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Dr. Sanford A. Moss - He Harnessed a Tornado
... and developed the modern airplane supercharger
June 1941 Popular Science

May 1968 Popular Mechanics
May 1968 Popular Mechanics - RF Cafe[Table of Contents]

Wax nostalgic over early technology. See articles from Popular Mechanics, published 1902 - 2021. All copyrights are hereby acknowledged.


Dr. Sanford A. Moss - He Harnessed a Tornado... and developed the modern airplane supercharger

Man of the Month

Dr. Sanford A. Moss, who found the secret of high flying and speed for modern civil and military planes

By Hickman Powell

Probably the happiest man in America today is Dr. Sanford A. Moss, the man who developed the supercharger, the device which makes possible the altitude, speed, and range of the modern airplane.

His greatest creation, the turbo-supercharger, at last has come into its own, after twenty years of delay, as a basis for stratosphere flying. It has become one of the most important focal points in America's sudden war effort. No effort or expense is being spared to push its mass production. At last the sky is really the limit.

Twenty-three years ago, in order to help beat the Kaiser, Dr. Moss harnessed up a red-hot tornado, sheathed it in heat-resistant metal, and hitched it up to a Liberty motor at McCook Field, Dayton, Ohio. Sheltered behind a barricade of sandbags, he opened the throttle up wide. With a wild roar of broken connecting rods the airplane engine disintegrated. The spark plugs tore out through the roof.

Dr. Moss, a small scientific gentleman with a Vandyke beard, knew perfectly well what he was doing in this seemingly irrational behavior, just as any airplane pilot today knows that you are likely to tear your engine to pieces if you open up wide at sea level with a Moss supercharger. He was giving the turbo-supercharger its first demonstration, and he did his violent deed at the insistence of a skeptical group of Air Corps engineers, to convince them that this odd contraption of his was worthy of an official test at the top of Pike's Peak, in the rarefied atmosphere it was built to conquer. At half throttle they had refused to be convinced.

On Pike's Peak, in September, 1918, the turbo-supercharger proved itself. In those days an airplane engine lost power rapidly as it gained altitude because, as atmospheric pressure fell, less oxygen was sucked in to mix with the fuel in the combustion chambers. The supercharger was a centrifugal compressor, or fan, which forced air in sea-level quantities into the engine's carburetor. In the words of Dr. Moss, it "kidded the engine into thinking it was at sea level." The compressor was revolved by a turbine driven by a whirlwind of flaming fumes from the engine's exhaust.

The test Liberty motor, which had produced 350 horsepower at Dayton, would give only 230 horsepower at the 14,000-foot altitude of Pike's Peak. But when Dr. Moss cut in his supercharger, it gave 356 horse-power. And this full power was much more valuable than at lower altitudes, for in the thin, high atmosphere an airplane could move at high speed with much less air resistance.

One of the great obstacles to flight had been conquered. Within two years engineers were bold enough to predict that eventually airplanes would attain the fabulous speed of 200 miles an hour! Within a few more years Igor Sikorsky was able to dream, quite sanely, of 100-ton flying boats crossing the Atlantic Ocean in less than 20 hours.

Strotoliner cabins are kept at sea-level air pressure by superchargers based on Dr. Moss's work

How the turbo-supercharger harnesses flaming engine exhaust gases to feed air to the carburetor at high altitudes. It is essentially a centrifugal compressor driven by a turbine. Below, Dr. Moss examining deflector plates used in the mechanism

And if this country attains its ambition to produce clouds of airplanes surpassing in performance any warplanes that Europe can build, the device which probably will do more than anything else to make it possible will be this same turbo-supercharger - patiently refined and developed, down through the years, by this same elderly little scientist-mechanic, who never has been up in a military airplane, a man so gentle that he wouldn't put a sleeping dog out of his favorite easy chair.

If, for instance, the flying fortress is the superlatively great airplane that Americans believe it to be, that is in no small degree due to the fact that its four engines are equipped with turbo-superchargers, enabling it to fly vast distances at great altitude, with an unprecedented pay load.

