Artificial and Natural Flight

by Hiram S. Maxim

RECAPITULATION OF EARLY EXPERIMENTS.

Fig. 74.—Photograph of a model of my machine, showing the fore and aft horizontal rudders and the superposed aeroplanes.

In my early “whirling table”[5] experiments, the aeroplanes used were from 6 inches to 4 feet in width. They were for the most part made of thin pine, being slightly concave on the underneath side and convex on the top, both the fore and aft edges being very sharp. I generally mounted them at an angle of 1 in 14[6]—that is, in such a position that in advancing 14 feet they pressed the air down 1 foot. With this arrangement, I found that with a screw thrust of 5 lbs. the aeroplane would lift 5 × 14, or 70 lbs., while if the same plane was mounted at an angle of 1 in 10, the lifting effect was almost 50 lbs. (5 × 10). This demonstrated that the skin friction on these very sharp, smooth and well-made aeroplanes was so small a factor as not to be considered. When, however, there was the least irregularity in the shape of the aeroplane, the lifting effect, when considered in terms of screw thrust, was greatly diminished. With a well-made wooden plane placed at an angle of 1 in 14, I was able to carry as much as 113 lbs. to the H.P., whereas with an aeroplane consisting of a wooden frame covered with a cotton fabric ([Fig. 75]), I was only able to carry 40 lbs. to the H.P.[7]

[5] A name given by Professor Langley to an apparatus consisting of a long rotating arm to which objects to be tested are attached.

[6] I found it more convenient to express the angle in this manner than in degrees.

[7] The actual power consumed by the aeroplane itself was arrived at as follows:—The testing machine was run at the desired speed without the aeroplane, and the screw thrust and the power consumed carefully noted. The aeroplane was then attached and the machine again run at the same speed. The difference between the two readings gave the power consumed by the aeroplane.

Fig. 75.—The fabric-covered aeroplane experimented with. The efficiency of this aeroplane was only 40 per cent. of that of a well-made wooden aeroplane.

Fig. 76.—The forward rudder of my large machine, showing the fabric attached to the lower side. The top was also covered with fabric. This rudder considered as an aeroplane had a very high efficiency and worked very well indeed.

These facts taken into consideration with my other experiments with large aeroplanes, demonstrated to my mind that it would not be a very easy matter to make a large and efficient aeroplane. If I obtained the necessary rigidity by making it of boards, it would be vastly too heavy for the purpose, while if I obtained the necessary lightness by making the framework of steel and covering it with a silk or cotton fabric in the usual way, the distortion would be so great that it would require altogether too much power to propel it through the air. I therefore decided on making a completely new form of aeroplane. I constructed a large steel framework arranged in such a manner that the fore and aft edges consisted of tightly drawn steel wires. This framework was provided with a number of light wooden longitudinal trusses, similar to those shown in [Fig. 76]. The bottom side was then covered with balloon fabric secured at the edges, and also by two longitudinal lines of lacing through the centre. It was stretched very tightly and slightly varnished, but not sufficiently to make it absolutely air-tight. The top of this framework was covered with the same kind of material, but varnished so as to make it absolutely airtight. The top and bottom were then laced together forming very sharp fore and aft edges, and the top side was firmly secured to the light wooden trusses before referred to. Upon running this aeroplane, I found that a certain quantity of air passed through the lower side and set up a pressure between the upper and lower coverings. The imprisoned air pressed the top covering upward, forming longitudinal corrugations which did not offer any perceptible resistance to the air, whereas the bottom fabric, having practically the same pressure on both sides, was not distorted in the least. This aeroplane was found to be nearly as efficient as it would have been had it been carved out of a solid piece of wood. It will be seen by the illustration that this large or main aeroplane is practically octagonal in shape, its greatest width being 50 feet, and the total area 1,500 square feet.