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Aviation History
1949
1949 - 1980.PDF
746- FLIGHT, 8 December 1949 AERODYNAMIC CLEANNESS : :...: twice the ventilation air they required, he guaranteed a loss ofthrust, and consequently a loss of payload, equivalent to that of five passengers.If the losses in the system were reduced to a minimum and the pressure relief valve designed to give gradual expansion and no lossof energy, some 700 lb of payload could be gained. For this reason, improvements on existing arrangements should be developed. Having dealt with the past and present methods of achievingdrag reduction, Mr. Richards went on to tackle the much more difficult task of reviewing the likely changes in conception in thefuture. On the subject of tailless and all-wing aircraft types, the lecturerobserved that, since all the drag arose from the wing itself, wing protuberances and the extent of laminar flow were of over-ridingimportance, fn order to demonstrate this effect, a tabulation of analyses had been made of a series of aircraft embodying variouschanges of conception and designed broadly around the duties of the Brabazon II, all being assumed to have a gross weight of*•/*••". lb and all fitted with eight Bristol Proteus engines. The series was as follows: — (A) Orthodox Brabazon type with and without extensive laminar flow. (B) Tailless pusher with orthodox wing sections. (C) Orthodox Brabazon type fitted with thick suction wings. (D) Tailless pusher with thick suction wings and with same planform as type B but with the wing loading increased to 45 lb/sq ft. This was feasible by the use of the double-decker layout and the thick wing. Since the engine power suffered badly from loss of ram if the engines sucked awayair directly, auxiliary blowers coupled to two engines were assumed. (E) As in D, but with the aspect ratio increased to 6.5 in order to make use of the higher wing loading. (F) As for E, with the thick suction wings confined only tothe central passenger-carrying area, the outer wings being conventional aerofoil shapes (necessary in order to reduce tomanageable proportions the mass flows involved with for- ward transition). (G) As for E, but with suction obtained directly from the enginesinstead of from auxiliary blowers. Included to demonstrate the lack of ability of the engines to handle the large suctionmass flows in the event of early transition turbulence on the wings. Startling Possibilities ' --..-" In Fig. 4 was shown the nominal payload-range characteristicsof the orthodox Brabazon type aircraft fitted with tractor airscrews and, alternatively, with pusher airscrews and smooth wing con-struction, thereby allowing transition to be delayed to 50 per cent chord. It could be seen that the 25,500 1b payload carried by thebasic aircraft was nearly doubled in these circumstances, an ex- tremely handsome bonus arising from laminar flow. It could alsobe seen from the nominal payload-range characteristics of the tail- less project that the advantage in performance of the tailless typeswas closely associated with payload to obtain more benefit from extensive laminar flow and that, with transition at the leading edge,no gain was to be obtained with this layout. With extensive laminar flow, however, the tailless layout would give a 140 per centincrease of payload over the orthodox tractor aircraft and a 25 per cent gain over the pusher type of orthodox aircraft. During the past eight years research into boundary-layer controlby means of suction had taken new life in this country, and its possibilities were startling. The advantages were gained in twoways, which must be differentiated: (a) the suction reduced the basic drag coefficient, thereby improving tie performance, and (b)it allowed the use of sections of large thickness/chord ratios—up to 30 or 40 per cent, or even more—thereby also permitting a moreefficient structure, a higher aspect ratio and increased space. The lecturer presented curves which showed that, unless a slotwas used, placed very far aft, little was to be gained from the use of a 16 per cent thick-suction wing as opposed to a normal wingof the same thickness with transition a long way aft. In view of the 10QOO0 CONVENTIONAL AIRCRAFT /'(>5cJTRANS'T'ON POINT TAILLESS AIRCRAFT TRANSITION AT 0-1 c 1 O-5c20,000 Fig. 5. Thickness/ chord ratio re- quired on all-wing aircraft in order to accommodate passengers. ASSUMPTIONS :— Aspect ratio, 6.0Taper ratio, 3.0 Height, one deck 7ft.Height, two decks, 15ft. complication andadded weight in- volved, this type of16 per cent aerofoil could be immedi-ately discarded. On the other hand, the30 per cent suction wing, while givinga slightly higher drag, showed a bigadvantage with tran- sition very far aft; 100,000 200P00 300,000 400,000 MOjOOO AIRCRAFT A.U.W. (Ib) furthermore, it provided the essential advantage of greater space anddepth of structure. If, on the other hand, extensive laminar flow could not be obtained, the drag of such a section was appreciablyhigher than that of the orthodox 16 per cent section, and the struc- tural advantage must be weighed against the drag increase.The analyses which he had presented, said the lecturer, were essentially linked with the need to cany passengers; thus, thebest thickness/chord ratio for the all-wing aircraft was dependent on the overall size, because, to carry passengers, the cabin heightmust be about 7 or 8ft on a single decker or about 15ft for two decks. Fig. 5 showed the minimum thickness/chord ratios possiblein accommodating passengers for various aircraft weights and wing loadings. It was found that for an aircraft of 300,000 lb all-upweight, and space to seat the passengers of the basic aircraft, the maximum feasible wing loading was 30 lb / sq ft and that the neces-sary depth could be obtained with a wing section of about 15 per cent thickness/chord ratio. Thus the plan form w&s. rather waste-ful on the single-decker, tailless type, but came into- its own with the use of thick-suction wings of about 30 per cent thickness / chordratio. The better structure also allowed an increase of aspect ratio and wing loading, which the large thickness/chord ratio couldprovide without cramping the height of each deck.. The tailless principle could be used to far greater-advantage withthe thick wings made possible by the use of suotron. Drag coefficient for a suction wing was only a. little less thanthat of a conventional section with transition at 0.5 chord. Fur- thermore, the structural weight-saving was offset by the weight ofthe suction plant and ducting. Consequently, there was little overall gain, and every disadvantage, in that still more laminar flow wasneeded, while the thick-wing stability and control characteristics with and without suction had to be made satisfactory. Efficiencyof the aircraft was not greatly improved by a higher wing loading, higher aspect ratio and reduced area. It might be concluded, there-fore, that the improvement in cleanness by using a thick-suction wing was not significant unless the overall drag of the aircraft was 100000 2000 10.000 1,000 6,000 7,000 Fig. 4. 2D00 3,000 4/100 5,000 STILL-AIR RANGE (n.m.) Payload/range characteristics, orthodox and tailless types. 4jOOO 6,000 6,000 STIUl-AIR RANGE (n. m.) ()) Orthodox aircraft, transition at 10 per cent chord (type A). : (2) All-wing aircraft, transition at 50 per cent chord. (3) Atl-wing, suction-profile aircraft, transition at 71 per cent chord, aspect ratio5.0 (type D). (4) All-wing, suction-profile aircraft, transition at 71 per cent chord, aspect ratio6.5 (type E). Fig. 6. Comparison of payload/range characteristics for all- wing suction-profile, all-wing and orthodox types.
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