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Aviation History
1947
1947 - 1781.PDF
OCTOBER I6TH, 1947 F LI G HI 435 l'rc* vii ri»u lion Some Problems of Cabin Air Control, and Modern Trends in Their Solution By W. M. WIDGERY, F.R.Ae.S. THE first lecture of the autumn session of the RoyalAeronautical Society was delivered by Mr. W. M.Widgery, F.R.Ae.S., last Thursday. It was pre- ceded by a short ceremony at which Sir Frederick Handley Page handed over the presidency of the Society to the new president, Dr. H. Roxbee Cox. Before he relinquished office, Sir Frederick presented the Society's awards of medals to the recipients. They were as follows : The Simms Gold Medal to Professor Leslie Aitchison for his paper "Aeronautics and Metallurgy"; the George Taylor (of Australia) Gold Medal to Professor A. R. Collar for his paper "Aeroelastic Problems" ; the Wakefield Gold Medal to Mr. Edward Link, inventor of the Link Trainer, for apparatus tending towards safety in flying (in the absence of Mr. Link, the medal was presented to the American Civil Air Attache, Mr. Satterthwaite) ; the R.Ae.S. Silver Medal to Mr. W. G. Carter for his work on jet-propelled aircraft; the R.38 Memorial Prize to Mr. J. K. Hardy for his paper "Protection Against Ice Formation" ; and the Edward Busk Memorial Prize to Mr. J. Smith for his paper "The Evolution of the Spitfire." Mr. Widgery introduced his lecture as an account of therecent developments in aircraft construction which were com- monly embraced by the term " pressurisation." In his opinionthis bald name gave a crude and misleading picture of the developments which were now in hand, and both he and theorganization to which he belonged preferred, he said, to speak of "cabin air control" as that name did, in fact, give a clearpicture of the scope of the paper. The evolution of pr^senger-carrying aircraft had at the Mr. W. M. Widgery, F.RAe.S., of Westland Aircraft Limited, has been engaged from 1944 until the present time in research and development of pressurised cabins for civil aircraft. He has been concerned with the design and development of much spzcialized equipment for use on the new types of aircraft now under construction. The experimental decompression chamber &. Normaiair Ltd. in which fuselage specimens up to 15ft x Vift be tested. outbreak of war reached a s|age where a great deal of attentionwas paid to the comfort of passengers, and it was fair to describe pressurisation as a development directed almostentirely towards the greater comfort of the occupants of aircraft. He considered that up to the present, and probablyfor some time to come, the problems of pressurisation, safety and comfort would be inextricably bound up.The lecturer drew attention to the serious handicap to civil aviation of the oxygen system, since the majority of passengershad psychological objections to the wearing of masks. In any case there was a limit to the height at which oxygen couldbe used effectively, and he quoted 43,000ft as the height at which the individual was unable to do without pressurisation.Fortunately the composition of the atmosphere varied but slightly with increasing altitude, so that ground level, orany other chosen low-altitude atmospheric condition, could be restored by increasing the. pressure within the cabin. Theone exception was that moisture content fell ofl rapidly at greater heights. Up to the present time civil aircraft hadnot been operated above 25,000ft, at which height oxygen alone would, from the physiological point of view, be a satis-factory alternative to pressurization, so it might be fairly assumed that pressurisation had been developed purely to givegreater comfort. Choice of Pressure Referring to the choice of pressure in the cabin, Mr. Widgerysaid that a number of important considerations influenced the decision, which, in general, were similar for civil and militaryaircraft. There was, however, one fundamental difference, and that was that on military aircraft complete failure of thepressure system might occur at any time due to enemy action. Practical experience during the war had shown, however,that the ill effects of a sudden loss of pressure were minimized by confining the pressure to that minimum vital to maintainrighting efficiency of the crew, and, consequently, they were compelled to wear oxygen masks when flying at the greateraltitudes. There was, he said, another risk in the form of explosive decompression, the physiology of which was outsidethe scope of the paper, but he mentioned that the seriousness of the consequences was a function of time and expansionratio, since the time for decompression was closely related to the volume of the cabin It should be noted that aircraftwith small cabins, for example, fighters, should be down at the minimum permissible pressure in combat, but in cabinsof large volume serious physiological consequences were unlikely to result from sudden release of pressure due to thetype of failure which might be expected, such as the blowing- out of an observation panel. The ideal pressure for civilaircraft was, he considered, ground-level pressure since pressure within the cabin would remain unchanged and thepilot would be free to climb or descend at any rate which was desirable for other reasons There was agreement, however,that unselected passengers could be subjected without undue risk to a reduction of pressure equivalent to that experiencedat 8,000ft, and that pressure was set on aircraft now going into service With present systems, with an operational ceilingof 25,000ft, the necessary pressure was 5J lb/sq in for 8,000ft, compared with 9.4 Ib/sq in to maintain ground level con-ditions. Fresh Air Supply.—The amount of fresh air per person perminute in normal cruising conditions with duplication of blowers was considered to be 1 lb, with a minimum of 0.6 lbwith one blower out of action. Single blowers had been fitted to British fighters which delivered 5 lb of air per minuteat 40,000ft. The criterion was the minimum flow necessary to neutralize small leaks rather than the needs of the pilot.Of the rate of change of pressure, the lecturer said that data had shown that passengers, when awake, were not incon-venienced by rates of change up to the equivalent of 300ft per minute, but when asleep they might suffer serious discom-fort if the rate exceeded 150ft per minute. Speaking of temperature he said that in the cabin it should
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