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Aviation History
1953
1953 - 1222.PDF
378 FLIGHT, II September 1953 HEMISPHERICAL BOMBING . is often dictated by the take-off performance and in some cases is penalized on this score. Flight-refuelling provides a means of bringing an aircraft to a greater flying weight after take-off or, if desired, after the initial climb. The main advantage of an increased flying weight is to be found, of course, in the resulting improvement in range and bomb-load capability. It also has a further advantage under flight-refuelled operation in that the fuel transfer can take place earlier, and thus the tanker is able to deliver a greater quantity of fuel. On the other hand, an increase in the flying weight in this manner generally results in the bomber arriving at the target at a weight some ..here near the normal or take-off maximum. Four flight-overload cases have been considered:— (A) Single outward refuellings, with overload. (B) One outward refuelling, with overload, and one return refuelling. (C) Two refuellings outward at the same refuelling point, with overload. (D)Two refuellings outward at the optimum points for maximum range, with overload. giving a maximum radius of 15.R (Points CCC in Fig. 6.) 2R 22 R P R R1 R2 BOMBING RADIUS Fig. 6. Fuel/range diagram, with flight overload. For convenience the flight overload has been taken as a quantity (a), or one-third of the total disposable load. (In practice, this would represent approximately one-sixth of the normal gross weight or, say, 25,000 lb for a 150,000-lb bomber.) (A) Single Outward Refuelling with Overload.—Maximum fuel transferred is —and takes place at — increasing the maximum J y 14R radius to -—-. Emergency return is possible from the refuelling point (with the assumed capacity bomb-load) and it will be noted thai the distance to the optimum point has been reduced by one-third, having the effect of increasing the fuel transfer by two-thirds. The fuel and bomb-load diagram is denoted by AAA in Fig. 6. (B) One Outward Refuelling with Overload and One Return Refuellitig.—The conditions of the first refuelling are the same as those given in (A) above. The second refuelling takes place at P, \1R giving a maximum radius of ——, or very nearly twice the un- refuelled radius. No emergency return is possible from the second refuelling point. (Points BBBBB in Fig. 6.) (C) Two Refuellings Outward at the same Refuelling Point, with Overload.—In order to avoid the inability to return from the second refuelling point both refuellings can take place together on the outward flight. For maximum range the fuel transfers are at P, (D) Two Refuellings Outward at the Optimum Points for Maximum Range, vrith Overload.—The range can be still further extended, whilst permitting emergency returns from both refuelling points, if the fuel transfers take place on the outward flight at different AR locations. The first refuelling is again at -JJ—,with a second refuel- 4R 2 5i? ling, of one-third the quanaty of fuel, taking place at —3- -r- X —= . 22R . ,. 15.67/? "2Y > giving a maximum radius of — . (Points DDDDD in fig. 6.) Bomb-loads with Flight Overload.—The bomb-loads obtained from Fig. 6 are shown in Fig. 7, denoted by A, B, C and D, and the diagram has been completed by the addition of bomb- loads for a single refuelling, without overload (E); refuellings outward and inward, without overload (F); and two refuellings outward, without overload (G). Over that part of the radius con sidered, i.e. with bomb-load varying between zero and capacity, emergency return is possible from all refuellings, with the excep tions of B and F, which permit of no emergency return from the second refuelling point. It is seen that, for the cases considered, maximum bomb-loads and radii are obtained by the employment of refuelling outward, with overload, and one refuelling inward (no emergency return from second refuelling point); or, if emergency return is necessary from both refuelling points, optimum conditions are obtained with two fuel transfers at different points on the outward flight, together with flight overload. The double refuelling at P on the outward flight with overload gives the same results as the one refuelling outward without overload and one inward, but allows for an emergency return from both refuellings. Practical Example: the 150,000 lb Bomber.—It is considered unnecessary to give an example to include all the factors dealt with so far, and one has been chosen therefore which is reasonably realistic, representative of present-day practice, and which covers the main variables. A bomber with a gross take-off weight of 150,000 lb has been assumed, and with a maximum flying weight of 175,000 lb. Power is supplied by four turbojet engines. The basic operational weight has been assumed to be 68,000 lb (45.4 per cent), leaving 82,000 lb for fuel and bombj. Other assumed data are given below. Fuel excess over cruising used on take-off and climb .. 3,500 lb Excess on descent Circuit, approach and landing .. Stand-off (15 min at 5,000ft) . . Alternate (200 n.m. at altitude) Fuel reserve and unusable fuel .. Cruise fuel for nett ultimate range Capacity bomb-load, assumed .. Fuel consumption, assumed Nett ultimate range (see Fig. 7) It will be assumed that the tanker is of the same design as the bomber and that the weight of flight-refuelling equipment is equivalent to the weight of items that can be stripped from the bomber; then operational weight is 68,000 lb, as before. In this example the simplifying assumption that fuel consumption per mile remains constant has not been used; instead, consumption has been taken as proportional to instantaneous weight, which is reasonably accurate for jet-powered aircraft. Fig. 8 shows that optimum transfer conditions are obtainable at 500 1b 1,300 lb 1,700 lb 2,100 lb 400 1b Total reserves , 6,000 lb 72,500 lb 60,000 lb .. 0.125 "lb/n.n 5,500 n.m. 150 OOO ) WEIGH T (Ib x 3 O REFUEL 2 BOMBERS i MAX. FUEL TRANSFER S^5^ '"^^^j •f 6OOOO lb BOMBS '""" RETURN REFUELLING 50000 lb BOMBS lA^~"^*~~,--»^ ^"""-^^, '""""^XT MAX. RANGE UNASSISTED ' ' 1POO 2DOO 3POO 4,000 BOMBING RADIUS In. a. m.) 5pO< Fig. 7. Bomb load diagram, flight overload conditions. Fig. 8. Fuel load diagram—150,000 lb bomber.
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