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Aviation History
1947
1947 - 0045.PDF
JANUARY O.TH, 1947 FLIGHT JET-PROPELLED FLYING WING and bottom evolved by the N.P.L. in conjunction with asimple aerodynamic form.. The original idea is that of Dr. A. A. Griffith, F.R.S.,who arrived at it when thinking of means of avoiding boundary layer separation in a diffuser. As Mr. E. F. Relf explained in his recent Wilbur WrightMemorial lecture before the Royal Aeronautical Society, the fact that suction could prevent turbulent boundarylayer separation has long been known, and very great in- creases of maximum lift have been demonstrated experi- mentally both here and abroad. The main problem is tcdesign the wing shape to suit the suction. The accompanying sketches depict representative typesof "flying wing" aircraft. Although not strictly in this class the Junkers G.38 is included as it exemplifies its de-signer's strivings towards his ideal of the "all wing" machine. G. S. (Readers might also like to refer back to the article " Tur-bines and the Flying Wing" published in our issue of May 13th, 1943.) COLD STARTING */ TNFORMATION which had been gathered during 3J years of-*- work by a committee of the S.A.E. Aeronautics Division studying cold-starting requirements for aircraft engines waspublished recently. A summary appears in the Society's journal. , Following concentration on six elements of theproblem—cranking speed, starting power, fuel, ignition, lubri- cation and clearances—basic points emerge. For satisfactory starting at sub-zero temperatures the fol-lowing requirements must be met:—(1) the engine must be turned over at an adequate speed; (2) sufficient power mustbe available for two 30-second cranking periods; (3) a com- bustible mixture must be delivered to the cylinders; (4) anadequate spark must be produced; (5) the engine must receive a usable lubricant; (6) fits and clearances of mating surfacesmust be such that normal functions occur irrespective of the temperature. Additional qualifying data was as follows: The engine mustbe turned over at a speed greater than 20 r.p.m. and a con- tinuous cranking type of staiter gave best results. To deliversufficient power for the two periods, batteries should be kept heated. Normal aviation petrol does not vaporize sufficientlyduring cold weather, high volatile priming and starting fuels are therefore necessary. Several blends of pentane, butane and propane were tested with varying degrees of success, butall tests pointed to the need for careful metering of special priming fuels to eliminate the hazards of fire and structuralfailure due to hydraulic lock. It was further observed that the danger of scuffing of cylinder walls through the washingoff of lubricant was inherent in the improper use of special liquid starting fuels. However, such fuels proved consistentlysuccessful in starting down to —65 deg F. The inclusion of a booster circuit in the ignition systemwas found to be necessary. Fouled and iced plugs were traced to false starting, and moisture condensation to inade-quate fuel delivery rather than ignition malfunctions. Fouling also resulted from the incorrect use of oil dilution. For lubrication, viscosity and " flowability " were the pro-perties to be watched. Viscosity should be reduced by dilu- tion with normal petrol, and the "pour point" of the oilshould be lower than the starting temperature. Difficulties with clearances were overcome simply by resetting.A final recommendation was that post-war work should aim at a suitable metering system for both liquid and gaseousspecial starting fuels, difficulties encountered in using high volatile fuels being directly traceable to improper fuel/airmixtures. SWEDISH JET FIGHTER ./ SfNCE the war, during which its entire output was absorbedby the Swedish Air Force, the Saab Company has concen-trated on the development of civil aircraft, but military types are not being neglected. At present a number of J21 twin-boom fighters are being rebuilt and their Daimler-Benz 605 engines replaced by Goblin turbine jets. A top speed of about520 m.p.h. is then attainable. This conversion, however, is only an interim step towards the Saab 1001 jet fighter,designed for a speed of 650 m.p.h. During the war Saab fighters were made in a plant at Troll-hattan, and bombers in the "rock workshops" at Linkoping. BIGGEST BOMBER L AN announcement by the Consolidated Vultee Aircraft Cor-poration gives some new facts concerning the XB-36 ex-perimental bomber. With its span of 230ft and weight of 278,000 lb, the XB-3G is the largest aircraft now flying, and is claimed to have a normal range, without extra fuel tanks, of 10,000 miles with 10,000 lb of bombs. The maximum bomb load is 36 tons. One of the most interesting facts concerns the undercarriage:the present gear, which uses no-inch main wheels, is to be replaced by eight 56-inch wheels. The improved weight dis-tribution, in conjunction with shorter landing runs permitted by reversible-pitch propellers, should enable the machine tooperate from a greater number of airfields. r' The propellers driven by 28-cylinder Pratt and WhitneyfVigines, are claimed to be the largest yet installed. They are &i Curtiss manufacture, 19 feet in diameter, and have hollowsteel blades with, it is said, the first application of thermal anti-icing on production propellers. The normal crew numbers twelve,-and a four-man relief crewis carried. An 85ft magnesium tunnel connects the pressurized forward and aft crew compartments, "transportation," as thePressrelease puts it, being provided by a " four-wheel scooter." It is further disclosed that the wing is of an N.A.C.A.laminar-flow section with an area of 4,772 sq ft, and that the trailing-edge carries a total power plant weight of 19J tons.The fundamental factor which led to the selection of pusher airscrews was the desire to preserve a smooth airflow over thewing. The nacelle drag was also decreased and directional . stability improved. Largest of the 300 electric motors carried is the 22.7 lb 16 h.p. unit which drives the hydraulic system pump. Smallest is a1/50th h.p. motor opening and closing the carburetter air filter door. For anti-icing and defrosting, engine air, passed throughexhaust gas heat exchangers, is ducted between the double skin on the wing and tail leading-edges, between the double glassof the bomb-aimer's and pilot's enclosures, and to the several sighting blisters. RATEAU TURBO-JETS •"''I T is learned that the Rateau Company of France, whoseturbo jet was described in Flight of November 28th, are working on a much larger design which is to give more than7,700 lb static thrust for a specific consumption of the order of 0.75 Ib/hr/lb thrust. Like the model A.65 or SR.A, pro-vision is made for after-burning, and a portion of the air is to be by-passed. A thrust figure with after burning of 10,500 Ib-is quoted as probable for take-off with this new unit. It will be recalled that on the A.65 approximately one-thirdof the main air flow is by-passed from the fourth stage of the axial compressor, and reintroduced immediately behind thetwo-stage turbine. From here the airstream passes over the tail cone in the jet pipe and additional fuel can be introducedfrom a nozzle in the cone in order to boost the power for a short period at take-off or in an emergency. Some figuresquoted by the Rateau Company with regard to air dilution will be of interest. Taking as an example a unit with a total compression of6.25 without dilution, figures would be as follows: Specific consumption at 560 m.p.h. 1.3 Ib/hr/lb thrust. Static sea-level thrust without after-burning: 1.6 times the thrust at 560 m.p.h. at 16,400 ft, and with after burning: 1.85 timesthe thrust. With a dilution of four, i.e., a total weight of air equal to four times that passing through the turbine, thefigures would be: Specific consumption at 560 m.p.h. at 16,400 ft 1.07 lb/hr/lb thrust. Static sea-level thrust withoutafter-burning: 2.35 times the thrust at 560 m.p.h. at 16,400ft, and with after-burning: 3.5 times the thrust. Although a unit designed to embody a dilution system isa little heavier and more cumbersome, the saving in fuel on a flight of more than one hour's duration at full power wouldbalance the weight increase. Existing turbines ate being started by means of an auxiliaryblower feeding into the inflow channel of the compressor.
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