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Aviation History
1954
1954 - 0435.PDF
and AIRCRAFT ENGINEER First Aeronautical Weekly in the World Founded 1909 No. 2352 Vol. 65. FRIDAY, 19 FEBRUARY 1954 EDITOR MAURICE A. SMITH, D.F.C. ASSISTANT EDITOR H. F. KING, M.B.E. ART EDITOR JOHN YOXALL Editorial, Advertising and Publishing Offices: DORSET HOUSE, STAMFORD STREET, LONDON, S.E.1. Telegrams, Fiightpres, Sedist, London. Telephone, Waterloo 3333 (60 lines). Branch Offices: COVENTRY 8-10, Corporation Street. Telegrams, Autocar, Coventry. Telephone, Coventry 5210. BIRMINGHAM, 2 King Edward House, New Street. Telegrams, Autopress, Birmingham. Telephone, Midland 7191 (7 lines). MANCHESTER, 3 260, Deansgate. Telegrams, IlifTe, Manchester. Telephone, Blaekfriars 4412 (3 lines) Deansgate 3595 (2 lines). GLASGOW, C.2 26b Renfield Street. Telegrams, lliffe, Glasgow. Telephone, Central 1265 (2 lines). SUBSCRIPTION RATES Home and Overseas: Twelve months tJ3s.0d. U.S.A. and Canada, $10.00. BY AIR: To Canada and U.S.A., six months, $16. *N THIS ISSUE : Archeology from the Air 200 B«aver in Mexico - - 203 A"ialysing the Beverley - 205 s-a Hawks 209 Attracting the Airline Pilot - - - 216 High-speed Terminology SHOP TALK in most industries involves the use of terms and expressions which are barely intelligible to an outsider. This is to be expected and causes no particular inconvenience. Much greater problems are met daily in connection with the exact interpretation of the words of an agreement or other document in the language of an other country and in the more straightforward translation of technical terms. On several occasions in recent months we have been approached by readers overseas for advice on the choice of a technical dictionary, and we have had to admit that for aviation matters we do not know of one that has proved wholly satisfactory and up to date. The fact is that new words are added each week to the aviation language, and new shades of meaning to existing ones. Fortunately some of them become international from the outset and therefore require no translation. There is one group of words which, we think, needs some sorting out, namely, those qualifying high speed. For example, what precisely is meant by transonic? Several air craft which are unable to exceed Mach 1 or, in fact, to reach above 0.9, are freely de scribed as transonic. Yet others which achieve a fraction over supersonic speed in the dive are also described variously as sonic, transonic and supersonic. Again, the general term supersonic would by itself be inadequate in most contexts, for it permits no differentiation between, say, Mach 1.01 and Mach 10. We note that for sonic speeds regarded as high today (e.g., above Mach 3) the term hypersonic is now sometimes used, and on occasions ultrasonic. Of these two we would plead at once that "ultra" be confined entirely to those sciences which, concerned with high-frequency sound waves, have been using it for years past. If such a term is needed "hyper" is the one for aviation, if only to avoid confusion. As to what the everyday speed terms ought to mean, we would suggest that a super sonic aircraft be regarded as one that is capable of exceeding the speed of sound in level flight. A transonic machine can then be one which in level flight approaches near to sonic speed and can just exceed it in a dive. There is very little justification for extending the meaning of transonic to include aircraft which (as a whole) attain no more than the speeds at which compressibility effects begin to be felt. For the time being, however, we have to accept that some subsonic dual-control aircraft are described as transonic trainers on the grounds that they provide experience of the symptoms which a sonic machine displays on the approach to Mach 1. The high and low limits of the transonic regions have not been clearly defined. One authority has suggested 700 to 900 m.p.h., but with these figures we disagree; the high limit does not need to be higher than sonic speed of Mach 1, or 760 m.p.h. When an aircraft has reached this speed much of the airflow over it will already be supersonic. According to their shape—wing thickness and angle of sweep—some aircraft meet compressibility effects at about Mach 0.8, but their limiting Mach numbers would then probably be no more than 0.87. A sonic machine does not start to meet transonic effects until, say, Mach 0.9. Thus the transonic zone may be held to vary for different aircraft, but it is usual to think in terms of about Mach 0.8 to Mach 1. Farther Ahead After defining these sonic terms we must observe that the scientist might well regard such popular interpretations as both unsatisfactory and misleading. It is generally known, for example, that a change of airflow occurs when the speed of an aircraft increases from subsonic to supersonic; but it would be wrong to assume that a third kind of flow develops to mark a change-over to hypersonic speeds. The only new sort of "barrier" now foreseen is the heat barrier (increase in temperature with V2) and this now imposes a practical top speed limit—using present materials and altitudes —at about Mach 5. But by the time man has solved the other requirements to attain Mach 5, there is little doubt that the thermal properties of materials will have been further improved and that flight in the rare atmosphere at much greater altitudes will be quite commonplace. Aerodynamics have little place in our theme, but we must include superaerodynamics if only to introduce the term. Of this subject we claim no knowledge other than of its association with very low air densities and, for the molecules, large mean free paths.
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