National Geographic : 1926 Dec
EXPLORING THE EARTH'S STRATOSPHERE Such ceilings as I have cited, however, are extremely low compared to those dealt with in high-altitude flights, where the question of rare air adds its complications to the problem; for, as the altitude be comes greater, the air becomes less dense and its power of pressure within the engine falls off. This statement becomes clearer if we realize that the air pressure, which at sea level, where we normally breathe, is 14.7 pounds per square inch, at 35,000 feet has diminished to 2.5 pounds per square inch, and that a Liberty engine which at sea level develops 400 horsepower, at 25,000 feet, because of this thinner air charge, can, with all its efforts, muster forth but 87 horsepower; and at 35,000 feet, of course, even less. Obviously, the engine cannot force a heavy airplane higher on a starvation diet, and it was realized early in the altitude game that, to enable it to do so, some mechanical aid would have to be devised to keep it supplied with air of sea-level pressure-air that would feed to it its necessary quota of oxygen even when it traveled above the normal oxygen zone. THE SUPERCHARGER MAKES HIGH ALTI TUDES POSSIBLE To fulfill this need a device was in vented which compresses the rare air of the high altitudes to sea-level density and forces this compressed air into the carbu retor, which in turn sends the proper com bustive mixture to the engine cylinders. This instrument, called a supercharger, will increase the ceiling of any plane upon which it is installed thousands of feet; more than that, with sea-level power in its engine, the climbing ability of an air plane is greatly increased, as this rare air offers much less resistance to the airplane surfaces than does the denser air of the lower altitudes. The supercharger which I have used on my extreme altitude flights is a turbine wheel, which is revolved at great speed by the exhaust gases of the engine. Tests have shown that this turbine wheel, ap proximately one foot in diameter, makes about 40,000 revolutions per minute at 38,000 feet. It is difficult to conceive of such speed, equivalent, as it is, to 666 revolutions per second. It is rather incongruous to think of gen erating heat from this thin, frigid air, sometimes colder than eighty degrees be low zero, Fahrenheit. When compressed by the turbine supercharger, however, its temperature rises almost instantaneously, so that a radiator or inter-cooler had to be designed as part of the supercharger mechanism to cool the air before it reached the carburetor and cylinders. PILOT'S DIVE THROUGH CLOUDS EXTIN GUISHES FIRE Before the perfection of the intercooler, this hot air caused preignition and mal functioning of the engine, cutting short many a test flight. During the early ex periments with superchargers, in fact, something was always sure to break in flight. Pipes and bearings have failed and parts of the supercharger have flown off in mid-air, making it necessary for the plane to descend in trouble. One test I shall never forget. I had gone up against my better judgment, as the sky was completely overcast with clouds at 20,000 feet; but the test was an important one, the engineers being ex tremely anxious to acquire certain data before letting a large contract. Roy Langham acted as my observer on the flight, and we obtained most of our information before reaching the clouds; then thrust up through them, as what we had acquired would be of no value unless the test were completed. Above the clouds we flew a level or speed course at full throttle. Toward the completion of this course fire broke out in the engine, ignited the lubricating oil, and a dense cloud of smoke poured forth. I immediately plunged downward through the clouds, the dive putting out the fire, although the engine mount was still smok ing. I was lost. I could not see Dayton below or any recognizable landmark. Be fore we went up, Langham had been in structed to keep tab on our location, as I would be busy with the instruments. Now I turned about as well as I could in my bulky clothes and oxygen mask and tried to let him know, by pointing de cisively toward the ground, that I had lost my bearings; then I turned to straighten up the ship.