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Aviation History
1926
1926 - 0606.PDF
SUPPLEMENT TO FLIGHT THE AIRCRAFT ENGINEER AUGUST 26, 1926 The results are better expressed as under :— oming out of a dive : R ij-r(b/c — a/c) 0-462 0-595 1-169 w In dive : ~(b/c - a/c) 0-588 ... 0-644 0-217 0-343 0-637 A comparison of these results shows that the values of km to be used require investigation, and until the correct value has been determined, the maximum load on the rear spar will remain an uncertain quantity, as also the conditions under which it arises. The values of kr given above contain the kr for the propeller as well as that of the rest of the aeroplane, and the limiting velocity is worked out with this value. Analytical investigation has shown that the maximum load on the wings in coming out of a dive is reached very soon, and that by this time the velocity has changed but slightly. Owing to the velocity being slightly less than the limiting velocity, the error in taking the moment round the wings, the same as if in steady flight, is diminished. So far a comparison has been made between the loads on the rear spar in a vertical nose-dive with terminal velocity and in coming out of a dive. The maximum load on the wings in the latter case is taken as the weight of the aeroplane. "" W," multiplied by the load factor " n," and no factor of safety '' / " has been taken for the other case. The work will now be recast with the factors of safety 1-25 and 1-75, so that the maximum load on the wings is n WT, and the consequent load on the spar will then be multi- plied by "/." For the nose dive case the load on the spar obtained in the previous work will simply have to be multiplied by F. The figures for km will be taken as in R.R. 81 :— P. 7 (o) Full scale R. & M. 400 (6) Model R. & M. 440 (c) Model aeroplane T. 709 (d) Full scale, no stagger Factor of Safety = 1 • 25 = /. A. B. 0-140 0-171 for Lift = «,W — km h R! (b — a) c.«].W R 0-0365 0-261 0 0471 0-275 rl rl rl vl,s»//. c. 0 139 0-0490 0-353 500 25 10 500 D. 0-140 0-0389 0-278 0-137 0-151 0-228 0-154 -a/c) 0-75 0-83 1-25 0-85 In dive : R ^-(b/c-a/c) 0-75 0-44 0-38 0-71 P. 9. h 0-164 0-204 0-163 0-164 for lift = n,W - km ...0 0400 0-0531 0-0555 0-0429 kc 0-244 0-260 0-340 0-262 R, (b - a) cn yr~ 0085 0-101 0181 0103 R ^rr(b/c — a C) In dive : ... 0-60 0-71 1-27 0-72 ^- b/c-aic) 0-80 0-27 0-43 0-80 Factor of Safety f = 1 • 75. w, = n/f. P- "'• A. B. C. D. &L 0100 0122 0099 0100 for lift = re,W — k.„ ...0-0310 0-0380 0-0379 0-0325 kc 0-310 R, (b — a) c.n,W ^-(b/c - a/c) In dive : yy(b/c - a/c) ... 0186 ... 1-02 0-311 0-381 0-187 0-257 0-325 0-201 1-03 1-41 1-11 ... 1-05 0-61 0-53 0-99 P. 9. kL 0-117 0-146 0-117 0117 - km 00334 0-0426 0-0430 0-0351 kc 0-286 0-292 0-368 0-300 R, (b — a) cnW 0-127 0133 0-209 0-141 R ^(fe/c-e/c) 0-89 0-93 1-46 0-99 In dive : R ^-(b/c-a/c) ...1-12 0-38 0-60 1-12 R With the notation above, — (b/c — a/c) is given aa under. Coming out of a dive. P. 7. Factor of Full Model Model No Safetv Scale rl = 25 vl — 10 Stagger A. B. C. D. P. 7 1-0 0-62 0-69 1-17 0-72 1-25 0-75 0-83 1-25 0-85 1-75 102 1-03 1-41 111 P. 9 1-0 0-46 0-60 1-17 0-59 1-25 0-60 0-71 1-27 0-72 1-75 0-89 0-93 1-46 0-99 In Dive.— P. 7 1-0 0-60 0-35 0-30 0-57 1-25 0-75 0-44 0-38 0-71 1-75 1-05 0-61 0-53 0-99 P. 9 1-0 0-64 0-22 0-34 0-64 1-25 0-80 0-27 0-43 0-80 1-75 1-12 0-38 0-60 1-12 Some interesting experimental effects with regard to the orders of acceleration which might be expected in flight have been published in the Reports of the National Advisory Committee for Aeronautics (U.S.A.), 1924. The following table is abstracted from Report No. 203 :— Power spirals ... ... (sustained) 4-7 g. (Pilot experienced loss of sight.) Maximum ... ... ... ... ... 5 • 5 g. Immelman turn ... ... ... ... 4 • 4 g. Vertical bank ... ... ... ... 5-7 g. Loop start 3-2 g. Upside down flight ... ... ... ... — 1 • 2 g. Recovering from loop ... ... ... 4-2 g. Spin ... " 2-6g. Low flying in rough air over mountains ... 2 g. Rough air from convection currents 2-2 to —0-5"g. In the ease of pulling out of a dive experimental observa- tions are given in the following table, and compare with the theoretical calculations :— Air Speed. Acceleration Acceleration M.p.h. (Experimental). (Calculated). 66-3 1-3 1-35 76-0 1-6 1-78 85-6 2 1 3-25 95-3 2-7 2-79 105-0 3-3 3-40 114-5 3-9 4-04 1240 4-6 4-74 133-6 5-3 5-50 143-3 6-1 6-32 153-0 6-4 (low) 7-22 162-5 7-8 8-15 It will be noticed that very high experimental accelerations have been measured, figures considerably in excess of those which in previous opinion a human being was capable of sustaining without loss of consciousness. The following quotation dealing with the physical sensa- tions of the pilot is particularly interesting. '" From the results of these tests, it is apparent that serious physical disorders do not result from extremely high accelerations of very short duration, but that accelerations of the order of
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