Having thus designed and built his apparatus, the next point for M. Maxim to consider was how to get it up into the air, how to control it while sailing. and how to alight with it safely. To this he has evidently given much thought, and in an article published by him in the Cosmopolitan Magazine for June, 1892 he thus describes what course he would pursue if a sum of $100,000 were placed at his disposal, for constructing and experimenting a successful flying machine; which course seems to be so carefully planned that we may fairly assume that it is the one determined upon by M. Maxim for experiments with his own actual machine.
"The machine should be run around the one-mile track at all speeds, from 20 miles per hour to 100 miles per hour, and the power actually required should be carefully noted. These runs would enable us to ascertain how our pumps worked at high speed. and how much our screws pushed, and if we put a brake to the wheels we should find out the slip of the screws. We could also ascertain the efficiency of our condenser at various speeds, and the temperature of the water could be taken. In order to run on a railway track, the machine, of course, must be provided with wheels, and two sets of these would be necessary; one set should be of great weight, so as to hold the machine down when running on the track. and the other set should be light, for actual flying. Springs should be interposed between the axle trees and the machine, after the manner of railway carriages, and there should be attached above each wheel some sort of an index or indicator to show the exact load resting on each wheel. When all the parts of the machine had been made to operate smoothly and satisfactorily, the silk could be placed on the aeroplanes, and then our serious experiments might be said to commence.
"We should first begin by running slowly--say at the rate of 20 miles per hour--and carefully note the lift on the indexes over each wheel. If we found that with a speed of 20 miles an hour, three fourths of the load was lifted off the forward axletree, and only one-fourth off the hind one, then we should change the center of weight further forward, so as to bring it as near as possible under the center of effort or lift. We should then make another trial and if we found that the lift was equal both fore and aft we should increase the speed very carefully, gradually observing the lift at the four corners of the machine, until the whole weight of the machine was supported by the aeroplane, and the whole weight of the wheels (about one ton) by the railway track. Then, when there was neither lift nor load on either wheel, we might consider that we had arrived at a stage in our experiments where we could turn our attention to the subject of steering.
"A boat has to be steered in only one direction--namely, a horizontal direction, to the right or to the left. A locomotive torpedo or a flying machine must be steered in two directions--right or left, or up or down. We should experiment with the more difficult one at first--namely, the up and down or vertical direction. We should attach two long arms to our aeroplane in such a manner that they would project a considerable distance in she rear of the machine. To these arms we should pivot a very large and light silk-covered rudder and connect it with ropes, so that it could be turned up or down by a small windlass from the machine. We should then take a run on the track and see it the changing the angle of this rudder would increase or diminish the load on the forward or hind wheels. If we found that it would do this, but not sufficiently so, we should attach another rudder in exactly the same manner to the forward end of the machine. Suppose that, at a speed of 35 miles per hour, with both rudders set at the same angle as the aeroplane, we should find that the whole weight of the machine was carried by the aeroplane and the whole weight of the wheels (2,000 lbs.) by the track, we could then consider that the adjustment of our load was correct, and that the center of weight was directly under the center of effort for a speed of 35 miles an hour. We should then elevate the front edge of the forward rudder and depress the front edge of the rear rudder; this would cause the machine to lift on the forward axletree and the rear end of the machine to press on the hind axletree. If we found by changing the angle of the rudders that the load could be increased or diminished on either axle tree to the extent of 15 5 per cent. of our whole load we could consider that this phase of the problem was solved.
"For horizontal steering we should try first the effect of the screws. There should be a three-way valve in the steam pipe connected with a lever, so that we should be able to partly close off the steam from the engine of one screw, and turn more steam on to the other. This would probably be all that would be found necessary; if not, we should try rudders.
"To prevent the machine from swaying in the air, the aeroplane should so be constructed that no matter in which direction it tilted it would diminish the lifting power of the lifted part and increase the lifting power of the depressed part. This (diedral side wings) would be simple and automatic; moreover, the stability of the machine could be still further increased by having the center of gravity much below the center of lift.