In these days of complex industrial engineering, it is rare that any scientific accomplishment is so exclusively associated with one man as is the supercharger with Dr. Moss. When he retired at the age of 65, on January 1, 1938, after 35 years of engineering research for the General Electric Company, every modern American airplane engine (except a few small pleasure-plane motors) was equipped with a built-in geared supercharger that was patterned after designs made by Dr. Moss.

Recognized in the industry as one of the great contributors to the advance of aviation, Dr. Moss was still a disappointed man when he retired. That was because there are two kinds of superchargers, both developed by him, but the one in common use was not his darling, his great invention, the red-hot tornado of Pike's Peak.

The commercial supercharger is a small centrifugal compressor built into an airplane engine, weighing four pounds or less, which gets its power by gears from the engine crankshaft. Its gears range to a ratio as high as 14 to 1, which means that with an engine speed of 2,000 revolutions per minute, the impeller is whirling at 28,000 r.p.m. That is no mean achievement in engineering. This supercharger is of value in improving the vaporizing of fuel and in increasing power on the take-off, as well as for its main purpose of maintaining power at altitude. Lindbergh made his flight across the Atlantic in 1927 without a supercharger, but since that time the device has had its part in every major accomplishment of aviation.

An early racing car equipped with a supercharger built by Dr. Moss. Even at sea level. the device improves vaporization of fuel and increases power

From 15,000 feet on up, the exhaust-driven turbo-supercharger takes over, allowing the engine to "breathe" normally up to 25,000, even 30,000 feet. But the trouble has been that few people wanted to fly above 20,000 feet. Satisfactory as it might be for the engine, it was both uncomfortable and dangerous for the aviator. Use of the turbo-supercharger had been limited to a few experimental ships and to a few squadrons of the most advanced Army planes. And though the Air Corps engineers worked eagerly with Dr. Moss to develop the turbo-supercharger, it never seemed to him that the tactical units made adequate use of its possibilities.

Important as it was, Dr. Moss's super-charger department never grew very large. It occupied one room in the General Electric research laboratories in West Lynn, Mass. For years the engineering staff numbered five men; then, as business increased, it was doubled. Airplane building simply was not a mass industry; and when Dr. Moss retired, superchargers were still a dramatic but tiny part of General Electric's vast business.

Now suddenly all that is changed. The little engineering staff has been multiplied astronomically. The company's best production experts have been moved in. Great factories are being rushed into commission for mass production of impellers and turbines for superchargers. Millions upon millions of dollars are being poured in.

And back on the job in the midst of it all is Dr. Moss himself, called back to work as consulting engineer - as happy, dazed, and excited as two children at the circus. At 68 years of age, his dreams have come true.

In this LePere biplane, equipped with a Moss G. E. supercharger, Lieut. J. A. Macready made a record altitude flight to 40,800 feet September 28, 1921

The story of the turbo-supercharger is the story of Dr. Moss's life, for the device is the perfect and ultimate expression of his whole scientific career. When he was 16 years old he was apprenticed as a mechanic in San Francisco, in a shop which made air compressors of the reciprocating type; and right then began a lifetime of specialization in the compression of gases and the flow of gaseous fluids. After finishing his four-year apprenticeship, young Moss boned up for entrance examinations and started as an engineering student at the University of California, sweeping up the floor of the college shops to earn his way. By 1900 he had taken his bachelor's and master's degrees, and then went on to Cornell University as an instructor and advanced student. In 1903 he received his degree as a Doctor of Philosophy.

All of Dr. Moss's research work as a graduate student had been on a project for a gas turbine, which so interested General Electric that he was taken on as a company engineer to continue the work. This turbine was to be a primary source of power, combining principles of the internal-combustion engine and the steam turbine. One part of this mechanism was a centrifugal compressor, on which patents were first taken out in 1904. As time went on this compressor became an important item of company business, manufactured for iron foundries, blast furnaces, pneumatic tubes, oil burners, and other purposes.

