EXPERIMENTS WITH A LARGE MACHINE.

Upon running my large machine over the track ([Fig. 77]) with only the main aeroplane in position, I found that a lifting effect of 3,000 to 4,000 lbs. could be obtained with a speed of 37 to 42 miles an hour. It was not always an easy matter to ascertain exactly what the lifting effect was at a given speed on account of the wind that was generally blowing. Early in my experiments, I found if I ran my machine fast enough to produce a lifting effect within 1,000 lbs. of the total weight of the machine, that it was almost sure to leave the rails if the least wind was blowing. It was, therefore, necessary for me to devise some means of keeping the machine on the track. The first plan tried was to attach some very heavy cast-iron wheels weighing with their axle-trees and connections about 11⁄2 tons. These were constructed in such a manner that the light flanged wheels supporting the machine on the steel rails could be lifted 6 inches above the track, leaving the heavy wheels still on the rails for guiding the machine. This arrangement was tried on several occasions, the machine being run fast enough to lift the forward end off the track. However, I found considerable difficulty in starting and stopping quickly on account of the great weight, and the amount of energy necessary to set such heavy wheels spinning at a high velocity. The last experiment with these wheels was made when a head wind was blowing at the rate of about 10 miles an hour. It was rather unsteady, and when the machine was running at its greatest velocity, a sudden gust lifted not only the front end, but also the heavy front wheels completely off the track, and the machine falling on soft ground was soon blown over by the wind.

I then provided a safety track of 3 × 9 Georgia pine placed about 2 feet above the steel rails, the wooden track being 30 feet gauge and the steel rails 9 feet gauge ([Fig. 77]). The machine was next furnished with four extra wheels placed on strong outriggers and adjusted in such a manner that when it had been lifted 1 inch clear of the steel rails, these extra wheels would engage the upper wooden track.[8]

[8] Springs were interposed between the machine and the axle-trees. The travel of these springs was about 4 inches; therefore, when the machine was standing still, the wheels on the outriggers were about 5 inches below the upper track.

Fig. 77.—View of the track used in my experiments. The machine was run along the steel railway which was 9 feet gauge, and was prevented from rising by the wooden track which was 35 feet gauge.

Fig. 78.—The machine on the track tied up to the dynamometer.

Fig. 79.—Two dynagraphs, one for making a diagram of the lifting effect off the main axle-tree, and the other for making a diagram of the lift off the front axle-tree. By this arrangement, I was able to ascertain the exact lifting effect at all speeds, and to arrange my aeroplanes in such a manner that the center of lifting effect was directly over the center of gravity. The paper-covered cylinders made one rotation in 2,000 feet.

