Читать книгу The Rise of the Flying Machine - Hugo Byttebier - Страница 34

Hiram Maxim

Maxim started work on a real flying machine in 1889. In contrast to Ader’s secretiveness, Maxim was quite outspoken about his experiments. He regularly wrote articles in several magazines, talked freely about his projects and engaged in an extensive correspondence with Octave Chanute. Because of this, everybody who was interested knew how Maxim was getting on with solving the problems of human flight and it was easy to follow the progress of the construction of his aeroplane and of the tests he was carrying out.

By 1891, the machine had taken shape. It consisted of a steel construction which carried a huge rectangular wing of low aspect ratio which was built as a frame of steel tubes covered in silk. The wing was 110 ft long and 40 ft wide and, when completed, Maxim’s flying machine reached a length of 145 ft, the same length, curiously enough as Henson’s projected aeroplane of 1843.

At the sides of the machine four smaller wings of high aspect ratio projected outwards from the main frame. These small wings were set at a pronounced dihedral angle and were “used for keeping the equilibrium correct”. This meant that the machine was designed with inherent lateral stability because the small outside wings remained fixed as no ailerons or other artifices for changing the lateral position were provided. When the small stabilizing wings were attached, the machine looked like a huge biplane but the main wing consisted of the single 4,400 sq ft monoplane canvas. Its total wing surface was 5,550 sq ft.

The final completion of the machine was delayed because of Maxim’s manifold other activities and his constant trips to the US and also because of the work which was being carried out on the powerplant.

In fact, the most important part of a heavier-than-air flying machine is the powerplant and Maxim devoted much time and ingenuity to developing it. When finished, it was one of the wonders of its time. From a great quantity of steel tubes which had to be imported from France, Maxim built an enormous flash steam generator heated by an extraordinary number of jets (45,000 on the first design, later reduced to 7,500) which burned an inflammable mixture of naphtha and air. The generator was built for a steam pressure of 400 lbs/sq in., although in practice the maximum pressure used was 320 lbs/sq in. (Ader used a maximum of 220 lbs/sq in.). The steam, under high pressure, fed two big compound engines which at 375 rpm developed about 180 hp each. A condenser was included and the total weight of the machinery amounted to 1,800 lbs. When the necessary amounts of fuel and water were added, as well as the weight of three men who were to be on board, the total weight amounted to something over 5,000 lbs.

The first tests saw the machine rolling over a 1,800 foot long railway track with a 9 ft gauge laid out in his Baldwyn Park estate and, in order to prevent the craft from becoming airborne before its time, a heavy rolling railtruck was used to hold it down, adding another 3,000 lbs to the total weight.

In June 1892, Maxim published an article in which he explained how his machine was to be steered up or down. He wrote: “We should attach two long arms to our aeroplane in such a manner that they would project a considerable distance in the 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 if 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.”

Maxim was obviously more concerned with control than with stability in the longitudinal sense because, when the machine was ready, it effectively possessed two movable horizontal rudders (or elevators) one in front and one to the rear. For steering to the left or right a difference in the rotational speed of the airscrews was to be used and it is possible that this idea influenced Ader to some extent when he decided upon the use of his twin propellers on the “Avion III” of 1897.

The first rolling tests of Maxim’s flying machine were auspicious. It soon became clear that more than sufficient power was available because the craft could be accelerated to over 40 mph, more than enough to lift a craft loaded at 1 lbs/sq in. into the air. Maxim soon found that his machine was not only capable of lifting but that it was also incapable of being kept to the ground even when the heavy 3,000 lbs railcar was added to it and on one occasion during an experimental run in 1893 a sudden gust of wind lifted the plane off the ground, much to the alarm of the men aboard.

Maxim added another restraining device, which consisted of a double row of planks 30 ft apart and two ft above the ground. The machine was then fitted with outriggers carrying wheels that would come into contact with the planks from below as soon as the aeroplane rose more than the permitted two feet.

Experiments were then continued with increased boiler pressures, and consequently increased speeds, until on 31 July 1894, the pressure was raised to 320 lbs, which was calculated to be the equivalent of 365 hp. After a run of 600 ft, all the upper wheels were pushing against the restraining planks and after a further 300 ft the push became so great that one of the outrigger axles doubled up, a plank broke and the plane became free at the rear, causing even more alarm than the first time. Maxim quickly cut off steam and the plane settled down again, although rather badly damaged.

Maxim was now at the point where free flight could be contemplated, a flight which in 1892 he had imagined could be as follows: “Taking one man with us to attend to the two horizontal rudders and to keep the machine on an even keel, we should make our first flight, running the engines and doing the right and left steering ourselves. A day should be selected when there is a fresh breeze of about 10 mph. 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 mph. This would lift the machine off the track and probably slightly change the centre of effort. This, however, would be quickly corrected by the man at the wheel. While the machine is still in the air careful experiments should be tried in regard to the action of the rudders... 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...”

“A large field as near to 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 mph. If the wind were blowing at the rate of 20 mph the machine would approach the earth very gradually indeed, so that all shock would be avoided. It would only require a few yards of comparatively smooth ground to run after alighting, in order that there should be no disagreeable shock or danger.”

This was not an inaccurate description of an actual flight, although the landing speed of 20 mph was a bit on the low side, but no free flight was ever attempted, certainly not after the crash of 31 July 1894.

“A hundred necks have to be broken, before all sources of accident can be ascertained and guarded against” wrote Cayley in 1846 with his usual acumen. Maxim did not offer his own neck to be the first. He had become aware of the fact that a free flight might possibly not be such an easy affair as he had suggested in 1892 and it was as well that he did not press his experiments any further.

Maxim’s flying machine, with its two movable rudders was, like Ader’s, longitudinally unstable and had to depend on the continuous intervention of a man at the wheel or wheels to actuate those rudders and, however quickly he tried to correct the balance, it would soon have been beyond that man’s capacity. For a time Maxim toyed with the idea of installing a gyrostat for automatic balancing, but he decided to let the matter drop.

In the evolution of the heavier-than-air flying machine, Maxim was the first to take off under his own power and also the first to produce sufficient power to achieve the feat and, although his craft never actually made a completely free flight, it did fly.

The cost of his experiments has been estimated at $200,000. After the accident of 1894, the plane was repaired and Maxim made several more runs, although he never left the boundary of the restraining upper planks, and limited the steam pressure to the extent that this restraining mode of flight could be made with safety.

He later continued to work, to invent, to write and to lecture, and in general took the necessary steps to ensure that posterity would not forget him, and in this he was certainly successful.