"Having all things in readiness, the heavy wheels should be removed and the light ones put on; and taking one man with us to attend to the two horizontal rudder and to keep the machine on an even keel,41 we should take our first fly, running the engines and doing the right and left steering ourselves. A day should be selected when there was a fresh breeze of about 10 miles per hour. We should first travel slowly around the circular railway until we came near that part of the track in which we should face the wind. The speed should then be increased until it attained a velocity of 38 or 40 miles an hour. This would lift the machine off the track and probably would slightly change the center of effort. This, however, would be quickly corrected by the man at the wheel. While the machine was still in the air careful experiments should be tried in regard to the action of the rudders; it should be ascertained to what degree they had to be tilted in order to produce the desired effect on the machine. The machine should also be run at a speed less than 35 miles per hour in order to allow it to approach the earth gradually; then the speed should be increased again to more than 35 miles an hour in order to rise, at the same time trying the effect of running one propeller faster than the other, to ascertain to what extent this would have to be done in order to cause the machine to turn to the right or to the left. If the machine should be constructed so that each particular foot of its surface carried a load of 1 lb. 2 oz., and if we should stop the engine dead and allow the machine to fall, it would approach the earth at a speed of 15 miles an hour. or one mile in four minutes. This evidently would cause a considerable shock, and unless there was a good deal of elasticity to the parts and a good deal of travel between the axletrees and the machine, the shock would probably be sufficient to distort or injure. some part of the light structure. But it is not necessary to approach the earth directly. Professor Langley found in his experiments that when a horizontal plane was travelling rapidly through the air, it approached the earth as though it were 'settling through jelly.'
"A large field as near our railway as possible should be selected for alighting, and having approached the field so as to be facing the wind, we should gradually descend by slowing up the engines, and finally alight while the machine was still advancing at the rate of 20 miles an hour. If the wind should be blowing at the rate of to miles an hour the machine would approach the earth very gradually indeed, so that all shock would he avoided. It would only require a few yards of comparatively smooth ground to run on after alighting, in order that there should be no disagreeable shock or danger.
"The cost of these experiments would be from $50,000 to $100,000, and the time required would be two years."
It will be noted how complicated and delicate these various adjustments must necessarily be, and how many different parts must be made to do their work perfectly before it can be safe to venture into the air. The aeroplane surfaces must be prevented from altering their shapes at varying speeds, the rudders must be made to maintain the course automatically, the engine must be governed as to speed, the boiler and gas-jet flames must be regulated by the consumption of steam, and the condenser must be efficient at all temperatures of the air, as well as at all speeds. Moreover, and most important, no part must break under varying strains, and the equilibrium must be maintained.
These are formidable and yet indispensable requirements, well calculated to appall the boldest inventor; for while with an experimental model an accident is of little consequence and is easily repaired, with an actual flying machine an accident will probably prove disastrous, even if the inventor does not lose his life.
M. Maxim, therefore, has acted most wisely in taking plenty of time and in testing his apparatus in every way before venturing to leave tile ground with it. Having completed it so that it was ready for the hazard of actual trial, he next experimented with it under conditions of comparative safety, and opened up the chapter of accidents.
The first difficulty he met with occurred through the breaking of some of the wire stays. These had been made of steel high in carbon in order to secure great tensile strength, and they proved brittle. From a private letter from M. Maxim dated October 6, 1892 the writer is permitted to give the following extract, which gives also a most interesting and hitherto unpublished description of the steam-engine and boiler, which constitute thus far the great achievement of M. Maxim:
The steam generator is constructed somewhat on the Thorneycroft principle, except that the tubes are much lighter and thinner and have a greater number of sinuosities in them. In the Thorneycroft boiler the distributing water tubes at the bottom are of considerable size and of great weight. In my engine they are only 2 1/2 in. in diameter and Ii mm. in thickness. The downtake for the water is only 3 in. in diameter, and instead of having two, as with the Thorneycroft boiler, there is one, which branches off like the inverted letter Y. In the Thorneycroft boiler the difference in gravity of the water in the hot interior tubes and in the two external ones, which are not heated. is the only means of keeping up the circulation; but as all the passage-ways for water are very large, this is sufficient.
