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Aviation History
1941
1941 - 1274.PDF
JUNE 5™, 1941. HIGH-ALTITUDE FLIGHT (Above) The Bristol 138 taking off on its record-breakingflight of June 30th, 1937, when it reached 53,937ft. Note the large air intake. (Right) Extremes meet. Fit. Lt.Adam's high-altitude pressure suit resembles that of a deep-sea diver. (Below) A closer view of the helmetedpilot just before the take-off. In air transport the pressure cabin has been developed for use at altitudes much lower than 30,000ft. because the passenger cannot be reckoned to be as fit physically as the air force pilot, and in fact should not be taken above 14,000ft. without either oxygen or a pressure cabin. (Long periods even at 12,000ft, can sometimes cause ill effects.) So in achieving high-altitude flight, the first of the three major problems to be surmounted is the human body. The other two are the aero engine and the pressure cabin or pressure suit (which may be regarded as a miniature pressure cabin which the wearer takes with him). The Atmosphere and the Body Both the pressure and the density of the air decrease as we go up, and the graph shows how the density has fallen to one-quarter of its sea level value at 40,000ft. It is at 34,000ft, that the pressure has fallen to the' same fraction, and it is pressure with which the body is vitally concerned. The proportion of oxygen in the atmosphere is constant and does not lessen as we go up, as is sometimes thought. What does lessen is the pressure available to force the oxygen into the blood stream from the air in the lungs. The pressure of the atmosphere is the sum of the pressures of the gases composing it, and these are nitrogen, car- The late John Tranum, well-known parachute jumper, in a Siebe Gorman test chamber. bon dioxide and water vapour, as well as the oxygen. As altitude increases, the pressure of each of the con- stituent gases, as well as the air pressure, decreases, and so the body gets less oxygen. But by increasing the pro- portion of oxygen in the breath by using an oxygen mask, the pressure of the oxygen constituent of the air is in- crea^sd and the body receives more nearly the amount to which it is accustomed. But there is obviously a limit to this process, for there comes an altitude at which the air pressure is so low that not even if pure oxygen is breathed is the body able to absorb enough into the blood stream. This altitude is. about 40,000ft., the pressure here being just under one- fifth of that at ground level. At this level a pressure cabin or suit is essential, but it is desirable at altitudes- considerably lower. AnoxaBmia The reason for this is a complaint known as anoxsmTiiu^ which is simply "oxygen want." When a pilot does not get enough oxygen he cannot think or act normally, but suffers very much from both physical and mental- tired- ness. His judgment and memory are poor, and he cannot think quickly or accurately. " What's that little dial say? . . . Six, is it? Six what? . . . Six o'clock, I s'pose. . . . No, can't be that. . . Oh, yes, boost, that's it, of course, boost pressure. . . . Boost is six, six is boost. . . . Why shouldn't it be? Six boosters, six roosters. Oh, who cares about roosters anyway? " Forgotten is the fact that the dial is there to warn him that he may be using a boost pressure damaging to his engine—and forgotten are many other things, too. Without an adequate supply of oxygen the pilot becomes a victim of '' pilot error,'' and may do quite unaccount- able things, forgetting the simplest facts and making the silliest mistakes. Too little oxygen and too much alcohol have effects- very closely related, in that the more one is affected the 1 better one feels! But oxygen want is dangerous, and i^ the brain is completely cut off from its oxygen supply it will die in seven or eight minutes. So will animals j exposed to the low pressure of 50,000ft., even if supplied \ with an atmosphere of pure oxygen. Another effect of high altitude is loss of weight due to the lowering of boiling point, so facilitating the evaporation
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