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Aviation History
1942
1942 - 1230.PDF
582 FLIGHT JUNE IITH, 1942 STRATOSPHERE FLIGHT 1 m some 45,000ft. remains essentially unchanged, and is 21 per cent, oxygen, 78 per cent, nitrogen, some 0.03 per cent, carbon-dioxide, and about 1 per cent, of inert gases of which the chief is argon. For the smooth working of the human machine an ade quate and normally rated oxygen supply is absolutely essential. Since the density of the air decreases with the altitude, the amount of oxygen which the body draws by breathing is considerably reduced. The resulting oxygen- want causes a complex of physiological and psychological symptoms. To start with, the affected person does not experience any harmful sensation and is only in a queer state comparable with alcoholism. Characteristic of this state is the complete absence of the critical sense, incapacity to perform simple and accustomed manual and mental functions, lack of co-ordination and control of the body ; indeed, a real disintegration of the personality. Another most important and significant effect of the reduced oxygen content of the air on the pilot is the reduced dark-adaptation. Since this is essential for the efficiency of a night-fighter pilot, it has been suggested that oxygen should be supplied to crews at a lower altitude at night. Ultimately, the deleterious effect of oxygen deficiency may bring the human machine to a complete standstill. The Importance of Oxygen Investigations carried out in laboratories reproducing conditions prevailing in higher altitudes have shown that up to 10,oooft. a normal individual is not affected by the reduction in oxygen supply. After this height there is a zone of adjustment where the body can compensate for oxygen deficiency by intensified respiration. After about 13,000 to 16,400ft. lies the lower limit of the zone of incom plete compensation, bound above by the critical line which leads into the zone of death due to altitude effect. Because the reserve of oxygen in the human body amounts only to 400 c.c, or enough to maintain life for 1 \ minutes, the permanent supply of oxygen "is vitally important if the negative effects of the higher altitudes are to be prevented. This is achieved by addition of oxygen to the inspired air by means of a special breathing appliance, the oxygen mask. With modern fast-climbing aircraft the oxygen mask becomes a most necessary part of the equipment, not only for specific altitude perform ance, but for those eventualities in which the pilot may have to seek higher altitudes. Oxygen masks are used as low as 15,000ft., and are an adequate source of oxygen supply up to an altitude of 30,000ft. Above this height the atmospheric pressure is so much below that at ground level that the oxygen saturation of the blood system is so low that even the breathing-in of pure oxygen is not sufficient. In flights above 30,000ft. pressure suits or pressure cabins are, therefore, being used to compensate for the reduction in the outside atmospheric pressure. Originally, pressure suits were mainly used for various high-altitude record flights, but, since the higher regions are gradually becoming the normal zone of flying, pressure cabins are increasingly coming into service. They enable flights of longer duration to be made in high altitude in comfort. Effect on Equipment The effect of conditions prevailing at high altitudes is not limited to the power plant and the human body. The controls of the aircraft have to work under conditions entirely different from those for which they were originally designed and made. Very low temperatures cause control mechanism to bind at some places and loosen up at others because of the difference in contraction of different metals. Fabric-covered rubber hose becomes so rigid and fragile that it frequently breaks under vibration and splits wide open. Lubricating oils tend to solidify at verylow'tem peratures, and cause the stiffening up of controls, thus con- The two main layers of atmosphere with their temperature characteristics are here shown diagrammatically. siderably reducing the manoeuvrability of the aircraft. The problem of special lubricants is also apparent in all hydraulically operated parts of the aircraft. Special lubri cants which solidify below the lowest occurring tempera tures are necessary. The efficiency of some instruments may be impaired both by the low temperature, which causes some pSistic material used for their castings to become very brittle, and by the different atmospheric pressure. Finally, the efficiency of the airscrew in the rarified atmosphere presents a special problem if the increased per formance of the aircraft is not to be lost. In specially equipped ground laboratories these negative effects of high altitudes on the human body and aircraft equipment are being carefully studied. And it is thess constant researches and experiments which have largely .succeeded in eliminating the difficulties and in creating a variety of new equipment made to withstand the peculiar conditions of high-altitude flight. Protection for "George" " /^EORGE " is, as most readers of Flight will know, tfe vJ nickname given to the automatic pilot which on loiig flights relieves the pilot of the need to control the aircraft, so that he can devote his time to other duties, or take a brief rest if circumstances permit. The apparatus was, as our readers may remember, the invention of two technicians, Mr. F.' W. Meredith and Mr. P. A. Cooke, while they were employed at the Royal Aircraft Establishment. The manu facturing rights were secured by Smith's Instruments many years ago, and both inventors have left the R.A.E., Mr. Meredith to join Smith's and Mr. Cooke to take charge of instrument and much other equipment at M.A.P. The normal life of a patent is 16 years, and an invention must be of very great merit to secure a prolongation of the patents, even for a period of five years. Recently a petition was made to the Courts, asking that the patent rights of the automatic pilot (there are four in all) might be extended beyond their normal term. The petition came up for hearing on May 18th and 19th, and, after evidence had been given on behalf of the petitioners, the Court decided that the in vention was of sufficient merit to warrant the granting of prolongation, not only for the five years usual in such cases, but for a period of eight years. . It might be pointed out that in the history of patents th<?re are very few cases in which prolongation of patents has been granted for more than five years, so that it will be realised that quite exceptional merit was attached to the Smith's Auto matic Pilot.
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