As the inventor of the alternating current, the world is indebted to Mr. Tesla for the use of electricity carried long distances. He now discusses the probability that airplanes will rise to great heights and travel at speeds that seem incredible. This article is written, in part by Mr. Tesla himself. The rest is written from stenographic notes. It gives, very likely, a glimpse of the immediate future.
Sitting in his office on the twenty-fifth floor of the Woolworth Tower, Mr. J. Pierpont Jones, American business man, will one day glance at his watch and discover it is 3 o’clock in the afternoon.
“By George,” he will say, buzzing for his secretary, “If I don’t hurry I’ll be late for that dinner engagement at the Savoy!” And as his secretary answers the buzzer:
“Charles, when does the next London bus leave?”
“Three-thirty, sir,” says Charles. “You can make it if you hurry. The car is waiting.”
And fifteen minutes later Mr. J. Pierpont Jones will emerge from the elevator on the aeronautic landing stage of lower Manhattan, climb into the hermetically sealed steel fuselage of the New York-London Limited, which will rise promptly at 3:30 p. m. At seven that night he will climb out of his compartment on the landing stage on the Thames Embankment, and descend to meet his friend for dinner.
The three-hour aeroplane trip from New York to London, flying above the storm level at eight miles above the earth’s surface is the possibility of the immediate future.
This is not my own prediction. It is the result of sixteen pages of close calculations in higher mathematics made by Nikola Tesla, to test and check up other pages of intricate calculations made by Samuel D. Mott, charter member of the Aero Club of America.
Mr. Mott asserts that the three-hour trip to London from New York is a question of rising into rarefied air where the air pressure is only one-fifth what it is at the earth’s surface, at which point the “altiplane”, as he has named the flying machine of the future, may be expected to fly five times as fast as at the earth’s surface. And if the speed of the aeroplane is increased not five times but only one-fifth, Mr. Mott says the trip will be made anyhow in the rarefied air eight miles above the earth’s surface in not more than
twelve hours running time.
And Nikola Tesla agrees that taking a plane to such an altitude must result in great increase in speed, although he does not wish, in the absence of exact knowledge of certain factors entering into the problem, to predict exact speeds.
Speaking before the Pan-American Aeronautic Convention at Atlantic City, Mr. Mott asserted that in order to avoid being weather-bound as were the aviators at Newfoundland, it will be necessary to construct planes that will rise above the storm limit.
“I submit,” he said, “that waiting indefinitely for ideal weather conditions for long-distance flying over land or sea will not do for the demands of commerce. Therefore I would bring to your attention the possibilities from the airplane or hydroplane, to go into the stillness of nature above the weather.”
WHAT THE PROBLEM IS
“The problem is evidently one of equipment of our planes to function in rarefied air, and protection of navigators against its tenuity; likewise protection of their body warmth and comfort in extremes of temperature. How high we may go no one may know until tested. Personally I believe it possible to go fifteen or twenty miles aloft, if necessary. It is obviously a matter of equipment plus climbing ability of aircraft designed for the purpose.
“What is the object of high flying? Daily experience shows us that high speed and density are incompatible. We know that we must furnish aircraft with four times the power to go twice as fast, and the marine engineer knows that he must furnish eight times the power to go twice as fast. In other words, from the ultimate height of the air to the earth’s core pressure is progressive. Thirty-three feet below the ocean’s surface the pressure doubles. For every 1,000 feet ascent the pressure diminishes roughly one-half pound per square inch. The pressure two miles high is 9.8 pounds per square inch; at one mile high, 10.88; at three-quarters of a mile, 12.06; one-half mile, 13.33; one-quarter mile, 14.2, and at sea level, 14.7 pounds, or, in round numbers, 15 pounds per square inch.
“The unknown factor in the high altitude problem is this: Will an altiplane in one-fifth density (eight miles high), with equal push, go five times faster or one-fifth faster? The rest is a matter of simple equipment and good construction. In either case the gain is substantial. If the former were true a voyage between New York and London can be made in about three hours by going eight miles high. If the latter is true the same voyage can be made in about twelve hours running time, assuming a surface speed of 200 miles an hour, which is practically a question of power.
