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Aviation History
1933
1933 - 0859.PDF
October 26, 1933 Supplement to FLIGHT Edited by C. M. POULSEN October 26, 1933 CONTENTS The Design of Aerofoils and the Prediction of Characteristics. W. R. Andrews, A.F.R.Ae.S Tool Room Tempering Equipment In the Drawing Office— Strength of Tubes. By K. Parkinson Airwork Engine Service Technical Literature— Marine Aircraft Design .. .. ..' .Summaries of Aeronautical Research Committee Reports .. By Page 69 71 7:; THE DESIGN OF AEROFOILS AND THE PREDICTION OF CHARACTERISTICS By W. R. ANDREWS, A.F.R.Ae.S. Mr. Andrews, who has contributed numerous articles to THE AIRCRAFT ENGINEER, is on the Technical Staff of A. V. Boe & Co., Ltd. He has been working on this article for something like a year, and has had to '' scrap " large sections and start afresh on a new line of attack. We think it will be agreed that in the final presentation his method is as simple as such a complicated subject will allow.—ED. IN the design of aerofoils and the analysis of their characteristics, it has been customary to use as datum the line passing through the centres of radii of leading and trailing edges (Ref. 1). The definition of camber has been the " rise " of the mid point between upper •ind lower surfaces when measured normal to the datum. In a previous article (Ref. 2) curves for the estima tion of profile drag were given in terms of the maximum camber, based on the above definition. These curves •we obtained from the N.A.C.A. variable-density wind- tunnel test on series 00, 43-63 and 45-65 (Refs. 3, 4 and 5). Since their publication, the test results of another Pi'ies of aerofoils (Ref. 6) have been published. This ones has the maximum camber at 40 per cent, of the nord and two camber ratios 4 per cent, and 6 per cent. ™mbined with thickness ratios of from 6 per cent, to ' per cent, of the chord. These tests give results on actions midway between series 43-63 and 45-65. All • nese aerofoils are numbered to define the principal reonietric characteristics. The first figure gives the 'tiiximum camber off the section as a percentage of the 1 |)o>d, The second figure gives the position along the 'lord at which the camber is a maximum. This is '^pressed as percentage +10. The last two figures 'n'e the maximum thickness as a percentage of the chord. Thus section No. 6406 has a 6 per cent, camber at 40 per cent, of the chord, and the maximum thick ness of the section is 6 per cent., and so on. The geometrical construction of these N.A.C.A. aero foils is also somewhat different from that previously used. Instead of the profile being draped round the centre line by taking ordinates normal to the chord, the ordinates are set out normal to the centre line itself (see Fig. I). This method of construction makes the analysis of existing aerofoils a little more complicated, but the test results so far obtained seem to justify its adoption for general use. TANGENT TO <£ AT CENTRE OF LE RADIUS LE RADIUS LE. It is found that a piece of celluloid marked out as Fig. 2, and having a small hole into which a pricker can be inserted at the mid point, provides an easy means' of obtaining the centre line of an existing aero foil. The celluloid is moved about until line "A" cuts upper and lower surfaces at equal angles, and the mid point " B " is half way between the two sur- CELLULOID SHEET \ ^ \ -'^^V^ \ z5 S\ ^^Ao^j ^3g -^\<^^\ "\ FI6.2. \ <t CARRIED THROUGH \ BY EYE -^/ <bJ\~~~>^ POINTS PREVIOUSLY J^y^ \ ""//\ OBTAINED <^V \ ~" - ^ \ **^^ \ '—~~~—-^ " \ - *£ ^ ^-^^ ^""~~^~-^^\ EQUALLY SPACED PARALLEL LINES 1072 a r>2
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