PART I: THE EVOLUTION OF THE AEROPLANE

IV. THE MIDDLE NINETEENTH CENTURY ( Page 5) < Previous     Next >

Continued from page 4......
'The planes were staid from three sets of fish-shaped masts, and rigged square and firm by flat steel rigging. The engine and boiler were put in the car to drive two screw-propellers, right and left-handed, 3 ft. in diameter, with four blades each, occupying three-quarters of the area of the circumference, set at an angle of 60 degrees. A considerable time was spent in perfecting the motive power. Compressed air was tried and abandoned. Tappets, cams, and eccentrics were all tried, to work the slide valve, to obtain the best results. The piston rod of engine passed through both ends of the cylinder, and with long connecting rods worked direct on the crank of the propellers. From memorandum of experiments still preserved the following is a copy of one: June, 27th, 1845, water 50 ozs., spirit 10 ozs., lamp lit 8.45, gauge moves 8.46, engine started 8.48 (100 lb. pressure), engine stopped 8.57, worked 9 minutes, 2,288 revolutions, average 254 per minute. No priming, 40 ozs. water consumed, propulsion (thrust of propellers), 5 lbs. 4 1/2 ozs. at commencement, steady, 4 lbs. 1/2 oz., 57 revolutions to 1 oz. water, steam cut off one-third from beginning.

'The diameter of cylinder of engine was 1 1/2 inch, length of stroke 3 inches.

'In the meantime an engine was also made for the smaller model, and a wing action tried, but with poor results. The time was mostly devoted to the larger model, and in 1847 a tent was erected on Bala Down, about two miles from Chard, and the model taken up one night by the workmen. The experiments were not so favourable as was expected. The machine could not support itself for any distance, but, when launched off, gradually descended, although the power and surface should have been ample; indeed, according to latest calculations, the thrust should have carried more than three times the weight, for there was a thrust of 5 lbs. from the propellers, and a surface of over 70 square feet to sustain under 30 lbs., but necessary speed was lacking.'

Stringfellow himself explained the failure as follows:--

'There stood our aerial protegee in all her purity--too delicate, too fragile, too beautiful for this rough world; at least those were my ideas at the time, but little did I think how soon it was to be realised. I soon found, before I had time to introduce the spark, a drooping in the wings, a flagging in all the parts. In less than ten minutes the machine was saturated with wet from a deposit of dew, so that anything like a trial was impossible by night. I did not consider we could get the silk tight and rigid enough. Indeed, the framework altogether was too weak. The steam-engine was the best part. Our want of success was not for want of power or sustaining surface, but for want of proper adaptation of the means to the end of the various parts.'

Henson, who had spent a considerable amount of money in these experimental constructions, consoled himself for failure by venturing into matrimony; in 1849 he went to America, leaving Stringfellow to continue experimenting alone. From 1846 to 1848 Stringfellow worked on what is really an epoch-making item in the history of aeronautics--the first engine-driven aeroplane which actually flew. The machine in question had a 10 foot span, and was 2 ft. across in the widest part of the wing; the length of tail was 3 ft. 6 ins., and the span of tail in the widest part 22 ins., the total sustaining area being about 14 sq. ft. The motive power consisted of an engine with a cylinder of three-quarter inch diameter and a two-inch stroke; between this and the crank shaft was a bevelled gear giving three revolutions of the propellers to every stroke of the engine; the propellers, right and left screw, were four-bladed and 16 inches in diameter. The total weight of the model with engine was 8 lbs. Its successful flight is ascribed to the fact that Stringfellow curved the wings, giving them rigid front edges and flexible trailing edges, as suggested long before both by Da Vinci and Borelli, but never before put into practice.

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