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Aviation History
1912
1912 - 0547.PDF
JUNE 15, 1912. [/yew] # * # Nv 1 15 16 39 40 10 19 31 32 17 55 34] 35 36 37 35 ei 20 Z3 1110 357 7"! 6 76S 7ZQ SB'S 053 59© 965 905 16-4 40-2 STS 226 755 57 1V3 452 04-S 21-Z. 5 4-6 (5-4 5T 39 7 125 5 15 O 9 7 73 5-7 410 134-0 10 7 10 2 77 63 46-0 1150 10 £ 9-31 71 ST 33'6 1020 17 7 S6S 66 7-5 45S 1300 20 © to 6 BO 7 0 444 128 5 2o2 104 »« 10 3 46 3 937 20 3 594 SB 9 5 43 5 975 20B 011 69 950 5 3 45 2 11-42 2lO 10 O 76 79^ 7 5 42 1 1037 13 3 925 70 71S 60 3971192 1JO 9 43 72 o09 6 O 33 0 1115 17 6 0 04 63 639 15 3 3>6 4 48 1 17 5 5 5 42 302 U-5 401 65 2 20 O 703 53] 519 19'4 3325 26-3 134 3 35 23 S-35 20 4 5i to 513 17-4 4 01 SO In all the diagrams, the symbols above each column of the table are as follows :— I = inertia of section, i.e., the factor representing the strength of the strut as compared with No. 25, which has a rectangular section. R = resistance in lbs. per 100 ft. at 40 m.p.h. W = weight in lbs. per 100 ft. at 30 lbs. per cu. ft. The final column F 40 is the same as the preceding column except that the result has here been divided by '132 or.Ti„th of the result for No. 51 strut. This facilitates comparison by expressing the results as percentages of the highest value obtained, which is for strut No. 51. In calculating the inertia, the cross section of each strut was traced through its gauge on to squared paper and the areas of the laminee at different distances from the major axis were thereby calculated. The area of each lamina, or row of squares, was multi plied by the square of its distance from the major axis and the sum of these results was multiplied by a constant in order to give the moment of inertia of the section as compared with that of the rectangular strut No. 25 : for details of calculation see example. In connection with the column giving the relation of strength to resistance and weight, if this is to be used for higher speeds, the constant must, of course, be modified. For example, the resistance at 80 m.p.h. would be quadrupled and the factor 6 thereby changed for the factor 24, or thereabouts. The resistance of any shape at 40 m.p.h. in lbs. per sq. ft. of maximum cross section can be obtained by multiplying column, R, by the constant '12. For 60 m.p.h. the constant is "27. * Ihe tests on these struts were the mean of two independent experiments. , w = ratio of strength to resistance and weight on a basis of a gliding angle of 1 in 6. K40 = the above, reduced to a percentage of the highest value, i.e., for strut No. 51. Many practical conclusions can be drawn from these tests. It is evident that the radius of curvature of the run must be five or six times as great as the curvature of the entry. Cutting a piece off the bow or the stern so as to leave a flat does not seem to be very important ; in fact, stmt No. 31 has a lower resistance than strut No. 34 and the same resistance as strut No. 43. Struts Nos. 39 and 40 have the lowest resistance of all, and strut No. 40 is particularly interesting. If the run is closed in too quickly there is a fairly well-defined point at which the air no longer clings to the surface, but breaks away and forms a source of increased resistance. For example, in the series Nos. 34 to 38, strut No. 38 represents the point in question. In the 3 to 1 and 4 to 1 series much better shapes than those given can be found. The writer desires to acknowledge the great assistance rendered by Mr. V. Le Cren in preparing this report. ALEC OGILVIE. Notes on special sections.—No. 26. Section of chain tube used on Wright biplane. 24. Streamline shape, page 14. Lanchester Aero dynamics. 25. Rectangle standard for strength. 1. English Wright strut. 4. American ditto. 22. Farman strut. 23. Blcriot strut. 547
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