When fully equipped, my large machine had five long and narrow aeroplanes projecting from each side. Those that are attached to the sides of the main aeroplanes are 27 feet long, thus bringing the total width of the machine up to 104 feet. The machine is also provided with a fore and an aft rudder made on the same general plan as the main aeroplane. When all the aeroplanes are in position, the total lifting surface is brought up to about 6,000 square feet. I have, however, never run the machine with all the planes in position. My late experiments were conducted with the main aeroplane, the fore and aft rudders, and the top and bottom side planes in position, the total area then being 4,000 square feet. With the machine thus equipped, with 600 lbs. of water in the tank and boiler and with the naphtha and three men on board, the total weight was a little less than 8,000 lbs. The first run under these conditions was made with a steam pressure of 150 lbs. to the square inch, in a dead calm, and all four of the lower wheels remained constantly on the rails, none of the wheels on the outriggers touching the upper track. The second run was made with 240 lbs. steam pressure to the square inch. On this occasion, the machine seemed to vibrate between the upper and lower tracks. About three of the top wheels were engaged at the same time, the weight on the lower steel rails being practically nil. Preparations were then made for a third run with nearly the full power of the engines. The machine was tied up to a dynamometer ([Fig. 78]), and the engines were started with a pressure of about 200 lbs. to the square inch. The gas supply was then gradually turned on with the throttle valves wide open; the pressure soon increased, and when 310 lbs. was reached, the dynamometer showed a screw thrust of 2,100 lbs.,[9] but to this must be added the incline of the track which amounts to about 64 lbs. The actual thrust was therefore 2,164 lbs. In order to keep the thrust of the screws as nearly constant as possible, I had placed a small safety valve—3⁄4-inch—in the steam pipe leading to one of the engines. This valve was adjusted in such a manner that it gave a slight puff of steam at each stroke of the engine with a pressure of 310 lbs. to the square inch, and a steady blast at 320 lbs. to the square inch. As the valves and steam passages of these engines were made very large, and as the piston speed was not excessive, I believed if the steam pressure was kept constant that the screw thrust would also remain nearly constant, because as the machine advances and the screws commence to run slightly faster, an additional quantity of steam will be called for and this could be supplied by turning on more gas. When everything was ready, with careful observers stationed on each side of the track, the order was given to let go. The enormous screw thrust started the machine so quickly that it nearly threw the engineers off their feet, and the machine bounded over the track at a great rate. Upon noticing a slight diminution in the steam pressure, I turned on more gas, when almost instantly the steam commenced to blow a steady blast from the small safety valve, showing that the pressure was at least 320 lbs. in the pipes supplying the engines with steam. Before starting on this run, the wheels that were to engage the upper track were painted, and it was the duty of one of my assistants to observe these wheels during the run, while another assistant watched the pressure gauges and dynagraphs ([Fig. 79]). The first part of the track was up a slight incline, but the machine was lifted clear of the lower rails and all of the top wheels were fully engaged on the upper track when about 600 feet had been covered. The speed rapidly increased, and when 900 feet had been covered, one of the rear axle-trees, which were of 2-inch steel tubing, doubled up ([Fig. 80]), and set the rear end of the machine completely free. The pencils ran completely across the cylinders of the dynagraphs and caught on the underneath end. The rear end of the machine being set free, raised considerably above the track and swayed. At about 1,000 feet, the left forward wheel also got clear of the upper track and shortly afterwards, the right forward wheel tore up about 100 feet of the upper track. Steam was at once shut off and the machine sank directly to the earth imbedding the wheels in the soft turf ([Figs. 81] and [82]) without leaving any other marks, showing most conclusively that the machine was completely suspended in the air before it settled to the earth. In this accident, one of the pine timbers forming the upper track went completely through the lower framework of the machine and broke a number of the tubes, but no damage was done to the machinery except a slight injury to one of the screws ([Fig. 83]).

[9] The quantity of water entering the boiler at this time was so great as to be beyond the range of the feed-water indicator.

Fig. 80.—The outrigger wheel that gave out and caused an accident with the machine.

Fig. 81.—Shows the broken planks and the wreck that they caused. It will be observed that the wheels sank directly into the ground without leaving any track.

Fig. 82.—The condition of the machine after the accident. One of the broken planks that formed the upper track is shown. It will be observed that the wheels have sunk directly into the ground without leaving any tracks, showing that the machine did not run along the ground, but came directly down when it stopped.

In my experiments with the small apparatus for ascertaining the power required to perform artificial flight, I found that the most advantageous angle for my aeroplane was 1 in 14, but when I came to make my large machine, I placed my aeroplanes at an angle of 1 in 8 so as to be able to get a great lifting effect at a moderate speed with a short run. In the experiments which led to the accident above referred to, the total lifting effect upon the machine must have been at least 10,000 lbs. All the wheels which had been previously painted and which engaged the upper track were completely cleaned of their paint and had made an impression on the wood, which clearly indicated that the load which they had been lifting was considerable.[10] Moreover, the strain necessary to double up the axle-trees was fully 1,000 lbs. each, without considering the lift on the forward axle-trees which did not give way but broke the upper track.

[10] The latest form of outrigger wheels for engaging the upper track is shown in [Fig. 84].

Fig. 83.—This shows the screw damaged by the broken planks; also a hole in the main aeroplane caused by the flying splinters.