Suppose that in my system I am using steam at 300 lbs. pressure to the square inch; I have my water at a pressure of 335 lbs. to the square inch, and the water escapes through a species of automatic injector, and in falling 35 lbs. in pressure does a certain amount of work on the surrounding water The cold water going in from the pump is therefore made to combine with the hot water in the downtake. This increases the gravity of the water and at the same time causes a very rapid forced circulation. No matter to what extent the fire may be forced, the water has to go through in any event. All the water that is coming in from the pump, as well as all of the water that it takes along with it from the top separating drum, from which the steam is taken, is forced through the hot tubes. The nozzle through which the incoming water escapes from the higher to the lower pressure is provided with a spring, which always keeps a difference in pressure of about 35 Ib .; whether the quantity of water pressing in is large or small, the difference is always the same. A very convenient apparatus is attached to the teed water pipe, by which it is possible to see at a glance exactly how many pounds of water per hour are entering the boiler. Directly over the boiler proper there is another series of very small copper tubes through which the water passes before entering the boiler proper, therefore products of combustion, after passing between the tubes of the boiler. are brought in contact with the incoming water before escaping. This so reduces the temperature of the escaping products of combustion that Brunswick black or linseed-oil are not burned off the smoke-stack.
For a fuel I employ naphtha of 72° Beaume. This napbtha is pumped into a small vertical boiler heated with a part of its own contents.
The vapors from the boiler are led directly to an air injector, where they escape under a pressure of 35 lbs. to the square inch. The mixture of air and gas is then burned through rather more than 6,ooo gas jets under the boiler. Steam might be also mixed if required. The distributing of the flame is very even, and it is possible to fill the whole fire-box with a purple flame. The regulating of the supply of naphtha is controlled by the weight of the gas generator; if the weight of the generator is too great, it operates upon a ratchet, which shortens the stroke of the pump; if it is too light, a spring raises the generator and its contents, when the ratchet operates in a contrary direction and increases the stroke of the pump. In this way the quantity of naphtha in the boiler is kept constant. The fire is regulated not only by the pressure in the boiler, but by a thermostatic regulator also. The feed-water pump is also regulated by changing the length of the stroke.
The engines are compound, and have a peculiar arrangement placed in a connection between the high and low-pressure cylinders in such a manner that if the pressure in the boiler rises above 300 lbs. to the square inch the steam is shunted past the high-pressure cylinder and enters the low-pressure cylinder, and it is arranged in such a manner that the pressure of steam falling from 300 lbs. to 100 lbs. does a certain amount of work on the exhaust steam that is passing through the high-pressure cylinder after the manner of an injector-that is to say, the escaping force of the steam reduces the back pressure on the high-pressure cylinder and increases the pressure on the low pressure piston.
With two screws, each 17 ft. 10 in. in diameter, and with 300 lbs. pressure to the square inch, the machine has been made to pull on a dynamometer 1,960 lbs. If we multiply this pull by the number of lures per minute that the engine makes, and by the pitch of the screws, we find that the engines develop 300 horse power.
The complete weight of engines, boilers, pumps, generators, condensers, and the weight of water in the complete circulation. amounts to 8 lbs to the horse power, and this of itself I consider quite an achievement.
The spread of the wings of the machine is 107 ft., and the total length from the point of the forward rudder to the rear end of the after rudder is about zoo ft. Beneath the main aeroplane there is a considerable number of narrow planes superposed, which extend outward to nearly the full width of the machine. So far, trials have only commenced with the main aeroplane, which is 50 ft. wide and 45 ft. long in the direction of the length of the machine.
The whole machine is mounted on steel wheels 8-ft. gauge, and springs are interposed between the machine and the axietrees, both forward and back axletrees are attached to a dynagraph, which makes a diagram of the lift of the machine as it advances upon the track. The drum which holds the paper turns once round in 1,800 ft., and whatever the machine lifts either forward or back is recorded upon the paper drum. One of the drums is also provided with a pencil, which makes a diagram of the speed at which the machine is traveling.
I am very much hampered, however, for room; there is very little clear space between the trees, and to obtain adjoining premises without trees costs a prohibitive sum. What I should have is a circular or oval track, which would be a mile long. When the experiments are tried with a side wind blowing five miles an hour, a lift of one ton has been recorded on one side of the machine while the other side would not lift over 100 lbs.
The whole machine, when loaded, will weigh about 7000 lbs., so you will see if the machine will lift anything like as much, per pound of push. as I succeeded in lifting with my first apparatus, it will be sure to go.
