Artificial and Natural Flight

by Hiram S. Maxim

The great advances that have been made of late years in electrical science and engineering have led many to believe that almost any knotty scientific question may be solved by the employment of electrical engineering, and a great deal has been written and said in regard to navigating the air by flying machines driven by electric motors.

Before I commenced my experiments, I made enquiries of all the prominent electrical engineering establishments where there was any likelihood of obtaining light and efficient electric motors, and found that it was impossible to obtain one that would develop a horse-power for any considerable time that would weigh less than 150 lbs. Since that time, notwithstanding that a great deal has appeared in the public prints about the efficiency and lightness of electric motors, I am unable to learn of any concern that is ready to furnish a complete motor, including a primary battery, which would supply the necessary current for two hours at a time, at a weight of less than 150 lbs. per horse-power, and as far as I have been able to ascertain from what I have myself seen, I cannot learn that there are any motors in practical use which do not weigh, including their storage batteries, at least 300 lbs. per horse-power. The last electric motor which I examined was in a boat; it was driven by a primary battery which weighed over 1,000 lbs. to the horse-power. From this I am of the opinion that we cannot at present look to electricity with any hope of finding a motor which is suitable for the purpose of aerial navigation.

ENGINES.

There is no question but what birds, and for that matter all animals, when considered as thermo-dynamic machines, are very perfect motors; they develop the full theoretical amount of energy of the carbon consumed. This we are quite unable to do with any artificial machine, but birds, for the most part, have to content themselves with food which is not very rich in carbon. It is quite true that a bird may develop from ten to fifteen times as much power from the carbon consumed as can be developed by the best steam engine, but, as an off-set against this, a steam engine is able to consume petroleum, which has at least twenty times as many thermal units per pound as the ordinary food of birds. The movement of a bird’s wings, from long years of development, has without doubt attained a great degree of perfection. Birds are able to scull themselves through the air with very little loss of energy. To imitate by mechanical means, the exact and delicate motion of their wings would certainly be a very difficult task, and I do not believe that we should attempt it in constructing an artificial flying machine. In Nature it is necessary that an animal should be made all in one piece. It is, therefore, quite out of the question that any part or parts should revolve. For land animals there is no question but what legs are the most perfect system possible, but in terrestrial locomotion by machinery, not necessarily in one piece, wheels are found to be much more effective and efficient. The swiftest animal can only travel for a minute of time at half the speed of a locomotive, while the locomotive is able to maintain its much greater speed for many hours at a time. The largest land animals only weigh about 5 tons, while the largest locomotives weigh from 60 to 80 tons. In the sea, the largest animal weighs about 75 tons, while the ordinary Atlantic liner weighs from 4,000 to 14,000 tons. The whale, no doubt, is able to maintain a high speed for several hours at a time, but the modern steamer is able to maintain a still higher speed for many consecutive days.

As artificial machines for terrestrial and aquatic locomotion have been made immensely stronger and larger than land or water animals, so with flying machines, it will be necessary to construct them much heavier and stronger than the largest bird. If one should attempt to propel such a machine with wings, it would be quite as difficult a problem to solve as it would be to make a locomotive that would walk on legs. What is required in a flying machine is something to which a very large amount of power can be directly and continuously applied without any intervening levers or joints, and this we find in the screw propeller.

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When the Brayton gas engine first made its appearance, I commenced drawings of a flying machine, using a modification of the Brayton motor which I designed expressly for the purpose; but even this was found to be too heavy, and it was not until after I had abandoned the vertical screw system that it was possible for me to design a machine which, in theory, ought to fly. The next machine which I considered was on the kite or aeroplane system. This was also to be driven by an oil engine. Oil engines at that time were not so simple as now, and, moreover, the system of ignition was very heavy, cumbersome, and uncertain. Since that time, however, gas and oil engines have been very much improved, and the ignition tube which is almost universally used has greatly simplified the ignition, so that at the present time, I am of the opinion that an oil engine might be designed which would be suitable for the purpose.

In 1889 I had my attention drawn to some very thin, strong, and comparatively cheap tubes which were being made in France, and it was only after I had seen these tubes that I seriously considered the question of making a flying machine. I obtained a large quantity of them and found that they were very light, that they would stand enormously high pressures, and generate a very large quantity of steam. Upon going into a mathematical calculation of the whole subject, I found that it would be possible to make a machine on the aeroplane system, driven by a steam engine, which would be sufficiently strong to lift itself into the air. I first made drawings of a steam engine, and a pair of these engines was afterwards made. These engines are constructed, for the most part, of a very high grade of cast steel, the cylinders being only ³⁄₃₂ of an inch thick, the crank shafts hollow, and every part as strong and light as possible. They are compound, each having a high-pressure piston with an area of 20 square inches, a low-pressure piston of 50·26 square inches, and a common stroke of 1 foot. When first finished, they were found to weigh 300 lbs. each; but after putting on the oil cups, felting, painting, and making some slight alterations, the weight was brought up to 320 lbs. each, or a total of 640 lbs. for the two engines, which have since developed 362 horse-power with a steam pressure of 320 lbs. per square inch. A photograph of one of these engines is shown in [Fig. 85].

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