In the above trials of the superposed wings, the conditions of the wind and of the aerodrome were certainly as favorable as could be expected. There was as much power being furnished by the engine as had been furnished in the previous flights with the “single-tier” wings, and the balancing of the aerodrome was exceedingly good. The superposed wings, unquestionably, had a fair trial and proved inferior to the “single-tier” ones, for they had a supporting surface of 2.75 square feet to the pound, whereas with the “single-tier” wings there was approximately 2 square feet to the pound. The decreased lifting power of the superposed wings seems to be another confirmation of the results of the Allegheny experiments with the “plane-dropper.”[40]
As more time had already been given to these tests than it seemed well to [p151] spend on them at that time, owing to the pressure of the work of construction for the large machine, it was deemed best to discontinue them for the time being, and as soon as time could be found for it, to construct a set of wings with superposed surfaces, using only two surfaces and making their distance apart at least equal to or greater than their width.
It will be remembered that the prime object in making these tests was to obtain data for use in the balancing of the large aerodrome and in constructing a launching apparatus for it. The chief deductions drawn from them were: First: That it would be best to construct the first set of wings for the large machine on the “single-tier” plan, and later to make a set of superposed ones, should further experiments with new designs develop a type of superposed surfaces which gave as good lifting power as the “single-tier” ones. Second: That the proportioning of the coefficient of elasticity of the Pénaud tail should be given as careful attention as the setting of the wings. Third: That the “underneath” launching apparatus was equally as good as the “overhead” one, and that both worked as well as could be desired; and, fourth, that while short periods of calm weather might be expected during some part of the day on a portion of the days of each month, yet the most favorable conditions were more apt to be met with between the first break of day and the actual rising of the sun, or from an hour preceding sunset until darkness actually came.
It will be noted that while considerable delay was experienced in making these tests, nearly all of it was due to the very delicate adjustments required in the power-generating apparatus of the aerodrome, but it should also be noted that when these adjustments were accurately made the models operated exceedingly well, and could be depended upon to give good flights of sufficient duration to permit a careful study of their action while in the air.
In the experiments of June 27 and July 7, above described, the aerodrome immediately after leaving the launching apparatus began to rise with its midrod pointed upward at an angle of about 15 degrees. From Data Sheet No. 6, which gives in detail the important data as to the settings of the wings, the elasticity of the Pénaud tail,[41] etc., we note that the tail had a negative angle of 712 degrees, and that the spring which held it at this angle was of such a stiffness that it required 1240 grammes placed at its center of figure to depress it to the horizontal. It will also be noticed that the position of the front and rear [p152] wings relative to the center of gravity of the machine was not the same as that which existed at the time of the very successful flights of 1896, as shown by Data Sheet No. 1 of No. 5, May 6, 1896. When the elasticity of the tail was adjusted before making this test it was thought that it was made the same as in the experiments of 1896, though accurate data as to the exact amount of this elasticity had, unfortunately, not been kept.
A slight change had also been made in the method employed of attaching the Pénaud tail to the machine. In 1896 the tail was attached to the machine by means of a flat piece of wood (hickory) which had been steamed and bent to the proper extent to cause the rudder to have a negative angle of about 5 degrees, but no accurate note was made of its angle or stiffness, so that in 1899 no data were available as to exactly what the angle had been or how stiff the spring was. Owing to the fact that wood not only warps and twists, but also that any piece which has been steamed and bent gradually loses a certain amount of its curvature, it was decided in 1898 to change this method of attaching the tail, the wooden spring being replaced by a coiled steel spring attached to an upper guy-post and connected to the tail by a bridle wire fastened to the center of figure of the tail.
After the experiment of July 7, 1899, a lower spring, consisting of small rubber bands, was connected by a wire to the lower part of the rudder and fastened to the guy-post, thereby more nearly reproducing the conditions obtained when using a wooden spring, which, of course, tends to return the rudder to its normal position when it is displaced in either direction. After attaching this lower spring to the rudder, the experiment of July 14 was made, and it was found that the aerodrome still flew with its midrod pointed upward at a very steep angle. It was, therefore, felt certain that the upper spring on the rudder was too stiff, and that it should not require so much as 1240 grammes to bring it to the horizontal. This spring was, therefore, replaced by a weaker one, and the angle of the rudder was also decreased until it had a negative angle of only 5 degrees and required only 200 grammes placed at its center of figure to bring it to the horizontal. From the description of the flight of July 19, it will be seen that these changes immediately corrected the tendency of the aerodrome to point its nose upward at such a sharp angle, and it will be later seen that after a further slight adjustment the flight of July 29 was made, in which the proper balancing was obtained and the aerodrome made a good horizontal flight.
After these preliminary tests with the “overhead” launching apparatus, it was dismounted and the “underneath” one substituted and the experiments of July 28, 29 and August 3 were made. Everything connected with this “underneath” launching apparatus worked perfectly from the start and four flights of the aerodromes were made using it.
PL. 37. EXPERIMENTAL FORMS OF SUPERPOSED SURFACES, 1898, 1899 (SEE ALSO PLATES 64 AND 65) [◊]