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Aviation History
1934
1934 - 1436.PDF
SUPPLEMENT TO FLIGHT 48 JUNE 21, 1934 THE AIRCRAFT ENGINEER IN THE DRAWING OFFICE MONOPLANE WING LAYOUT BY H. H. HUTCHISON. THE ensuing method of laying out a monoplane wing is applicable particularly where it may be found necessary for reasons of expediency to vary the proportionality of the rib contours. In other words, the locus of the C.P. is made to depart from the conventional path, as in the case of a normal two-spar wing. In the case I am dealing with two spars are shown, but, of course, the method of laying out applies equally as well for a monospar. The wing dealt with is straight in front elevation from left-hand wing tip, along the tops of the ribs to right-hand wing tip. Fig. 1 is an outline in plan indicating the rib spac- ing. If the positions of the spars are already fixed up, dimensions for the nose and trailing edge can be given from these, otherwise a datum line is necessary. The dimensions for the chord, nose to centre line of front spar and trailing edge to centre line of rear spar can be found readily from Fig. 1 by calculation, or by the following graphical method. For simplicity sake it is assumed that the rib spac- ing is 12 in., and that the spar axes are parallel in plan view. Draw a horizontal line representing the spar centre lines coincident. Draw parallel lines to represent the ribs perpendicular to this line at 1 in- apart. At line 1 measure up, full size, dimension " b " from Fig. 1 above the horizontal line, this being the amount "the nose is ahead of the front spar at rib 1. Below the horizontal line measure off dimension " C," again at line 1, i.e., the amount the trailing edge is behind the rear spar at rib 1. Proceed in the same way at line 15, using dimension " a " above, and " e " below, Fig. 1. By joining these points all the other rib lengths + the constant can be measured off full size, due allowance to be made at the end ribs when detailing for the wing- tip curve. Having decided the wing section, superpose in end elevation the rib contour of the smallest rib, neglecting end ribs, on the rib contour of the largest rib, placing the chord lines at that distance apart required to give the correct dihedral, dimension " x," Figs. 3 and 4. Next mark off on the chord lines 0.0125, 0.025, 0.05, 0.075, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90 and 0.95 of the respective chords and draw perpen- dicular lines, cutting the contour. Scale these vertical dimensions, enter them in a table, and prepare a series of foreshortened views—one of which is Fig. 4—in order to use the dimensions thus foimd. -1 -075 05 •025 •0125 e> _»-—•— •0125 )• ' •025 j- 1 •as i-^g•075 t=?= I fT.r •— , 1 __- • *^= 1 j 11 I —HpzJ : fc=2 1 •—J .i i —— —-• —- _- s I _—— 9 i 1 1 A O 1 \ * tX FI6.4 " 1 . •• 1 | 1 Start by drawing twelve vertical lines 1 in. apart, Fig. 4, and a horizontal line across them. From the horizontal line measure up line " 12 " full scale the amount the small rib chord line is above the large rib chord line, dimension " x," Figs. 3 and 4. Join this point to the point of intersection of line 1 and the horizontal lime. The intersections of this sloped line with the vertical lines are therefore the chord lines of all the other ribs between "1" and "12." Above and below points " A " and " B " measure off full size the dimensions of the ordinates of the con- tour of ribs " 1 " and " 12 " at the various stations, i.e., 0.0125, 0.025, etc., taken from Fig. 3, and join up. Thus the ordinates of the contour of all the other ribs may be scaled off full soale each from its respective chord line, i.e., the point at which the line A-B inter- sects the rib lines. A similar diagram to that of Fig. 4 can be further used to lay in the axes of the spars in front elevation, for by this means the relative position of the rib chord line and spar centre line at any rib can be measured off straight away full size. And so with the hinge centre line of the aileron. Select a rib, say 9, and fix the centre line of the inner hinge upon it. From this point draw a straight line to the extreme tip. Again the relative positions of the hinge centre line, chord line, and spar centre at each rib is obtainable to full size scale, no matter how big the wing span. Mention, of the extreme wing tip calls for a brief word upon fairing off the wing tip from rib 12 outwards. A compromise is necessary as a rule. The chord lengths of ribs 13 and 14 are definitely fixed in Fig. 1 in order to obtain the good end curve. Thus a fair curve in end elevation, Fig. 3, allied with a reasonable curve in Fig. 4 (extended), using the rib lengths of 13 and 14 chords, correctly spaced as regards other ribs in plan, but not so in end elevation necessarily, is a practical solution of the problem. 608 h
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