However, I find that a great number of steel stays are necessary in order to hold the machine in shape, and while these do not weigh much, they appear to offer a considerable resistance to the passage of the machine through the air. If I were to build another machine I should aim more at getting less atmosheric resistance, because I can see now that everything else is assured except this single factor. If the machine does not go it will simply be because too much force is expended in driving the framework through the air.
Work has been greatly delayed, in the first place, because I was absent from England a great deal, and, in the second place, we have had several serious accidents. The high-class steel wires-plow rope--which are used for stays are not always reliable. On two occasions these wires have broken, and becoming entangled in the wheels, have made a complete wreck of the wheels and everything about them. The last breakdown will take about a month to repair, and I shall put in a lower class of steel in all the stays that are near the wheels.
This damage was duly repaired, and the experiments were resumed early in 1893. In one of these, with a spread of somewhat more than half of the sustaining surface which the apparatus is designed to carry in full flight, M. Maxim succeeded in obtaining, at a speed of 25 miles per hour and with a thrust of the screws of 1,000 lbs, a lift over the front wheels of 2,300 lbs., and over the hind wheels of 1,900 lbs., as recorded by the dynagraphs. On a subsequent run, after making some alterations, he succeeded in obtaining, at a speed of 27 miles per hour and with a thrust of screws of only 700 lbs., a lift over the front wheels of 2500 lbs., or quite all the weight resting on them and of 2,800 lbs. over the hind wheels; thus showing a total lift of 7 57 lbs. per pound of thrust, as against 4.20 lbs. lifted per pound of thrust on the former occasion.
M. Maxim published the diagrams illustrating both these runs (and still another subsequently made) in the London Engineer for March 17, 1893 and gave a description in which he stated that the principal lift was obtained from the large aeroplane of 2894 sq. ft. in area.
The run last above described was made on February 16 1893 and on the same day two more runs were made until stopped by an accident.
First, an additional pair of wheels was attached under the front end of the machine, connected in such a manner that the small and lighter wheels could lift 3 in. from the track. Three men were also placed over the forward axletree. and a run was then made with 900 lbs. pull on the dynamometer. After the machine had run about 400 ft. the light wheels lifted clear of the track, and when the engines were stopped they came back to the track all right. The machine was then run again with 1000 lbs. pull on the dynamometer, with the following result, described in a letter to the writer from M. Maxim dated February 21 1893:
I have had another accident with my apparatus.
My main aeroplane is 50 ft. wide and 47 ft. long in the direction in which the machine travels. I had another aeroplane directly in front of the engine, which was about 18 ft. long and 4 ft. wide. On the first runs which I had been making I found a great deal of atmospheric resistance which I could not account for except that it resulted from the bagging of the main aeroplane and the resistance offered by the numerous struts and wires which I used in my attempts to keep it approximately flat. With the engines running at a sufficient speed to give a push of 1325 lbs., it was found that the lift on the aeroplane did not much exceed the push of the screws.
I then made a radical change in the manner of holding the plane flat and tried my first experiments after this with a push of 800 lbs., when it was found that the lift was a great deal more than it was with the 1.325 lbs. in the previous experiments; in fact, the lift on the front pair of wheels was equal to the weight resting on these wheels, and the machine was only kept from leaving the track by the weight of three men whom I carried directly over the front axletree. This I regarded as dangerous. I then attached two very large cast-iron wheels in such a manner that the light wheels could lift some inches from the track before the heavy wheels were lifted at all, the weight of the heavy wheels and their axletree being about 1,400 lbs. Three men were also added to this load.
In making the run the gas was carefully turned on until the engines gave a push of 1000 lbs. I had noticed that as the machine advanced and the engine ran faster, the boiler pressure was diminished. I therefore, upon starting, turned on a little more gas, so that the pressure, instead of falling, increased slightly during the run. When about 400 ft. had been covered, the two front wheels lifted off the track, leaving the heavy wheels still on the track; but just before stopping the heavy iron wheels also lifted from the track, and when the engines were' slopped one of the wheels got into the soft earth, sinking down and tilting the machine over to one side. A gust of wind then tipped the machine on its side; but the breaking, which was confined almost entirely to the framework for holding the cloth. was caused by the impetuosity of a lot of men who tugged away at my ropes, and putting a strain downward instead of upward on the ropes, succeeded in completely destroying the framework.