The advantages arising from driving the aeroplanes on to new air, the inertia of which has not been disturbed, are clearly shown in these experiments. The lifting effect of the planes was 2·5 lbs. per square foot. A plane loaded at this rate will fall through the air with a velocity of 22·36 miles per hour, according to the formula √200 × P = V. But as the planes were set at an angle of 1 in 8, and as the machine travelled at the rate of 40 miles an hour, the planes only pressed the air downwards 5 miles an hour (40 ÷ 8 = 5). A fall of 5 miles an hour without advancing would only exert a pressure of ·125 lb. per square foot, according to the formula (V² × ·005 = P).[11]

[11] This is the old formula used by Haswell. The account of this experimental work was written in the autumn of 1894 and Haswell’s formula was used. I have thought best to make no changes.

Fig. 84.—This shows a form of outrigger wheels which were ultimately used.

Engineers and mathematicians who have written to prove that flying machines were impossible have generally computed the efficiency of aeroplanes moving through the air, on the basis that the lifting effect would be equal to a wind blowing against the plane at the rate at which the air was pressed down by the plane while being driven through the air. According to this system of reasoning, my 4,000 square feet of aeroplanes would have lifted only ·125 lb. per square foot, and in order to have lifted 10,000 lbs. they would have to have had an area twenty times as great. This corresponds exactly with the discrepancy which Professor Langley has found in the formula of Newton.

With aeroplanes of one-half the width of those I employed, and with a velocity twice as great, the angle could be much less, and the advantages of continually running on to fresh air would be still more manifest. With a screw thrust of 2,000 lbs., the air pressure on each square foot of the projected area of the screw blades is 21·3 lbs., while the pressure on the entire discs of the screws is 4 lbs. per square foot, which would seem to show with screws of this size, that four blades would be more efficient than two.

Fig. 85.—One pair of my compound engines. This engine weighed 310 lbs. and developed 180 H.P., with 320 lbs. of steam per square inch.

The engines, as before stated, are compound ([Fig. 85]). The area of the high-pressure piston is 20 square inches, and that of the low-pressure piston is 50·26 square inches. Both have a stroke of 12 inches. With a boiler pressure of 320 lbs., the pressure on the low-pressure piston is 125 lbs. to the square inch. This abnormally high pressure in the low-pressure cylinder is due to the fact that there is a very large amount of clearance in the high-pressure cylinder to prevent shock in case water should go over when the machine pitches; moreover, the steam in the high-pressure cylinder is cut off at three-quarters stroke, while the steam in the low-pressure cylinder is cut off at five-eighths stroke. If we should compute the power of these engines with the steam entering at full stroke, without any friction, and with no back pressure on the low-pressure cylinder, the total horse-power would foot up to 461·36 horse-power at the speed at which the engines were run—namely, 375 turns per minute. If we compute the actual power consumed by the screws, by multiplying their thrust, which is probably 2,000 lbs. while they are travelling, by their pitch, 16 feet, and this by the number of turns which they make in a minute, and then divide the product by 33,000,

2,000 × 16 × 37533,000 = 363·63,

we find that we have 363·63 horse-power in actual effect delivered on the screws of the machine, which shows that there is rather less than 22 per cent. loss in the engines, due to cutting off before the end of the stroke, to back pressure, and to friction. The actual power applied to the machine being 363·63 horse-power, it is interesting to know what becomes of it. When the machine has advanced 40 miles (which it would do in an hour), the screws have travelled 68·1 miles (375 × 16 × 605,280) = 68·1; therefore, 150 horse-power is wasted in slip, and 213·63 horse-power consumed in driving the machine through the air. Now, as the planes are set at an angle of 1 in 8, the power actually used in lifting the machine is 133·33, and the loss in driving the body of the machine, its framework and wires through the air is 90·30 horse-power.

Powerlost inscrew slip,150 H.P.
„„driving machinery and framework,80·30„
„actually consumed in lifting the machine,133·33„
Total power delivered by the engines,363·63„