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Aviation History
1931
1931 - 0394.PDF
SUPPLEMENT TO FLIGHT 32 THE AIRCRAFT ENGINEER APRIL 24, 1931 •+• F/G.JF. /?/& O/?0MT£S. f r •Si, /7^ 3Y5 ?/7 X i'7 y •51 05 •0 01 % /4i t:V A \K •50 La Ifo in 121 aa) 25-3 a» _K. »(5 (!S? W-4 2/5 /V 7 •Ml-51 *S& Hi Hi •e/fl * -/a- 1 k• • »" The idea was taken from a treatise on yacht's lines, where the author of the treatise had based his assumption on the fact that a yacht's lines are of parabolic form, and he used A/fc2the well-known formula for a parabola a = —. All the offsets for the lines were calculated and issued to the mould loft without a single lines drawing having been issued. The advantage gained is not the subject of this article. In a " wash out" wing tip, the top and bottom surfaces Ah?usually conform to a parabola, and the formula a = —- could be altered to 3uit the working out of the ordinates for the taper ribs by expressing same thus :— / *a = The writer had occasion to require the true shape of a section of the wing tip at " XX," known as a " cant" in shipbuilding, and although the layout for the taper ribs was correct in profile, it was found on " lifting " the " cant," that the new shape was 0-1 inch out in height. Thh was, no doubt, due to the fact that the ribs were not faired in all three views. As the new rib was in metal, it was necessary that this should be correct in profile, and by applying the formula already mentioned, it was possible to get the correct outline for the taper ribs, and hence the new rib at " XX," Fig. IV. Fig. I. is a profile of the last normal rib marked L.N.R. in Fig. IV. In the table of ordinates, Fig. Ill, the ordinatee for the L.N.R. are marked X and Y, being top and bottom ordinateB respectively, above datum. Let d equal the diameter of the wing tip tube, K the distance of L.N.R. from wing tip tube, centre to centre, A = , Fig. II, and k the distance from L.N.R. to taper ribs, 1, 2 and 3. x and y are top and bottom ordinates of taper ribs above datum, see Fig. II. x = X — a and y = Y + a. In the example marked in Fig. Ill, d was taken at 0-75 inch diameter. K In the eighth column from the left we get —7=, and this V7A remains constant throughout the rest of the working, the only variable being 1c. Values of a can easily be worked on the slide-rule, watching the decimal point in doing so. There may be two or three taper nose ribs between each full taper rib and a column for these can be inserted in the correct place, if necessary. In Fig. V, the nose of L.N.R. and the first taper rib have been laid out from the tables in Fig. Ill, from the L.E. to the front spar only, and the rib flange centre is shown running into the centre of the L.E. tube, the hatched portion showing the fabric leaving the rib to pass over the L.E. tube. The top and bottom flanges of the rib can, of course, be run in tangential to the L.E. tube, and is a matter of choice of attachment of ribs to L.E. tube. In laying out the wing tip in plan, the writer has shown radii in terms of " C," the chord, trusting same will be useful to junior draughtsmen when laying out a round wing tip. The form obtained will be found to give good results aerodynamically. All ordinates are above datum, and the datum in Fig. II has been purposely/ shown much lower than is found in practice to show up a and y more clearly, but is truly repre- sented in Fig. L Owing to lack of space, the summaries of Aeronautical Research Committee Reports and Memoranda which usually appear in the last part of THE AJKORAIT ENGINBBB have had to be held over this month. It is hoped to publish a lengthy series of them in (he May issue.—ED. 362A
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