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Aviation History
1955
1955 - 0610.PDF
610 FLIGHT MORE THOUGHTS ON JET LIFT * ^ 1.6g. Six of the jets, not required for support, could be kept fullydeflected throughout the landing run, so that, with fifty per cent reverse thrust from the main engines, the retardation would not fallbelow 0.52g at the end of the run, giving a mean figure of about 1.3g. The aircraft could be brought to rest in little more than10 seconds, burning 1,250 lb of lift fuel in the process; a 5-second let-down at 230,000 lb weight would consume another 500 lb,giving a total of 1,750 lb, representing a further saving of 4,500 lb. This seems to be about the best we can do while still retainingthe ability to take off and land without any ground run. We have incurred the additional weight of jet deflectors fitted to 30 of thelift engines; but we have dispensed with the other 20 altogether and have reduced our gross lift fuel requirement from 18,000 1bto 7,500 lb, thus increasing the payload by, in round figures, 30,000 lb. There is a further case yet to be considered. Suppose we takeout another six of the lift engines, retaining just enough to allow us to land vertically. Then at take-off the aircraft will have aneffective weight of 60,000 1b even with all jets running. It will have to make a normal take-off from a runway, and with a wing-loading equivalent to 60 lb per square foot it will run 1,500 feet before unsticking. It obviously would not pay to run the jets atall while still on the ground; they would be opened up, vertically, when the wing lift had risen to 60,000 lb, and thereafter the take-offwould continue as before, except that with only 24 instead of 30 jets available the acceleration would be less; the air-borne panof die take-off run would occupy about nine seconds, and the fuel consumed would be about 1,000 lb. In the landing case, thereduced lift thrust available would mean a longer landing run of about 15 seconds, and the total lift fuel consumed would be about2,000 lb—slightly more than before. The net saving in lift fuel would only be about 1,500 lb, to which must of course be addedthe weight—6,000 lb—of the engines taken out. But it is at least questionable whether this saving would be enough to compensatefor the extra weight which would have to be built into the under- carriage to permit of a runway take-off; and when one takes intoconsideration that we have lost die very valuable ability to take off from any surface without ground run, I think it will be agreedthat this is not worth while. I should like to emphasize that none of the figures I have given has any pretence to exactitude. In arriving at them I have sim- plified problems, straightened curves and cut corners generally; but unless I have been guilty of some egregious howler I hope that they may be taken as reasonable approximations. If they are, we should be able to draw certain conclusions from them, as follows: — (a) The amount of jet lift to be provided need never exceed die maximum all-up weight of die aircraft. (b) With jet lift equal to the max. a.u.w., an aircraft could leavethe ground with no run, and if fitted with jet deflectors could climb away at any initial angle; but steep angles of climb wouldentail an appreciable weight penalty and should never be pro- longed further than necessary. The penalty for angles of 15degrees or less would be negligible. (c) Vertical take-off on an even keel would be both expensiveand unnecessary. (d) An appreciable saving could be effected by compensatingfor varying wing lift during the take-off and landing runs by deflecting all lift jets instead of varying the total lift—but at theexpense of considerable accelerational discomfort to passengers. (e) When used in the most economical way, the lift engineswould not require an exorbitant provision of fuel—not more than 2-3 per cent of the a.u.w. (0 No practical advantage would be obtained by providing jetlift equal to less than the a.u.w. The results of our various modifications are summarized in thefollowing table. Original design ... "Mkll"(lift-a.u.w.) "MkllA"(deflectors) "Mk III"(reduced lift) Take-off Vertical No run No run Runway1,500ft Effectiveclimb angle 2°2O-* 5° Any angle Any angleafter unstick Jet lift Ib 500,000 300,000 300,000 240,000 Lift fuel Ib 18,000 14.000 7,500 6,000 Payload Ib w w + 24,000 w + 30,000 w + 37.500 * 300ft vertically, followed by 7,500ft horizontally. BREGUET PROJECTS A Military Version of the Integral, and an Anti-submarine Vultur /COINCIDENT widi the news of the death of Louis Breguet^ (see page 606), reports have appeared of yet another of his famous company's projects. This latest, a military version of theBreguet 940 Integral, has been given the type designation Br.941. The layout and principles of the civil-transport Integral wereoutlined in Flight of February 25th. Broadly speaking, the object is to produce a fixed-wing aircraft which could utilize a helicopter'slanding-ground and yet be less vulnerable to engine failure on take-off. The type 940 has a high unbraced wing widi a spanof 52ft fitted widi double flaps and mounting four 13ft airscrews driven by four Turbomeca Turmo turboprops mounted in die BREGUET 941 (Two Twin Turmos) two inboard nacelles. All four airscrews are linked by a transverseshaft so diat engine failure will not stop any one airscrew. The outboard airscrews can be used by the pilot for directional control.A further small turbojet in the tail is deviated to give additional directional control at very low speeds. The type 941, of which a three-view drawing is shown here,is a military assault-transport version of this project. The fuselage differs mainly in having provision for a large rear-loading doorunder the tail. The four Turmos will be disposed in four separate nacelles and will each drive one 13ft airscrew. (In the Type 940die same power is obtained from two twin Turmos in the inner nacelles.) The Turbomeca Marbore II in the tail iseliminated. The main landing wheels are no longer on out- riggers, but are carried on plain compression struts. Models of the 941 will be on view on the Breguetstand during the Paris Show in June. The aircraft is intended to take off in 64yd and to carry a 6,600-lb loadfor 620 miles. Another Breguet project, the single-engined anti-sub-marine version of the Br.965 Vultur, has now flown. The first aircraft is in fact die second Vultur prototype con-siderably rebuilt to house in die after fuselage a retract- able "dustbin" radar scanner instead of the Nene, andtwo large pinion containers (for either weapons or detection gear) just ahead of the main undercarriage legs.The ample cockpit canopy now contains only one seg- ment of transparencies. The modified Vultur is a precursorof the first prototype Br. 1050s which are due to fly in the early summer of next year. There will be five of them.Two types of engines are reported by a French source to be under consideration—either Armstrong SiddeleyMamba 6 of 1,650 h.p. or the Rolls Royce Dart RDa.7 of 1,950 h.p. The aircraft will be armed widi a fullrange of detection gear, now being tested in the modified Vultur, and witii rockets and depth charges. Loadedweight will be 17,900 lb, maximum speed 270 m.p.h., and ceiling 19,200 ft.
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