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Aviation History
1932
1932 - 0100.PDF
SUPPLEMENT TO FLIGHT THE AIRCRAFT ENGINEER JANUARY 29, 1932 Within the limits of experimental error, the following relationship holds for practical conditions of loading for any aircraft. Vc (initial) = V9 + —m ~ V> (4) Vc = Best climbing speed m.p.h. V8 = Stalling speed m.p.h. Vm = Maximum level speed at G.L. in m.p.h. K, = Constant for any particular aircraft. The stalling speed of a normal biplane is based on a maximum lift coefficient of about 0.6 as compared with 0.705 for our monoplane. Therefore, when applying these formulae to a biplane, the stalling speed for the equivalent monoplane should be inserted. The value of this fictitious speed is given by : TABLE V. V„ (equiv. monopl.) = Vs (bipl >A/£ 6 0-705 0-92 V. (bipl.). This equivalent monoplane speed is then used for equations 1 and 4. From the results of Fig. 3 the following table is compiled: — TABLE IV. 5,000 7,000 9,000 160-9 1600 158-0 50-7 60-0 68-0 90-2 95-5 101-1 110-2 100-0 90-0 39-5 35-5 33-1 2-79 2-81 2-72 The point of maximum rate of climb is hard to fix to within +2 m.p.h. on full-scale tests, or by estimation. The small variation of K4 shown in Table IV is, therefore, negligible, so that K4 has a value of 2.77 for an aspect ratio of 6, and an airscrew designed as the one in the example. The change of K^ with aspect ratio is of no particular interest, except for the estimation of best climbing speed where no previous tests are available. 32 3-0 2-8 2-6 2-4 2-2 FIG.7. "0 -I l/A -2 -3 -A- Fig. 7.—Variation of K4 with Aspect Ratio. Table V and Fig. 7 give this variation of K4 with aspect ratio, from which it is found that 2.44 Kt = 3.22 - -*=-— (5) A From these relationships it is now possible to deter mine the best climbing speed at standard ground level for any loading from the known performance at any other gross weight. v„, v8 v(. V —V ' lit * tf v,-v8 K, 3 6 9 156-7 160-0 161-8 60 60 60 100-0 95-5 94-5 96-2 100-0 101-8 40-0 35-5 34-5 2-41 2-81 2-95 REFERENCE. 1 "The Calculation of Airscrew Characteristics.' 1931. See also " Handbook of Aeronautics." FMOHT, February 20. (To be continued.) LIMITS, FITS AND ALLOWANCES. By R. RODGER. (Continued from page 95 of December 25, 1931, issue.) Shackle Pins The general limits for shackle pins are indicated in Fig. 1 and call for no further comment. + 015* - -010' + 010," -•010* l ' + 010" - 0 + -010" - 0 w FIG.l. T -•001" -005" * Rivet Blanks In practice it has been found that in order to obtain the best form of head it is necessary to have the length of the rivet blanks equal to the grip plus 1.5 D, where D is the rivet diameter. This applies to all forms of rivets, both in steel and duralumin. Hole Centres Centres of bolt holes in timber should be within + 0.015 in. of the nominal dimension, and in metal fit tings within +0.010 in. of the nominal dimension. Overall Lengths The overall lengths of timber spars, struts, etc., over 3 ft. long should be within +0.010 in. per foot run, and lengths of 3 ft. and under should be within +0.030 in. The overall lengths or pin centres of metal spars, struts, etc., over 5 ft. long should be within +3^ in. of the nominal dimension, and lengths of 5 ft. and under should be within ± J, in. Hinges The general practice adopted to ensure interchange- ability in a family of hinges is to control side play by location at a master, or datum, hinge covered by fine TABLE V. Limits on Hinges. Master Hinge. Male. Female. Y. - 0001 + 0-001 - 0-005 + 0-005 Hinge Centres. L. ± 0-030 Auxiliary Hinges. Male. X. - 0-001 - 0-005 Female. YMin. + 0-070 - 0-0 96 d
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