FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1953
1953 - 1285.PDF
FLIGHT, 25 September 1953 441 THE ANGLO-AMERICAN CONFERENCE The Opening Ceremony: A Varied Programme of Lectures and Discussions 'THE 1953 Anglo-American Conference was formally opened on the morning of Tuesday, September 15th, ••• in the main hall of the Friends' House, Euston Road, London. After a short welcoming address to the dele gates by Professor Lloyd Evans (on behalf of University College), Sir William Farren, president of the Royal Aeronautical Society, welcomed to London the American delegates from the Institute of the Aeronautical Sciences, and read a message to the conference from Her Majesty the Queen. In a brief speech, Mr. C. J. McCarthy (president of the I.A.S.) thanked the host society for its welcome and read messages of greeting from the President of the United States, the Secretary of the U.S. Navy and the Secretary of the U.S. Air Force. Giving details of the conference, Sir William Farren stated that a record number of over 700 delegates had enrolled, including over 150 from the U.S.A. The number of papers to be presented this year (twelve) was smaller than in the past, in order to reduce the number of days taken up by the conference (and so enable more delegates to attend), to have as few papers simultaneously presented as possible, and to give the maximum time for discussion. A provisionally arranged thirteenth paper, A Family of Delta Aeroplanes, by Mr. S. D. Da vies (chief designer of A. V. Roe) had had to be withdrawn, continued Sir William, due apparently to security reasons. The president concluded by paying a tribute to the Society's Secretary, Dr. A. M. Ballantyne, who had been responsible for a great pan of the conference organization, including the production of the excellent conference handbook. We give below, and on the following pages, summaries of the first three lectures and discussions. STRUCTURES FOR HIGH-SPEED AIRCRAFT By H. L. HIBBARD and J. F. McBREARTY (Respectively vice-president engineering and chief structures engineer, California Division, Lockheed Aircraft) MR. HIBBARD began the lecture by referring to its three sections, which dealt respectively with structural problems in high-performance aircraft, structural methods for the solution of these problems, and structural materials available for their solution. The lecturer then called attention to the imposing fraction of an aircraft's total weight that consisted of struc ture weight alone (see Fig. 1), and to the severe performance penalties resulting from relatively small increases in gross weight. The first main structural problem dealt with was that of the effects of elevated tempera tures, due both to aerodynamic heating and to thermal radiation from atomic weapons (a known probability in the future). The effects to be studied included the material's "hot" strength during and after long exposure, its weight strength after exposure, its corrosion protection and its creep properties. In addi tion, effects on the structure included distor tion of aerodynamic contour due to non-uni form heating, strength and stiffness under non-uniform heating, and overall strength and stiffness at high temperatures. A considerable amount of data was avail able so that, in general, account could be taken of the change in physical properties of the material at elevated temperatures. In spite of the range of high-quality materials avail able it remained true that at higher tempera tures, other things being equal, the structure must be heavier than would be necessary and sufficient for normal temperature environ ment. One new aspect of airframe structural design would come with the advent of nuclear- powered aircraft. It was known that many materials suffered damage, mainly with res pect to fatigue properties, when exposed to a radiation flux and many became themselves highly radioactive under the same exposure. Concerning structural design, there were four new considerations. Remotely controlled ser vice and maintenance procedures would prob ably be necessary; since large fuel loads would not be carried in the wing, there would be little bending relief there; heavy shielding for crew quarters would emphasize the requirement of dynamic vertical bending response of the fuselage; and finally, as take-off weight and landing weight would be very nearly the same, the landing gear and supporting structure would not be afforded the weight-saving that was previously available. The phenomenon of structural fatigue had become an increasingly important problem in aircraft design. This was due to the steady reduction of conservative factors in design, the increased utilization of modern aircraft in terms of service time and loading, and to the exploitation of new and stronger materials. The improved static properties of the new materials and alloys were not accompanied by a proportionate improvement in the fatigue properties. Fabrication methods which pro duced appreciable residual tension stresses were being avoided by various means to reduce fatigue difficulties, and meticulous stress analysis and fatigue testing of complete critical structures were becoming general practice. Another problem was that of structural rigidity. In the past, aircraft structures had generally been designed for specified strength levels, and the resulting stiffness had usually been adequate. Higher speeds, thinner wings, stronger materials and more refined design, however, had brought with them the need for more attention to stiffness considerations. One of the undesirable effects of flexibility was reduced aileron effectivenes due to the adverse twisting of the wing by the aileron loads, which resulted in the extreme case in aileron re versal. Another phenomenon accompanying higher speeds and more flexible structures was divergence. Additional stiffness was therefore often necessary, and resulted in the problem that, whereas in providing maximum strength for minimum weight, the stress should be every where constant and large, this did not apply in the case of design for a maximum stiffness/ weight ratio. Strength was always a require ment, but the stiffness criterion must not be overlooked. There was also an important class of phenomena involving structural flexibility where the rate of deformation with time was the significant factor. For some types of air craft, such as large transports and bombers, it was believed that these dynamic effects would become of increasing significance. The most important ingredient in a success ful design was, of course, manpower. It had been found from experience that specialized groups were required to cope effectively with the problems of aerodynamics, flutter, materials, mechanisms, etc., and the structure was no exception. In one example, the work of a specialist structures group had reduced the number of practical combinations of wing design conditions to be pursued from 2,400 to 17. The number of structural personnel should reach a peak early in the design stage, and the ratio of stress engineers to designers and draughtsmen should subsequently vary (see Fig. 2) for optimum results. The use of mechanical and electrical com puters had made practicable for routine use technical methods previously out of the ques tion due to the sheer quantity of calculations Fig. 1. (Below) Structure-weights of various types]of current aircraft. These are seen to lie between 22 and 46 per cent a.u.w. Fig. 2. (Right) Utilization of structural manpower. In this arrangement the structures personnel numbers should reach a peak before those of the design staff. , 10,000. (100.0001 1 5,000 (50000 m 100 00 ±A0 3: o •«»- i • 1 ( f » f 1 1 1 1 1 1 f 1 f 1 > 1 1 / \ \ • STRUCTU MANPOW TIME ( ^ > RES months) DESICN MANPOW •v s^. ,R A ^ ^ 5.000 (50.0001 10-000 15,000 (100,000) (150,000) DESIGN TAKE-OFF WEIGHT (lb) 20,000 (200^00) 20 0 J AHEAD RELEASE FROM PRELIM. DESIGN 8 12 T COMPLETED RELEASE OF STRUCTURES TO MFC. 16 2C 24 28 RELEASE OF FUNCTIONAL DESICN .TO MFC. FIRST FLIGHT 32 36
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
