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Aviation History
1932
1932 - 0101.PDF
JANUARY 29, 1932 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT limits, allowing ample clearance in the female portions of the auxiliary hinges to cover discrepancies in hinge centres. Suitable limits for hinges are given in Table V, which warrants a little further discussion. MASTER AUXILIARY W + -0OI* 7+ .005 Y --00I" * -005 ' . - 1 z F1G.2 L± 030* "* * > . --001*1, c - 005 R. RODGER Consider the pair of hinges—master and auxiliary— shown in Fig. 2. The dimension Z must be sufficient to cater for: — (i) The tolerance in the master hinge, (ii) The tolerance on the hinge centres, (iii) The maximum thickness of the male portion of the auxiliary hinge, (iv) A reserve clearance, say 0.001 in. Thus, the tolerance on Z = Y must be 0.010 + 0.060 - 0.001 + 0.001 = 0.070 in. +0.070 Hence, the minimum size for Z must be Y _Q Q in. In practice it is usual to exceed this tolerance and give ample clearance. MASTER FIG.3 AUXILIARY AUXILIARY AUXILIARY M U CORRECT INCORRECT L + -03 Lt-03* •03 Lt-03 L±-30 L*-03" In order to avoid duplication of tolerances all hinge centres should be referred to a common datum—the master hinge—as shown in Fig. 3. This practice should, in fact, be made general for all classes of work where duplication of tolerances may arise. Plate Fittings The limits of error on the general dimensions of the profile of sheet metal fittings where intercliangeability is not involved should be within nominal size and plus ff's in. The thickness of sheet metal used for small fittings such as wiring lugs, etc., should not differ from the specified nominal thickness by more than the amounts quoted in column 2 of Table VI. For large sheets over 3 ft. wide to be used for pressings, etc., the tolerances may be increased to the values quoted in column 3 of the table. The stock delivered from the rolling mills is fairly consistent as regards thickness within the limits stated, but, nevertheless, the practice of " weeding " sheet metal is to be recommended. Thick sheets should be set aside for the manufacture of fittings involving welding as a production process, the resultant scaling and reduc tion in gauge thus being offset to some extent. Several years ago the writer conducted a series of TABLE VI. Sheet. Mela!. Imperial L S.W.G. 6 8 10 12 14 16 18 20 22 24 26 Small Sheets 3 Ft. and Under. On Nominal Thickness. -0. + 0012 + 0-012 + 0-010 + 0-010 + 0-006 + 0-006 + 0-006 + 0-005 + 0-005 + 0-003 + 0-003 Large Sheets over 3 Ft. Wide. On Nominal Thickness. - 0. + 0-014 + 0-014 + 0-012 + 0-012 + 0-008 + 0-008 + 0-008 + 0-007 + 0007 + 0-005 + 0-005 Bend Radii. Low- Tensile Steel. * i A SI A A -±- A A A i 35 H.T. Steel and Dural. , * i * S A A 4 A A A experiments to determine the most suitable bend radii and allowances for different gauges and materials, samples of S.3, S.4 and L.3 being utilised. From the results, the inside radii for bends wore graded to linear laws according to gauge of plate and nature of material, the following expressions being derived therefrom:—• (i) For Low Tensile Steel. R = 1.9T - 0.0-5 with low limit, R = 0.03 in. for T < 20 S.W.G. (ii) For High Tensile Steel and Duralumin. R = 2.IT - 0.025 with low limit, R = 0.03 in. for T < 24 S.W.G. where R = inside radius of bend, in inches, and T = nominal thickness of plate, in inches. The bend radii quoted in Table VI are calculated from these formula?, but for practical reasons are given to the nearest A in- With these bend radii, the bending allowance may be expressed as a function of the bend angle and the plate thickness, irrespective of material, thus: BA = (6.3R + 2.5T) 360 v where BA = bending allowance, in inches, 6 = angle of bend, in degrees, and R and T are as before. The should Tubing profile of round external profil d and square tubing be within the limits stated in Table VII. The TABLE VII. Tubing. Profile of Round or Square Tubing. Diameter or Flats. In. Up to 1J i*-a 2£-2i 3^-34 3TM 4TV5 Limits. ± 0-003 ± 0-004 ±0-005 ±0-006 ±0-007 ± 0-008 ±0-009 ±0-010 Wall Thickness All Tubing. S.W.G. 10 12 14 16 17 18 20 22 24 26 Limits. ±0013 ±0-013 ±0-009 4- 0-007 ±0-006 ±0006 ±0005 ±0-004 ± 0-003 ±0-003 96 c
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