The speed was 27 miles an hour, and the pressure of steam about 200 lbs. The lift recorded was nearly 6,000 lbs., as shown by the diagrams taken from the dynographs. The incline of the main aeroplane was, however, very steep, being about 1 in 9.
The lift was more than I expected. I did not think that a plane so very large, especially in the direction in which it was traveling, would be so efficient. I thought I should have to depend more on the narrow planes which extend beyond the main plane. This more than expected lift, however, may have been due to the wind, during the last end of the run, being contrary to the direction in which the machine was traveling.
I think that these experiments demonstrate that an aeroplane may be made to carry a considerable load.
It will take some time to repair the damage. None of the expensive machinery was damaged in the least. I shall take greater care in the future not to experiment when there is a liability to squalls, and shall have a fender so that if the machine gets off the track it will not topple over.
It is understood that at the time this run was made about half of all the sails were in position--namely, 3160 sq. ft. The power which the engines developed was about half of their full power, so that it will be realized that there will be ample lifting power when free flight is attempted.
Since then the apparatus has been repaired, and in an article which has been extensively published in American newspapers, a correspondent, writing under date of London, September 12 1893 gives an account of a ride which he took on the machine. After describing it and the house in which it is sheltered, he says:
I mounted the platform, made of light matched boards so thin that they seemed scarcely able to bear a man's weight. Prior to the start a rope running to a dynamometer and pose was attached behind, to measure the forward impulse or push of the screws. . . . The action of the screws caused very little shaking through the whole machine, and this was a surprise to me, comparing the tremendous force with the delicate framework. Behind the ship, 10 ft. away, two men were shouting from the dynamometer and indicating the degree of push on a large board for the engineer to read. The index quickly marked in succession 400, 500, 600, 700, and finally 1200 lbs. of push, and then the commander yelled, "Let go!" A rope was pulled, and then the machine shot forward like a railway locomotive, and with the big wheels whirling, the steam hissing, and the waste pipes puffing and gurgling, flew over the 1,800 ft. of track. It was stopped by a couple of ropes stretched across the track working on capstans fitted with reverse fans. The stoppage was quite gentle. The ship was then pushed back over the track by the men, it not being built, any more than a bird, to fly backward.
M. Maxim is quoted by the correspondent as saying, among other things, concerning his apparatus:
Propulsion and lifting are solved problems; the rest is a mere matter of time. . . . Haste in such a venture is the worst of policies. Weak points must be thoroughly sought for, and everything made completely safe before the public is invited to consider the air-ship as a practical means of transit. I am looking for a location with more room for me to experiment than I can find in England. I am cramped here for want of space.
Such is the present status (1893) of this bold and costly attempt to solve the problem of aviation with an aeroplane. M. Maxim as he says himself, may not achieve final success; but he has, in the opinion of the writer, very greatly advanced the chances of eventual success. He has constructed, it may be said invented, a steam engine with its adjunct developing 300 horse power, and weighing only 8 lbs. to the horse power--an achievement hitherto unparalleled, and probably the most important problem to solve before man can hope to succeed in navigating the air at will.
There doubtless remain other problems to be worked out practically, notably that of effectually controlling a flying machine while in the air, both in the vertical and the horizontal direction; that of maintaining the equilibrium under all circumstances of speed and angles of incidence, and also those of devising methods of starting up and of alighting safely anywhere; for in practical operation, even for war purposes, M. Maxim's machine cannot always be brought back to get a start upon its initial railway track.
There probably also remain some questions to be settled as to the best forms, extent and texture of the supporting surfaces; and it is not impossible that his experiments will eventually lead M. Maxim to a complete remodeling of his aeroplanes; but, as has been pointed out in discussing "screws to lift and propel," it is already within his power, by reason of his marvelously light steam-engine, to go up into the air with an aerial screw, and to perform therein various evolutions.
In any event, the name of M. Maxim must ever remain as that of one of the men who have hitherto done most to advance the solution of the problem of aviation.
41 M. Maxim
has since added the gyrostat.
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