.e., a total of 38,800 lb, as against the 31,200 Ib of the present six-jet. Since we believe the current Allison J-35-19 and -21 models are rated between 5,200 and 5,600 lb, it seems highly probable that the quoted figure for the -23 model is the boosted value with afterburning. (Even jet units are not given to achieving jumps of this order with the same basic model number.) If this be a fair assumption—and, of course, we are guessing in the dark—then the range may be less, but the top speed a bit higher, though not as much as might be expected, due to the aforementioned steepness of the drag rise after Mach 0.90. Our own estimate for the YB-56 would be close to 62D-625 m.p.h. (M=o 94) at 35,000ft—a figure which takes cognizance of the lower pod-drag of the four-engined arrangement. It is quite conceivable that the drop in range might be recovered by increased fuel load (carried in external wing tanks), as the result of the lower power-plant weight. What these stratospheric straws signify is a 7,000-mile 600- m.p.h. high-altitude jet bomber now coming off the production line. Another two years or so, for operational shakedown and routine perfection of the air refuelling technique, and the B-47 (or B-56) will make both the B-36 and the B-50- com- pletely demode. For the immediate future, Boeing would seem to be in clover—although higher up the mountainside the pasture may not be so verdant. But what of Convair? Per- haps they will make the next move with a delta-winged jet bomber, as the natural sequence to their present work on the XF-92 delta research project which, we gather, has made over 70 successful test flights so far. By slicing off the top of the drag mountain, the 800-m.p.h. jet bomber is now in sight on the supersonic side of the slope. FORTHCOMING EVENTS /-, •" J.,:\ May May May May May May May May May Jyne jufte June .'une June June June June June June June June June June June June June June July July 19.19-21. 20. 20-21. 25. 27-29. 27-28. 28-29. 29. 2-4. 3. 3-4. 3-4. 4. 4. 4. 10. 10. 10. 10-25. II. 15-18. 16-19. 17-18. 17. 18. 24-26. 1-3. 2 Bomber Command Night, Royal Alberc Hall. Air Tour of Sicily. ^ Northamptonshire Aero Club : "At Home." Yorkshire Aeroplane Club : International Rally. Sherburn-in- Elmet. R.Ae.S. : 38th Wilbur Wright Memorial Lecture, by Sir Richard Fairey, M.B.E. Champagne Rally, Epernay-Plivot. Bembridge and Sandown Aero Club : Rally Ailes d'Azur Rally, Cannes, West London Aero Club: S.S.A.F.A. Display, White Walthapt. Tyrol Rally, Innsbruck. Derby Aero Club ; " Ac Home " ind Display. " Wines of Anjou " Rally, Angers. Ultra Light Aircraft Association : Rally, Fairwood Common. F.A.I. : General Conference, Stockholm. Aero Club of Normandy : Aerobatic Competition. Ragosine Trophy Navigation Competition, Rearsby - Blackpool and Fylde Aero Club : "At Home." ._ ' ' Darlington Flying Display. Yorkshire Aeroplane Club : International Rally, Sherburn- in-Elmet, Leeds. Brussels International Aeronautical Exhibition. Fete A£rienne d'Oriy, Paris. Benelux Air Tour. Aero Club de Roussillon : Perpignan Rally. Normandy Rally. Wolverhampton Aero Club : King's Cup Race. Wolverhampton Aero Club : Goodyear Trophy Race. Le Touquet Rally. R.Ae.C. : Members' Deauville Rally. Northern Heights Model Flying Club : Gala Day, Langley Airfield. July July July July July July July July July July July July ; July July Aug. Aug. Aug Aug Aug. Sept Sept. Sept. Sept. 2-9. 3-16. 7-8. 8. a-10. 14-16. 22. 23. 22.23. 22-30 23. !7-Aug 29. 29 5. 6. 19. 19. 26. 2. 5-10. IS. 16. Aero Club of Italy : International Air Week. Aero Club of Sweden : International Gliding Contests, Orebro. Royal Air Force Display, Farnborough. Wiltshire Flying Club : "At Home." '" •'••• R.Ae.C. : Members' La Baule Rally. ' Cognac International Rally. Yorkshire Aeroplane Club : International S.B.A.C. and Air League Cup Races, Sherburn-in-Elmet, Leeds. St. Albans Model Aero Club • Annual Rally, Handley Page Airfield, Radlett. ktra Club d* Tpuraine , Tours Rally. Derbyshire and Lancashire Gliding Club : National Gliding Contests. International Military Air Pentathlon, France 5 Holy Year Rally, Italy. Newcastle-upon-Tyne Aero Club : Norton Griffiths Trophy Race and Grosvenor Cup Race (both International). Wool- sington. Royal Netherlands Aero Club : International "Squadrons" Competition, Ypenburg. Liverpool Flying Club : "At Home." Cowes Aero Club : Display. Association of British Aero Club, : Summer Convention. Swansea and District Flying Club : Kemsley Trophy Race (International), Fairwood Common. Swansea. Wiltshire Flying Club : Thruxton Races. Coventry Aero Club : Siddeley Challenge Trophy Race, Baginton, Coventry. S.B.A.C. Flying Display and Exhibition. Battle of Britain Day. R.A.F.: "At Home "Day. • ,.
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