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Aviation History
1936
1936 - 0185.PDF
January 23, 1936 Supplement to m @J^CT (?$®z FLIGHT ENGINEERING SECTION » nn /Volume XII\ ,,..,. „_„ No. 120 ^ No j J 11th Year January 23, 1936 STALLING of TAPERED WINGS A Reply to Dr. LachmanrCs Recent Article in "Flight" By W. R. ANDREWS, A.F.R.Ae.S. IN an article which appeared in Flight of J anuary 2 under the above title, Dr. G. V. Lachmann gave theoretical reasons to show why a tapered wing stalls first at the tip instead of at the root as in the case of a parallel wing. Except that the wings he considers are tapered in plan form and are without aerodynamic twist, no limitation is given as to the aerofoil section along the span. From a study of his conclusions, it is obvious that he has con sidered only wings having the same aerofoil section along the span, that is to say, the relationship between thickness and chord is the same at any section. This undefined limitation is the reason for the conclusions at which he has arrived, as will be demonstrated later. This limitation is hardly in accord with almost universal practice so far as cantilever wings are concerned. It may be true for certain biplane arrangements or nearly so for wings with MAXIMUM LIFT DISTRIBUTION ALONG THE SPAN FOR. DIFFERENT NO-LIFT MOMENTS I ^produced from Mr. Andrews' article on "The Design of Aerofoils and the Prediction of Characteristics," The Aim-nft Engineer, December 28, 1933. The Aircraft elliptical plan forms, where the thickness ratio is more or less constant along the span. In practice, the more general method of designing wings is to adopt a straight taper, at any rate for the outer portions, and to employ a thickness—chord ratio of about 18 to 20 per cent, at the root, tapering to 9 or 10 per cent, at the tip. The amount of taper in plan (expressed as tip chord — root chord) seems to be from A = 0.45 to A = 0.6 and for the purposes of illustration tapers of 0.75 and 0.5 have been assumed combined with t = .18 at the root tapering linearly to .09 at the tip. These arbitrary cases have been chosen because the loading curves are given in A.P.970 and by coincidence the case of A = 0.5 roughly represents current practice for cantilever mono planes. It has been demonstrated in a previous article ("The Design of Aerofoils and the Prediction of Characteristics " —The Aircraft Engineer, November 30 and December 28, T933) that the maximum lift of a wing varies with (a) The
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