But the gas turbine itself had to be postponed. Regretfully it was put away on the shelf. In a scientific sense no experiment is a failure if it contributes to human knowledge, but it must have been a terrific disappointment to a practical inventor like Moss to put aside his great life project.

So matters rested at the time of the first World War. In fighting planes, altitude is one of the greatest advantages, and the idea for a supercharger occurred in various places at once. The British tried to develop a geared compressor. The French scientist Rateau had the idea of driving a super-charger with exhaust gases. The idea was all right, but the superchargers wouldn't work.

The turbo-supercharger installed at the side of the Liberty motor an an early OH-4 plane. Pilots were dubious at first about flying "with a red-hot stove"

After the United states entered the war, the National Advisory Committee for Aeronautics took up this problem, and knowing of Dr. Moss's work, turned the job over to him. It was right down his alley. His centrifugal compressor was just the thing. As for power, down off the shelf came the abandoned gas turbine. Within a few months the two had been hitched up, in the tame tornado of the Pike's Peak test.

Except for refinements that have been made through the years, that first super-charger was the turbo-supercharger of today. Its idea was simplicity itself. The compressor sent air into the intake manifold at sea-level pressure. The gases in the exhaust manifold were also at sea-level pressure, and were directed through nozzles on the buckets of the revolving turbine.

Technical discussions of the turbo-supercharger are discouraged in these days of military secrecy; but the difficulties are easily apparent to anybody who has ever had trouble with an overheated bearing. The exhaust fumes are at 1,500 degrees F. Manifolds and buckets are red hot, while the turbine revolves at 20,000 or more revolutions a minute. And on the same drive shaft, only a few inches away, the compressor is handling atmosphere which has been recorded as low as 76 degrees below zero! The turbine emits a four-foot tongue of flame, which at high altitudes freezes instantaneously, and on occasion has settled as ice on the wings of the airplane itself.

A turbine bucket is a little fin like a blade on a windmill. In the Moss turbine the buckets are a fringe of little blades, of a secret heat-resistant steel, mortised into the rim of the turbine wheel. Tested at 22,000 revolutions a minute, a turbine bucket is traveling 1,000 feet per second, in a circle less than 12 inches in diameter. Weighing less than 1/100 of a pound, a little red-hot bucket at this speed is subjected to a centrifugal pull of about 1,750 pounds.

Moss's first turbo-supercharger was light enough for one man to carry. It was figured that a commercial compressor delivering the same amount of air would weigh 5,000 pounds and occupy a space of more than eight cubic yards.

Experimental work with the supercharger was interrupted by the Armistice of 1918. The time was yet to come when it would be tested in an airplane. Pilots looked at it dubiously. One of them described it as a combination cook stove, blacksmith forge, and flying junk shop. An airplane engine itself is a sufficiently terrifying bit of leashed power. A red-hot turbine, revolving at 20,000 r.p.m., was hardly a comfortable companion in the crates which aviators flew in those days.

On September 27, 1920, Major R. W. Schroeder took off in a biplane fitted with Dr. Moss's turbo-supercharger. At 25,000 feet he encountered a head wind so strong that he drifted backward. But he went on, up and up, until his instruments recorded 33,000 feet. At this altitude his goggles frosted over. As he struggled with them his oxygen supply gave out. Unconscious, he dived for nearly six miles.

Schroeder never did understand how he got that plane back on the ground. Half recovering his consciousness at a few thousand feet altitude, he managed to right the plane. He could hardly open his eyes. But somehow he managed to land safely.

As Dr. Moss improved the supercharger, altitude records were broken again and again, establishing the pioneering fame of the Army aviators Macready, Stevens, Street. But the difficulties encountered by Schroeder have never been really conquered. Only recently the Mayo Clinic, after researches on the subject, announced that a man deprived of oxygen at 35,000 feet would die almost instantly. Even with an oxygen mask, at that altitude and low pressure, a man does not function normally. Army flyers in pursuit ships are under orders to use their oxygen tubes when above 10,000 feet.