“To my mind it is plain that the high altitudes will be determining factors in long distance flying. Greater speed, greater distance, more comfort and less danger because when we double the time to do a risky thing we double the risk incurred; less gasolene, less weight
and expense, for if environment permits us to go 100 miles with twice the fuel we formerly used to go twenty-five miles our economic gain is obviously 100 per cent, because we may then go 100 miles with the amount of fuel we formerly consumed to go fifty miles.”
That aerial navigation at higher altitudes will undoubtedly result in great increase of speed is also the opinion of Nikola Tesla, to whom I took Mr. Mott’s conclusions in order to get the opinion of this man who has made a life-time study of the air as a medium for the transmission of electrical energy.
“In the propulsion of aerial vessels problems are involved entirely different from those presented in the navigation of the water,” said Tesla. “The atmosphere may be likened to a vast ocean, but if one imagines a submarine vessel constructed like an aeroplane one immediately realizes how inefficient it would be. The energy used in propelling a body through a medium of any kind is wasted in three different ways; first, by skin friction; second, wave making; third, production of eddies. On general principles, however, the resistance can be divided into two parts: one which is due to the friction of the medium and the other to its stickiness, or viscosity, as it is termed. The first is proportionate to the density; the second to this peculiar property of the fluid.
“Everybody will readily understand that the denser the medium the harder it is to push a body through it, but it might not be clear to every person what this other resistance — this viscosity — means. This will be understood if we compare, for instance, water and oil. The latter is lighter, but much more sticky, so that it is a greater obstacle to propulsion than water. Air is a very viscous substance and that part of resistance which is due to this quality is considerable. We must take this latter resistance into account in calculating how fast an aeroplane could fly in the upper reaches of the air.
“Now, the idea is to fly at a great height where the air is rarefied, and therefore much less power is required to propel the machine through it. If we take the pressure at sea-level at 14.7 pounds and the temperature at 15 degrees centigrade, then, without introducing several corrections that would make for greater accuracy, the pressures at different heights are about as follows: At 1,000 feet above sea-level, 14.178 lbs.; at one-mile, 12.1457 lbs.; at two miles, 10.035 lbs.; at eight miles, 3.1926 lbs.; at fifteen miles, 0.8392 lbs. and at twenty miles, 0.323 lbs.”
CONDITION EIGHT MILES UP
“According to these figures that I have worked out, at a height of eight miles the density of the air is 0.2172 or about 22-100th of that at sea level; at fifteen miles it is 0.057, and at twenty miles only 0.0219, or nearly 22-1000th of that at sea-level.
“Let us suppose then that an aeroplane rises to a height of eight miles where the pressure of the air will be only 3.1926 lbs., or, in other words, the density 0.2172 of that at sea- level. Since, as pointed out, the purely frictional resistance is proportionate to the density of the air, it is obvious that, if there were no other resistance to overcome, only about 22
per cent of power or roughly one-fifth, would be required to propel the vessel at that height, so that extremely high speed, as Mr. Mott points out, would be obtainable.
“And though the other resistance, which is due to the stickiness of the medium, will not be diminished at the same ratio, and therefore the gain will not be strictly in proportion to the decrease of density of the air, nevertheless, the total resistance will be reduced, if not to 22 per cent, perhaps to 30 per cent, so that there will be a great excess of power available for more rapid flight.
“Even allowing for the decreased thrust of the propeller due to the thinness of the air, which cannot be overcome by driving the screw faster, there still will be the very considerable gain and the aircraft will be propelled at a higher speed.
“Of course many incertitudes still exist in the theoretical treatment of a question like this, as there are a number of factors which affect the result and in regard to which we have not yet complete information.”
AT AN ALTITUDE OF TWENTY MILES
“I doubt that it will be possible to rise as high as fifteen or twenty miles, which is the opinion expressed by Mr. Mott. At the height of twenty miles there is only about 7 per cent of oxygen in the air instead of 21 per cent which is present close to the ground, and there would be great trouble in securing the oxygen supply for the combustion of the fuel, not to speak of other limitations.
