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Aviation History
1933
1933 - 0207.PDF
JULY 27, 1933 47 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT < * K J H \ VI v. * \ s 5 * a /- ^ / /—-— N < i » • « o ^-"^ / 1 >J ; i i i i i i 1 I i i i i i i i i i i ! 1 •/VwifJIiw/A' -0 , 1 1 1 1 1 1 •> J i-^-rji * r 1 I - a 4-" * T v 1 Wf/t •."•-. N 1 •f 1 rv » - 5 -: v! • -! •i * * * N H % $ \ 1 - X p . ' 1 .. f * i Hi -J 1 | 1 ! • if, *• « i VI * 5, 1 Q * 0 S) 5 -?> I I r r> The total span of flap was 45 ft. Total area of flap, 93.8 sq. ft. Two calculations of forces were made for the simple flap, one a maximum angle of 60 deg. and the other a maximum angle of 45 deg. The mechanism for operating the simple flap was the most efficient in our opinion, and the geometry chosen seems to be the one requiring the smallest effort on the operating crank handle. The Zap fl ap geometry and operating mechanism is approximately the same as that developed by the B/J Company when Zaps were supplied to the XOJ-1 observation aeroplane for the Navy. A photo graph of the XOJ mechanism is shown in Fig. 13, while Fig. 1 shows a schematic view of the Zap toggle mechanism. When a comparison of lift coefficients is made, it is seen that even though it were practical, from an operat ing force standpoint, to get the straight hinged flap down to 60 deg angles, in order to obtain the benefit of large drag, the lift would be materially less than the Zap flap, and, in fact, less than its own 45 deg. position. (See polar curves, Fig. 7.) With the Zap type of toggle arrangement, wherein the leading edge of the flap slides back and the toggle is concealed in the wing in such a manner that one end 01 it is located close to the centre of pressure of the flap arid the other fastened to the structure at the top of the rib, it can be seen from Fig. 6 that the number of turns on the operating crank and the forces necessary "c extremely low, in fact, with certain types of air foil permitting a more favourable geometry of the ]?aP linkage, it will be possible to have actual opening forces. h's phase of the Zap mechanism is extremely impor tant when it is realised that light operating forces have two v(Ty important results: First, in that the weight 1 the operating mechanism can be considerably less, an" spcond, even more important, the fact that in an emergency landing, it enables the pilot to get the flap own quickly. In an existing monoplane which has 754 recently been flown in the United States, a straight hinged flap is utilised in conjunction with Zap ailerons for lateral control and the operating forces are so great as to require 45 turns to get the flap down to 45 degrees with a lift increase of only 35 per cent. It can be seen in Figs. 7 and 8 that the maximum lift coefficients of the Zap flap at 60 degrees is 0.00615 and also from Fig. 7 that the straight hinged flap has only a maximum lift of 0.00545. These curves were developed by inter polating the data in NACA Report No. 422, because this report did not test the best Zap flap position but took two flaps on either side of its general location. It must be borne in mind, however, that the angular movement of the flap and the lift coefficients obtainable are inti mately connected with the practical results than can be obtained and which, of course, depend upon the operat ing forces and the time required to get the flap into action at maximum lift. In Figs. 8A and 8B are shown the lift coefficients for a staggered biplane with the different flap settings on upper and lower wings neces sitated by the stagger. Figs. 8c and 8D show wing and flap arrangement. (To be continued) ENGINE RESEARCH Engineering is not an exact science. In all proba bility it never will be. Good design depends upon experience and good judgment quite as much as upon calculation. This applies particularly to the design of cylinders for all internal-combustion engines, but perhaps in the greatest degree to the design of air- cooled cylinders for aircraft engines. There is no doubt that it was these considerations that led the engineers of Armstrong Siddeley Motors, Ltd., to design and produce a research engine of particular merit. g
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