FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1947
1947 - 1476.PDF
240 FLIGHT SEPTEMBER 4TH, 1947 The Anglo-American Conference Vast Range of Technical Problems Examined : The Need for Research on High-speed Phenomena AMERICAN and British technicians, gathered together in London as a result of joint co-operation between the. American Institute of the Aeronautical Sciences and the Royal"• Aeronautical Society, began their three-days' session yesterday, when seven papers were read. On Tuesday, a reception was held at the R.Ae.S. headquarters, and yesterday the president of the society, Sir Frederick Handley Page, opened the session in the South Hall, Bloomsbury Square. In order to get through the nineteen lectures in three days, two are being delivered simul- taneously in the South and North Halls, an arrangement which has its drawbacks, but which was the only possible solution in the limited time available. The range of subjects treated by the different lecturers covers a vast field, and there is scarcely a technical aspect which is not covered. Mostly the papers are of a highly technical nature, and to do them justice they should be published collectively in book form. Together they would give a very good picture of the state of the art (for in spite of all the science applied to aircraft design, it is still an art) as it exists to-day. One thing which impresses one in studying the papers is the great need for extensive (and expensive) research into the many problems that have arisen as a result of the great speeds already attained and the even greater speeds foreseen. Following are summaries of six of the seven papers read yesterday. Unfortunately no copy of Dr. von Karman's paper on '' Theoretical Consideration of High-speed Flight Stability and Control" was available when we went to press. High-speed Testing By Clark B. Millikan THE full title of this paper is '' High-speed Testing in the SouthernCalifornia Co-operative Wind Tunnel " and the author is acting direc-tor of the Daniel Guggenheim Aeronauti- cal Laboratory, Californian Institute ofTechnology. In the paper the major constructional features and aerodynamiccharacteristics which make the Southern California Co-operative Wind Tunnelparticularly suitable for testing in the high subsonic speed range are described.Certain operating procedures and tech- niques have- been developed because oftheir special usefulness for such tests, and these are discussed in some detail.A device called the Lockheed "Bump," which permits data to be obtained inthe wind tunnel at a continuous series of Mach numbers near 1 are discussed,especially the effects of compressibility on blocking and other tunnel-wall correc-tions. Pertinent experimental results from a number of recent tests are pre-sented, and preliminary results of theo- retical blocking calculations for sweptwings and support struts are given. Performance in High-speed Flight By W. G. A. Perring, Director R.A.K. BEFORE dealing with the mainsubject of his paper, Mr. Perringoutlined the experimental facilities available in this country, notably thehigh-speed tunnel at Farnborough. This has a working section of ioft by 7ft,is powered by a 4,000 h.p. motor, and can be operated at pressures ranging fromnear vacuum to 4 atms. abs. The chok- ing speed (the speed of sound in theworking section) is reached when the stagnation pressure is 0.25 atmospheres. The ma.in body of Mr. Perring's paperwas devoted to an outline of compres- sibility effects on lift, drag, pitchingmoments and trim, and controls. Mr. Perring dealt next with the influ- ence of compressibility on design,dividing his examination into two main sections: flight up to sonic speed, andsupersonic flight. Under the former he referred to the need for thin symmetricalwing sections with the maximum thick- ness at 0.4 of the chord, and for fuse-lages with a minimum of cross-se.ctiorial area. When everything possible hadbeen done in that direction, further de- lay of compressibility drag could beachieved by sweeping back the wings. Unfortunately this could not avoid theconditions on the centre line, nor delay compressibility influencing the drag ofthe fuselage. Unless the aircraft were large, a fuselage would have to be pro-vided, and this not only caused drag in itself but might give rise to breakawayat the junction of wing and fuselage. In view of these drawbacks, Mr. Per-ring came to the conclusion that for subsonic aircraft we were unlikely, ex-cept in all-wing types with extreme sweepback, to delay the drag rise beyonda Mach number of 0.9. Even on all-wing types he thought it likely to be un-economic to push the speed much beyond the 0.9 figure, since to do so would in-volve extreme angles of sweepback and introduce difficult control problems. To sum up. he thought the high-speedsubsonic aircraft would have thin wings, a slender fuselage, and a 45 deg sweep-back. It might be well to consider forms of spoilers for control in roll and pitchon all-wing aircraft, or perhaps better still, spoilers or all-moving wing tips forroll and the retention of a tail but with all-moving tailplane. In considering flight at supersonicspeeds, Mr. Perring outlined the import- ance of thin wings, dealt with the effectof plan form and aspect ratio, which have a large effect on drag at Machnumbers below about 1.6 to 2, but when the Mach number reaches 2.0 the planform ceases tg be important, and the drag coefficient is almost entirely depen-dent on the thickness-chord ratio. Concerning body drag, Mr. Perringforesaw a shape of parabolic profile, with a length /diameter ratio of about 12. Thedrag coefficient of such a body would be about 0.20 and skin friction would stillaccount for about 60 per cent of the total drag. With probable figures for wing andbody drag established, Mr. Perring ex- amined the possibilities of supersonicflight. At Mach numbers of 2.0 and above, the drag coefficient of a wing of0.07 thickness/chord ratio, based on frontal area and making an allowancefor friction drag, was about 0.22. As mentioned above, the drag coefficient ofthe body "would be of the same order. This drag, the lecturer said, was barelywithin the thrust capacity of a gas tur- bine, but should be within the capacityof the ram jet or rocket. Near the speed of sound, the drag coefficient of an un-swept wing, even without any allowance for body drag, exceeded the thrust capa-city of a gas turbine when the through- put was only 12II) of air per square footof frontal area per second, a fairly con- ventional value for present-day axialturbines. It far exceeded the thrust of the practical ram jet but fell well withinthe capacity of the rocket. Mr. Perring concluded his paper withthe following summary: "In the near supersonic range one should look to thedevelopment of compact gas-turbine units with reheat and having smallfrontal area, while at speeds around Mach numbers of 2.0 and over, a combinatkmof the rocket and ram jet—the being provided to deal with the transonicregion—would appear to be the best combination." Icing Problems By Abe Silvestein THE author of this paper is one ofthe leading workers in the FlightPropulsion Research Laboratory of the American National Advisory Com-mittee for Aeronautics. His paper deals with the work that has been done ininvestigating aircraft icing problems in the major aircraft research laboratoriesin the United States and Great Britain for the past fifteen years. The funda-mental studies of Hardy and his co- workers at the Roval Aircraft E
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
