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Aviation History
1944
1944 - 1762.PDF
FLIGHT AUGUST 24TH, 1944 ENDURANCE AND RANGE is in the relation to that speed For the example repre sented in Fig. 2, a wind of 60 m.ph. is 46 per cent, of the optimum climbing speed (130 m.p.h.) 0.46x130 = 35; 130 + 35 = 165 m.p.h., which fairly well corresponds to the optimum speed foi that wind on the graph. When making experiments the pilot must remember that the air speed determines the range only when the weight of the aircraft remains unchanged. The most favourable conditions for attaining the greatest possible range depend primarily on the choice of the optimum angle of incidence. If we want to fly level at a lower speed we must increase the angle of incidence and vice versa. If, however, the weight is increased, then at the same angle of incidence the speed must be increased, otherwise the aircraft begins to descend, increasing the. angle automatically. Thus air speed is a good indicator of the angle of inci dence, so long as the weight of the aircraft remains un changed. The optimum speed for the same aircraft, but with different loads, is different. It is easy to prove that retaining in all circumstances the best angle of incidence requires a change of speed according to the ratio * V" v3 G. Here V, and V 2 are the indicated air speeds. G, and G3— weights. This simplifies the question of how to find the optimum speed if the weight of an aircraft is changed. In an aircraft the loads carried do not as a rule make any CYCLONES NEW FINS A NEW engineering design which will permit greater horse power output of air-cooled aircraft engines and which will also save 24.000,0001b. of highly critical alloy steel per year iias been announced by the Wright Aeronautical Corporation. Developed in co-operation with Wilhelm B. Bronander, of the Scandia Manufacturing Company, of Arlington, New Jersey, the new design makes possible the use of aluminium cooling fins on steel cylinder barrels, with the steel-aluminium combination giving almost twice the cooling area of the all- steel fins. Sixty fins can be mounted on a barrel in the same space formerly required for 40 steel fins machined from the barrel wall. The increased cooling area, coupled with the fact that aluminium can dissipate heat more rapidly than steel, results in cooler operation, and in turn permits more power to be taken from the engine. It is particularly important on military aircraft, where sustained operation is frequently required at high percentages of power. The improved cooling also results in longer life for piston rings. Formerly, cylinder barrel fins were machined by cutting 40 narrow grooves, eaeh five-eighths of an inch "deep, into a solid steel barrel with a wall three-quarters of an inch thick. This machining reduced the actual thickness of the cylinder wall to one-eighth of an inch and also left standing on the barrel 40 fins, each fin with a thickness of only 25 thousandths of an inch. The new fin, known as the " W " fin, eliminates this difficult machining operation. The " W " fin is produced by folding a strip of sheet aluminium into the form of an extremely exaggerated letter "W," with the two outside legs one inch high and the centre portion only one-eighth of an inch in height. These strips are cut to size, shaped into half-circles and then snapped into shallow dovetail grooves cut into the barrel. A special tool then rolls over the short centre section of the "W," flattening this section and wedging the outside legs of the " W " into the dovetail grooves. This wedging not only holds the fin firmly in place but also provides a broad contact area through which heat can pass from the steel wall of the barrel into the aluminium fin. The aluminium fins can be made, to almost any desired height, while the steel fins had virtually reached the maximum depth to which they could be cut in quantity production. While this new barrel does not materially affect the over-all weight of the engine, the saving being only one pound per cylinder, there is a very important saving in the quantity of raw material required, the rough forging for the new barrel being substantially lighter than that for the older model. In one year's production of Cyclones, this saving will amount to 24,006,0001b. considerable change in the total weight. Bearing this in mind, it will be found that a simple and quite accurate approximation for practical purposes may be arrived at^A by calculating the required speed as follows: — If the weight of an aircraft increases X per cent, then it is necessary to increase the speed £ X per cent. In the samo way a decrease in weight of X per cent, should be accompanied by a decrease in speed of £ X per cent. This shows the reader why a lower speed is always recom mended on the return journey. When flying with a lesser load the speed should be lower in all circumstances—climb ing, cruising or turning—if the pilot intends to fly always with the greatest possible efficiency. It may be mentioned that a more heavily loaded aircraft has a diminished range. This is evident from the fact that a greater weight requires a greater speed at the same angle of incidence. The power required for an increased speed at the same angle of incidence increases much more rapidly than the speed itself (in proportion to the third power of speed), Corresponding to the increase in power, the rangc._ is diminished. A~ Lastly, when, trying to get maximum range in given co*!|A ditions, a pilot must lemember the possibility of exploiting a favourable wind. Winds of different directions and strengths blow at the same time at different altitudes, and it is obviously advantageous to fly with a favourable wind. No one has evei seen migratory birds bound on long journeys flying against the wind. They always choose the time and altitude at which favourable winds help them to cover long distances If operational necessities do not require otherwise, every pilot should follow their example. _ Thj old Cyclone cylinder (left) and the new. QUICK WORK BY R.N.Z.A.F. "PHE assembling line method has been adopted at the -*- R.N.Z.A.F. engine repair depot in the Waikato district for engine overhauls. This method has .been such a success that the time for stripping, overhauling, and reassembling aircraft engines has been cut to less than half what it was under the old system. Even in the United States the times set by the R.N.Z.A.F. engine repair section have not been bettered. AT.A. BENEVOLENT FUND W E are pleased to record the receipt of contributions amounting to £168 10s. to the above fund since our last statement appeared in the issue of May 25th. These bring the total of outside contributions to August 14th to £9,892 17s. id. Already acknowledged ^9,724 7 1 Subscriptions by A.T.A. and B.O.A.C. members 4,102 1 6 Dunlop Rubber Co., Ltd 105 o o Ropey. Old Pilots' Association 50 o o Fit. Lit. J. Mill, R.A.F., Ceylon 5 o Sqn. Ldr. G. T. Stoneham, R.A.F 5 o o Mrs. Hawkins, Hartley Wintney '2 o ^e Anonymous (May 19th) 10 « Anonymous (July 6th) 0 o Miss J. M. Smith, Aldershot 5 o £13,994 18 7
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