When the war is ended, commercial aviation will certainly take over where it left off on the subject of high altitude flight. But the lessons learned in high altitude warfare will have been invaluable, for some of the greatest research in aviation has been with the wartime use of oxygen.
Almost any schoolboy knows the wartime value of high flight flying out of ack-ack range, getting between the enemy and the sun, the ability to dive upon the prey, and the ability to evade interceptors slowed up by necessary climbing. In peacetime, the rarified high altitude air becomes valuable for faster flight because of less air resistance, while such flight avoids air disturbances and most bad weather conditions. Adjusting the airplane to the sub-stratosphere is not too difficult but introducing the average passenger to these conditions is a ticklish job.
The changes inflicted upon the compensatory mechanisms of the body by high altitude are primarily changes in temperature and changes in pressure. The proportional content of oxygen in the upper atmosphere is quite constant, but the whole amount of air becomes thinner, and therefore the weight (and pressure) of air is less as we proceed upward.
An adequate and uninterrupted supply of oxygen, at sufficient pressure, is necessary to the support of life. Pressure is needed to force oxygen to our bloodstream, and at high altitudes although we breathe good air, our bodies starve for oxygen because there is no pressure to push air to the tiny alveoli (lung tissue) and supply the oxygen-thirsty bloodstream. We remedy this by breathing oxygen through a mask, thus making the job of oxygen-separation easier for the body, which would otherwise suffer because of low pressure air. At twenty thousand feet, a height that does not seem very high in this Air Age, the atmosphere's pressure is less than half that at sea-level!
Oxygen equipment at first, reminds the average passenger of "gas" taken at the dentist's. Some even have a dread of the "smothering effect" of a mask, but pilots who use the oxygen-mask feel at home with it, even at lower levels. Although one may profess to "smell" oxygen, it is only the rubber equipment that smells for oxygen is odorless. There is definitely no smothering effect, as the mask mechanism works almost as a part of the anatomy and without any human effort. The oxygen used in the mask is no substitute gas but the very same we breathe at all times, and the person who has used the mask (every air-minded person should be initiated) loses distaste for the idea at once. Pilots report that flying from coast to coast at high altitudes using oxygen is often less tiring than making a short hop without oxygen.
At sea level, the blood is normally saturated with oxygen to the extent of 95 percent; as we proceed upward and the saturation decreases, our brain (the first organ to be noticeably affected) loses its aptness and plays queer pranks. The effect is often similar to alcoholism you may have a "crying jag" or you may have a feeling of great joy, laughing aloud, exclaiming how good you feel. Instruments may be seen, but you will not know whether they measure oil, pressure, temperature or bananas. And the amazing thing is that you don' t care. You will always feel confident that you can go higher that you do not need oxygen, while actually your sight is dimming, your senses failing and your coordination as a pilot is not worth a darn! Such is the insidious effect of anoxia or lack of oxygen.
In wartime, when one member of a crew is overcome by aeroembolism, the mission of the whole crew may fail, This is the pain caused by nitrogen bubbles at altitudes usually in excess of thirty thousand feet. Some persons are more easily affected than others; the low-pressure chamber test is valuable for determining these individual reactions. Aeroembolism is the flyer's version of the deep sea diver's "bends." The only remedy is an immediate descent to higher pressure atmosphere.
The fact that body gases expand in ascent may become very painful and embarrassing to the extent of making high altitude commercial flights a real problem, Body gases, especially those created by having eaten cabbage, beans, soda-pop, hot-dogs and many other American lunch-time favorites, expand and seek outlet. If the intestines are already distended at sea-level, they will become over twice as distended at 20,000 feet, At very high altitudes the low pressure outside air permits inner gases to expand five and six times their normal space, forbid the thought! Again, the altitude ceiling of the passenger sub-stratoliner (except for pressure-cabin compartments) might well be the ceiling of the weakest passenger. Pressure cabin research has been carried on in warfare, especially to reduce danger to wounded patients who could not stand internal gas-expansion. Such "hospital" ships will probably be the sub-stratoliners of tomorrow.
Last and easiest gremlin for the human body to lick, is temperature. Of course, the stratosphere temperature hovers at about -67° F, but the modern airplane is capable of being well heated. Rather the airplane itself suffers from low temperatures, for metal shrinks, rubber becomes brittle and oil becomes like tar in stratosphere coldness. The human body has great compensatory equipment which sometimes outdoes the machine, but nothing tests it as unmercifully as being lifted suddenly from a warm high pressure world into a freezing low pressure hell.
Frozen fingers and frost-bitten faces of waist gunners who must fire through open side panels to hit the enemy at high altitudes daily attest to the rigors of combat operations in the upper reaches of the air. Only the devastated German cities suffer more from our conquest of the stratosphere.
This article was originally published in the August, 1943, issue of Air News magazine, vol 5, no 2, pp 32-33.
The original was printed on 10½ by 13½ inch paper. Pages have been reduced to print on letter-size paper.
A PDF of this article is available. It includes a chart showing the effects of altitude and 4 photos: Boeing B-307 Stratoliner, Republic P-47 Thunderbolt, Lockheed Lodestar and Brewster F2A-1 Buffalo.
Photos are not credited.