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Aviation History
1939
1939 - 0077.PDF
JANUARY 12, 1939 FLIGHT. a GORDON AEROUTE: f Fig. i. "Cord ''' material ol two years ago compared with modern "Gordon Aerolite,' which is almost twice as strong and three times as stiff. PLASTIC PROGRESS Some Further Developments in the Manufacture and Use of Synthetic Materials for Aircraft Construction By N. A. de BRUYNE, M.A., Ph.D IT is almost two years since I had the privilege of talking to the Royal Aero nautical Society on the subject of plastic materials for aircraft construc tion.* Since that time a good deal of progress has been made, and the nature of the problems facing us has rather changed. We were then concerned with the improvement ol the mechanical pro perties of the material in order to make them comparable with those of wood and metal. No problem of that kind can ever be said to be completely solved, but we are satisfied that we can now produce a synthetic material with properties which are good enough for aircraft con struction and which in some respects (such as tensile strength and Young's Modulus) are better than those of other materials. Our problems now are those of the production and of the utilisation of the particular kind of material which we have developed. I shall confine myself here to the reinforced type of syn thetic resin material, and shall not deal with what are known as "improved woods." Though I am keenly in terested in these materials, I cannot claim myself to have had any considerable first-hand experience of them. Two years ago the best material that we could produce was known as "Cord " material. Fig. 1 gives a pictorial representation of the improvement that has since been made by the substitution of, inter alia, linen for cotton reinforcement. This type of reinforcement was suggested by Mr. Malcolm Gordon as a result of the publication of my previous lecture. I only hope that this talk may have some such equally far-reaching and satisfactory result. Fig. 2 gives numerical data and is followed by a table * Journal ol the Roycu Aeronautical Society, XLI, p. 523 (1937). rTHE author is director of the Aero Research Laboratories at Duxford. and has spew much time on developing synthetic resin ma terials for aircraft purposes. Some indication of the progress made since he read his now-famouf paper before the Royal Aeronau tical Society is provided in this summary of the lecture given by him to 'he Weybridge Branch of the R.Ae.S. last week. At least as interesting as the improvement in the materials themselves is the very ingenious joint which Dr. de Bruyne has introduced, and which he describes (Fig. 3) which enables a comparison to be made between various materials on a strength-to-weight basis. I think it may be said that, in so far as such comparisons have significance, " Gordon Aerolite " compares very well with that of materials at present in use in aircraft construction. The impact figures obtained and the type of impact fracture observed are satisfactory. An impact specimen which has been subjected to the standard im pact test for spruce, according to Inspec tion Leaflet 7 of A.P. 1208 (the figure of 12 ft./lb. is our specification figure), shows a type of failure which is not that characteristic of a brittle material, although the stress strain diagram of "Gordon Aerolite" is linear, that is to say, obeys Hook's Law, right up to the point of fracture. So much for the material ; now lor a brief account ot its production. To secure uni formity and keep to the specification figures it is, of course, essential to maintain a constant control over the process and make tests at every stage of production. The first step in the process is to get all the fibres uniformly arranged parallel to one another. This is done by a special machine which is shown in Fig. 4. This machine takes in loose fibres, draws them into a uniform band, and then passes this band through the impregnating bath, after which it is dried and is ready for pressing. The whole process of impregnation is an extremely interesting one ; too great an impregnation leads to a swelling of the fibre, with reduction in strength ; too little impregnation leads to a poor shear strength and poor machining properties The dried and impregnated (but not yet polymerised) Material. Ci*d Material Gordon Aerolite ... Duralumin Spruce Steel t Tensile Strength. Ibs./in.1 25,000 45,000 55,000 10,0011 180,000 c Coma. Strength. Ibs./in.' 27,000 24,000 55,000 5,000 180,000 H Young's Modulut. Ibs./in.2 2.4x10* 15.0 x 10* 10.0X10* 1.3x10* 30.0x10* s Shear Strength. Ibs./in.* 5,800 5,000 30,000 750 106,000 P Specific Gravity. 1.34 1.43 2.8 0.5 7.8 Material. Cord Material Gordon Aerolite Duralumin Spruce Steel t/P ibs./in.* 18,700 31,500 19,700 20,000 23,100 C/p lbs./in.a 20,161' 16,800 19,700 10,000 23,100 E/p Ibs./in.' 1.79x10* 4.20x10* 3.57 X 10* 2.60 X 10* 3.85x10* S/p lbs./in.« 4,330 3,490 10,700 1,500 13,500 Fig. 2. Physical characteristics of various materials. Fig. 3. A comparison between various materials on a strength-to-weight basis.
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