“However, at a height of eight miles the decrease of oxygen can be overcome for both engine and aviator. Of course provision would have to be made for supplying the aviator and passengers with oxygen. In all probability they would have to be entirely enclosed just as a diver is enclosed. Our highest mountains are five miles and the rarefication of the air makes climbing them difficult. About five miles provision would certainly have to be made for supplying the aviator. If he were not enclosed the decrease of pressure due to the thinner air would result disastrously. The human mechanism is adjusted to a pressure of nearly 15 pounds per square inch; and if that pressure is reduced to about three pounds, as it would be at an altitude of eight miles, the aviator’s ear drums would burst, and even the blood would be forced through the pores and would ooze out of the body.”
Tesla explained that the effect would be the same as that of bringing a deep-sea fish, accustomed to live a mile below the surface, to the surface of the water. The fish simply explodes, for lack of the pressure which its body is built to withstand.
With proper protection of the aviator and an artificial supply of oxygen Tesla believes that flights at the eight-mile altitude are quite possible.
“Then there will be great progress with the lighter than air machine and we may soon expect the advent of a dirigible of the Zeppelin type as a common vehicle for travel. Contrary to the general belief, such a vessel can be propelled more rapidly than an airplane and it will be, on the whole, much safer. Furthermore it will give to the passengers the comforts that are necessary in order to make this form of travel popular. Of course in the practical use of these monstrous structures, formidable obstacles will be encountered. They are susceptible to damage by storms, and I believe also from certain danger from lightning, which will not be obviated by the use of helium gas. But I expect to see these difficulties overcome.
The dirigible, supplied with sufficient power, need not fear the storm; it can rise above it, or go around it. The only danger from storm in any case lies in being blown from the course, for while the ship is moving with the storm it is in no danger, since it travels at the same speed as the wind, and the passengers would be in absolutely quiet air, so that a candle might be lighted on deck. Methods of docking and housing the big ships must be devised, but several have been proposed that reduce the danger of landing by making it unnecessary for the ship to come to earth.”
But the revolutionizing influence on aircraft of the future Mr. Tesla believes to lie in the possibility of transmitting power to them through the air.
“For years,” he said, ” I have advocated my system of wireless transmission of power which is now perfectly practicable and I am looking confidently to its adoption and further development. In the system I have developed, distance is of absolutely no consequence. That is to say, a Zeppelin vessel would receive the same power whether it was 12,000 miles away or immediately above the power plant. The application of wireless power for aerial propulsion will do away with a great deal of complication and waste, and it is difficult to imagine that a more perfect means will ever be found to transport human beings to great distances economically. The power supply is virtually unlimited, as any number of power plants can be operated together, supplying energy to airships just as trains running on tracks are now supplied with electrical energy through rails or wires.
“The transmission of power by wireless will do away with the present necessity for carrying fuel on the airplane or airship. The motors of the plane or airship will be energized by this transmitted power, and there will be no such thing as a limitation on their radius of action, since they can pick up power at any point on the globe.
“The advance of science to this point, however, is attended with terrible risks for the world. We are facing a condition that is positively appalling if we ever permit warfare to invade the earth again. For up to the present war the main destructive force was provided by guns which are limited by the size of the projectile and the distance it can be thrown. In the future nations will fight each other thousands of miles apart. No soldier will see his enemy. In fact future wars will not be conducted by men directly but by the forces which if let loose may well destroy civilization completely. If war comes again, I look for the extensive use of self-propelled air vehicles carrying enormous charges of explosive which will be sent from any point to another to do their destructive work, with no human being aboard to guide them. The distance to which they can be sent is practically unlimited and the amount of explosive they can carry is likewise practically unlimited. It is practicable to send such an air vessel say to a distance of four or five thousand miles and so control its course either gyroscopically or electrically that it will land at the exact spot where it is intended to have it land, within a few feet, and its cargo of explosive can there be detonated.
“This cannot be done by means of the present wireless plants, but with a proper plant it can be done, and we have here the appalling prospect of a war between nations at a distance of thousands of miles, with weapons so destructive and demoralizing that the world could not endure them. That is why there must be no more war.”