Evening Republican, Volume 21, Number 254, Rensselaer, Jasper County, 10 November 1917 — UNIQUE TEST FOR LIBERTY ENGINE [ARTICLE]

UNIQUE TEST FOR LIBERTY ENGINE

American Aviators Won’t Have to Experiment While Flying Over Enemy. TWO PROBLEMS TO SOLVE jA United States Bureau of Standards Has Devised a Way to Reproduce the Conditions Found In High Altitudes.

Washington.— : The bureau of standards is erecting a littlp greerilsh-gray concrete building on the edge of its grounds where one. of the final chapters of America’s preparations for aerial warfare will be written. The declines to discuss what part it will play In the final design of the new “Liberty air engine” which the government Is expected to mount on all American airplanes for use In the European war, but It has become known that before the final design of this engine Is approved it must undergo a few final tests in that little green-ish-gray building. There will be determined, under conditions almost Identical with conditions found at various altitudes, Just how an airplane engine performs . when it gets so high that the air gets perceptibly thinner. 'lt will be tested in a temperature down to freezing. Bringing High Altitude Down. The bureau building is a tomblike structure, full of delicate instruments which will have the effect of bringing the skies down to the earth, insofar as airplane conditions are concerned. It Is impractical to £end an engineer aloft to watch thf?> engine perform up there, so the bureau plans to bring the skies to the engine. Ever since the European war began, the aviators of the warring nations have been flying to astonishing heights in the clear air of France. Altitudes of 10,000 feet are quite commonplace, and 20,000-foot flights nolonger excite wonder. Aviators must go up high, and they must have engines that will take them there, so the engine

designers have been experimenting for the last three years with an engine that won’t "smother” when It gets Into —tain air. So far the allies have been unable, for various reasons, to make absolutely accurate tests. An engineer can go aloft in a plane, but he can’t load In a ton or two of apparatus also and test out “sparking efficiency, compression density, horsepower delivery and all the other things that he should do. Being confronted with the necessity of making such tests, the bureau of standards experts figured out a method. The Two Problems. First, they argued, they must know just what an airplane does at an altitude, say of 20,000 feet. An engine that will perform perfectly at 10,000 feet has a tricky habit of “stumbling” and missing ignition when It gets another 10,000 feet higher, and the experts wanted to observe all Its ailments at that height. Second, they wanted some sort of a mechanical arrangement which would permit them to test untried types of engines under conditions Slmllar to conditions very high aloft, and

to approye or condemn the performance of these untried types. So they set to work to build a concrete, tomb-like structure, about IS feet long by 6 febt wide and 6% feet high. This concrete chamber was so constructed that it could be made a vacuum if necessary. The walls are 12 inches thick and tarred on the outside. They needed because at 20,000 feet altitude the air pressure is about seven pounds to the square inch —about half the pressure at sea level. That me.ant that when the scientists got to duplicating air pressure at 20,000 feet the walls had to support an outside pressure of air equal to eight pounds to the square inch. If the walls were not built thick they w'ould crush in like paper. Either Hot or Cold. Then a complete heating and refrigerating plant was installed so that when the four or six big fans which are to whirl the air over the engine at 40 miles an hour start their gale it will be down to the temperature that one finds thousands of feet up. Into this air chamber they expect to put the engine type that is to be tested, mounted so that it can tilt forward, backward or sidewise, just as it would behave in the air. As soon as everything is ready the doors are locked and made airtight, and the engine is started. When it starts, the air on the inside of the chamber is the same density as the outside air, but when the engine -begins to suck in air to make explosions the Inside atmosphere rapidly becomes exhausted. The chamber is provided with an intake valve which will admit the air that is needed. The chamber is also provided with glass windows, through which the experts may watch instruments which register the air pressure and the temperature of the chamber. By data securedJn_actual flights the bureau experts know the exact density of the air at each of the various hundred foot levels. An ordinary aneroid barometer would give this data only approximately; , When the engine starts

and begins consuming air on the inside of the chamber the inside pressure begins to drop from“Ts pounds to the square inch to 14 pounds, to 13 pounds, and so_on, until it has reached a rarity that corresponds to a great height.——— As soon as it reaches this rarity the intake valve is opened slightly, and only enough air Is admitted to take the place of the inside air that the engine is consuming. This, of course, keeps the pressure Inside at the desired rarity, and to all intents and purposes the engine is now flying at an altitude of 20,000 feet. General Mobilization. As soon as the engine starts, other parts of the chamber’s machinery start too. For instance, the exhaust begins to work. It would be utterly impracticable to discharge the gases from the engine into the outside air through the ordinary exhaust pipe. With the air inside at seven pounds pressure and the outside air at 17 pounds the force of the outside pressure would jam a great quantity of atmosphere back up the exhaust pipe, fill the chamber with fumes and smoke and reduce the inside pressure to normal. To overcome this the experts designed a blower attachment w’hich will suck the gases and fumes from the en-

gine with a force sufficient to prevent the outside air from rushing in. Also, the fumes and gases will pass through pipes which spray these gases with cold water, thus keeping down the temperature in the chamber. The actual horsepower performance of the engine can be determined without trouble. Every ounce of pull it generates is transmitted to"i big electric generator on the outside, and the amount of electricity generated by the engine’s power makes it perfectly simple for the scientists to determine when the engine is faltering. Through the glass doors of this concrete chamber, the scientists will observe the engine Itself or the instruments attached, which will register every performance of that piece of, mechanism. If it won’t work in an air-pressure of seven pounds to the inch, that engine will never do for high observation work. \ • Testa Pre-Compress’on Also. Broadly speaking, this is the chief use to which that concrete chamber still be put. It has another use, however. That is the testing of pre-com-pression devices. It has been found advisable to equip all airplanes that are expected to attain gfeat height—with a pre-compression attachment. This is designed to gather and concentrate a quantity of air and at the moment of each discharge of the cylinders, Inject it into the cylinders to supplement the deficient supply that the engine can take through its Intake valves. ’ There are many of these pre-com-pression devices being offered to the government, which at this time cannot be proven except under actual battle but with the use of the rarifted air chamber at the bureau, the government experts can decide within value of the device.