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Aviation History
1932
1932 - 0765.PDF
JULY 29, 1932 55 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT The rolls can then be built up round them, care being taken to back up the metal, as shown in Fig. 5, to prevent reverse bending. Some register must be provided to key together the upper and lower rolls of each pair. The working sur faces themselves will sometimes automatically do this, but generally it is necessary to have flanges on one or other of the rolls. These may be integral with the rolls or may consist of discs assembled with the rolls on the spindles—see Fig. 5. In order to minimise friction, wear of rolls and unnecessary working of the strip, the rolls should be designed to touch the metal only where it is absolutely essential. For this reason and to save machining cost, it is usually advisable to allow only nominal radii in re-entrant corners on the rolls—the work being done on the male portion at these points; nothing is gained by having the metal restrained on both its sides (see Fig. 5). Another important point to be considered is the pro vision of a good lead-in, both to ease the metal round gradually and to prevent the rolls scoring or chafing it. To this end generous radii and open angles on the parts that touch the material first should be provided, as shown in Fig. 5. For the same reasons, vertical walls should not be produced completely in one pair of rolls unless they are very small. To economise in initial work and subsequently in set ting up time, it is often desirable to cater for more than one thickness of strip when designing the rolls. In such cases the thickest material to be considered should be taken as the basis of calculations and rolls should never be called upon to deal with any strip more than 20 per cent, thinner if accurate results are required. (To be continued.) TORSION CALCULATIONS FOR A REAR FUSELAGE WITH TWO OR MORE " UNKNOWNS." By H. DAVIES, B.A., A.F.R.Ae.S. I SHOULD like in the following remarks to refer again briefly to the above problem, which was dealt with in last month's issue of THE AIRCRAFT ENGINEER. Attention is directed to the attached diagrams 3 and 4. These figures show the load system applied to the aftermost bulkhead of the rear fuselage, in terms of two unknown reactions at the stern end. Fig. 3 applies to the conventional way of treating the rear fuselage, and shows the load system in terms of two unknown reactions, x and y at the stern end of the fuselage. Fig. 4 applies to the proposed new method of treatment. Here x and y are grouped together and replaced by a single variable u, where u = x + \j. Fig. 4 shows the load system applied to bulkhead CcdD in terms of the two new unknowns, x and u. It will be observed at once that u has the dominating influence on the rear fuselage, while the effect of x ;.s to apply a small correction. This condition should be contrasted with the load system of Fig. 3, where x and y are seen to have an approximately equal influence on the rear fuselage structure. In the previous article, appearing in the June issue of THE AIRCRAFT ENGINEER, complete strain energy cal culations were given for the rear fuselage in terms of the new variables x and u. The final resultant equations— which were readily soluble—were as follows: (1) 4,323a; 7,360M - 40-83 X 10° = 0 or 0-587a; 4- u — 5,550 = 0 (2) 7,360* + 301,430M -684-1 x 10« = 0 or 0-024a;+ u -2,270 =0 These give : x = 5,830 lbs. u = — 2,130 lbs. ( = x + y) y = - 3,700 lbs. For purposes of comparison, strain energy calcula tions on the same rear frame have been carried out in terms of x and y (Table 5 of the previous article gave a specimen of these calculations for the top longerons; the remainder of the calculations were not included). The final resultant equations in terms of x and y are as follows : (3) 320,890a; + 308,900;/ - 725-5 X 106 = 0 or 1-040.T + y -2,348 =0 (4) 308,900a; + 301.430?/ - 684-1 x 106 = 0 or l-025a; + y -2,269 =0 These equations give a crude solution which is in reasonable agreement with that obtained above; but the equations are far too similar to make any accurate solution possible. ERRATA. ATTENTION is drawn to two mistakes which occurred in Mr. Davies' article last month: — In Fig. 4, on p. 46. " 1.50w " should have read " 1.50x." On p. 48, in the table " Summary of Strain-Energy Calculations," the figures in the middle column of the table, for side wires, should have read " 714x — 6,420«," and not as printed 714x + 6,420K. Will readers who wish to have their copies accurate please make the necessary corrections. 710^
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