In the years just preceding the present war, there were encouraging experiments with planes built with sealed cabins, within which warm air was kept at pressure. But such cabins are not punctureproof and will be less useful in war than in peace. Provision of adequate oxygen for high flyers is one of the major problems of the present war.

Miraculous as the advance of aviation has been, the slow development of stratosphere flying has of course been discouraging to Dr. Moss. That it has developed at all has been due largely to an irrepressible, impish quality of the inventor, who for 20 years encountered what he called the "glassy eye" of industrial executives and Army brass-hats, and would not accept discouragement.

At the time of his retirement an anonymous writer in "Mechanical Engineering," who must have known him very well, described him thus:

"Painstaking, nervous, his eyes sparkling with fun or fury, Dr. Moss raises his pointed beard in his companion's face and looks at him through the lower lenses of his glasses. His tongue, trying to keep up with an agile mind, is ready for a persistent barrage of embarrassing questions or a volley of explanations. He possesses that disarming characteristic of small boys with whom it is impossible to be angry for long in spite of sometimes exasperating behavior. Once you have met him you never forget him, but think of him in terms of warm affection."

Back in the days when General Billy Mitchell was unsuccessfully fighting the inertia of Army commanders, Dr. Moss was carrying on his own private war against the same thing. They couldn't get rid of him, yet they couldn't get mad.

He is a man of many engaging idiosyncrasies, and his friends have an apparently inexhaustible supply of anecdotes about him. He always carries a pocketful of quarters, and engages everyone possible in a coin-matching contest, explaining that this is not gambling because the laws of probability will certainly bring him out even at the end of the year. While enjoying a short vacation at a summer camp with some of his associates from General Electric, he was voted the "best sport." That was after he had been assigned, as his share of camp work, to be valet to a team of mules. He turned up for work, equipped with an ash can, a freshly laundered white-wing suit, and a high silk hat.

He has a habit of asking young men what their pleasures were as children, and out of such researches has evolved an aptitude test which General Electric uses in its personnel work. His theory is that education should be concentrated only along the lines of the pupil's aptitudes. "A young fellow who never took a clock apart can never become a mechanical engineer," he says. He doesn't care whether the clock was ever put together again. What counts is the curiosity - the desire to know how things work.

Once Dr. Moss argued unsuccessfully before a police-court judge, with elaborate mathematical formulas, that a speed cop could not possibly have clocked him accurately, because the cop had to go faster than he, to overtake him. More successfully he once defied a traffic cop who told him to pull over to the side of the road. "I won't do it!" he exclaimed. "The law says I can't drive without my license, and you've got it!"

On occasion, to get some place in a hurry, Dr. Moss reluctantly has flown in a commercial airplane; but he has never been on an experimental flight. "It would contribute nothing to the development of the turbo-supercharger, so I just don't do it," he explains. Once his associates at Wright Field ganged up on him, insisted that he must go up with them for consultation. He put it off to next day, and in the morning a telegram arrived from General Electric, expressly forbidding Dr. Moss to make the flight. Triumphantly he obeyed.

This reluctance seems to have nothing to do with courage. No one but a brave man would fool around with experimental turbines. During the test of the supercharger at Pike's Peak, his associates had to tie him to a post with a piece of rope, while he worked on the engine, to keep him from absent-mindedly backing into the whirling propeller.

In all his triumph, Dr. Moss is still able to find good-natured cause for complaint.

"First they told me it couldn't be done," he says. "Then they said, 'What's the good of it?' And now what do they say? They say, 'We were going to do it all the time.'''

Now that the turbo-supercharger is really being developed, Dr. Moss is bursting with ideas of how it could be used for peacetime purposes. But he still encounters the "glassy eye." Nobody will listen. All they think about is providing the stuff to win a war.

Back in the old days he could complain, argue, make propaganda, fight for his ideas. But this time he is stumped. The turbo-supercharger is now so important that they won't let him say a word about its present or its future.

Even his dreams are military secrets.


Uncle Sam's flying fortresses owe their ability to fly high, fast, and far, to the fact that their engines have turbo-superchargers




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