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Aviation History
1926
1926 - 0123.PDF
17 FEBRUARY 25, 1926 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT + 0-4-1 ( 1-167* X (0-766 + 0-985) 1-082 0-42 \ 150 1 0-42 2 X 1-167 x 0-4 0-12\ 100 (0-985 -0-342) 1-08 x 0-1 X 0-985 X 0-342 + 2-1755 - 0.18 X 0-9812 01837 + 01735 4 = 0-251 - = 2 • 7827 I flange = 2-7827 X 4 x 0-22 = 0 245 in.4. 1 web =0-1 X 1-0572 r9o n + 0-9612 X C-18 (0-858 Jo ,-0-858 0-1 cos 0)2O1 dB -0-85 /-9O + \xidx+ (0-658-0-2 cos <9)2O-2</<9 . 0658 . 20 (•70 + (0-5 cos 6)1 0'5 do j o 0-35 + 0-166 - ()•] I (0-8582 0-1- "> 90•3 2X 0-858x0-1 v 0-2 j"(o- 1 658* + —\ — -2 x 0-658 2 / 57 •3 X 0-2 (1 - 0-342) - °— x 0-64214 J 2 x 57-3 y 0-643 ]J = 0-35 + 0-166 + 134 ~ 0116 -f- 0075 — 0097 = 0-938 I web = 0-938 x 4 X 0-018 = 0068 in.1 Total I of spar = 0-245 — 0068 = 0-313 in.4 By Webb and Thome's formula for Max. Bending moment we have :— Euler Load Q = TT 2EI IT- X 30 x 10c X 0-313 ~F~ = 30 x 30 = 102800 M (max) = -^—- -j ^ (MA + MB) Fl + 0-26 ? L0^.|o.5(1900).l+026x ^?»-)97800 l '\ ' 1C2300/ +- 1-02 v ]2J x 0-5 X (HOP) 2 8 |+ 121) = 1,918 ft. lbs. 2-52 ,. . 12 Mv V 12x1,918x1-575 f 5,000 (max.) = + — = ' A : ; I A 0-313 0-2578 = 115700 + 19400 = 135100 Ibs./sq.inch. Therefore, this spar will be O.K. in DTD 16/50 steel. We will now get out the rolls or dies for making the sections out of flat sheet. These must be made very accurately, for if the strip is gripped tighter in one place than another it will come out twisted. The first rolls are got out by sight from experience ; the last but one is generally made of similar dimensions to the finished section and the last has to be such that the spring back will give the correct section, and is arrived at in the following manner: E fWe know that - = —. R y If we denote the finished section constants by Ex Rx/i and y1 and those of the section in the last die bvE2 R, /.2 and yi "V Y f f we rrg*. JJ: _ __ l _ lL _ ±1, but/j = 0, as there is no stress D R 2 Rt y2 y1in the metal after spring back and / 2 = yield stress, as thematerial yields in the die to give it its new curvature. This is not the yield stress from specification, but from test of material used, and is about 70 tons/sq. inch in DTD 16/50. ~EX = E, and y± = ?/,. /I 1 x LWe can therefore write E — I = '— ,1 If,and — — — = —. R2 Rl Ey We will work out the last die for the flange. Let us denote the arc of • 15" radius by 'a,' -4 by ' b,' and -1 by ' c ' lib Re 70 13,600 X 2-137 2-137 0- 0- 1 0- Oil 4 1 0- 0- 1 015 3365 0957 2-137 H5 0-1395 This gives our radii for the last die as -1395", -3365" and •0957" respectively. Now the length of arc of each separate curve must remain the same for all the rolls and dies. Therefore the new angles will be , > 0-15 X 50 01395 = 53-7°. (6) °-4^150= 178-7°. (c) 0 3365 0-1 X 100 0-0957~ = 104-3°. Fig. 5 shows the rolls and dies. The first two may be rolls but the last two must be dies ; the distance x being less than y the rolls could not run in each other. Xo. 3 could be made suitable for rolls by cutting away the small portion that fouls. This being so small would not harm the strip. The axes of the male and female rolls should be equi- distant from the centre of the strip x — x ; this minimises the amount of slip caused by the difference in linear velocity of the rolls, which increased with their difference of diameter at any point. The rolls for the webs may be found in the same way ; it will be better to have five instead of four for this section. Some firms have fitted a furnace to their drawbench and they draw the metal hot. I have no experience of results, but would imagine that the dies would be difficult to design, the yield point being an unknown quantity. Against this method is the very much greater time taken. W'ith good tools and a little experience, good results should be got from drawing cold. Twist is often due to badly made dies or drawing through two at once that arc not in line. It is better to have the rolls sliding on a splined shaft ; if they are fixed it is very difficult to get three or four dead in line. Always have a lead in on the dies. Make, say, J in. of the die the true section and chamfer the rest off. A test should be made of all new spars to see that they develop the. required stress without local buckle. The Editor will be •pleased to receive for consideration articles dealing with constructional and designing problems. All articles accepted will be paid for at our usual rates. WOe
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