NO. 3 LANGLEY MEMOIB ON MECHANICAL FLIGHT 1 .") 1 



spend on them al thai time, owing to the pressure of the work of construction 

 for (lie large machine, it was deemed besl to discontinue them for the time be 

 ing, 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 construct 

 ing a launching apparatus for it. The chief deductions drawn from them were: 

 First: That it would be best to construct the first set of w ings for the large ma 

 chine 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 sur 

 faces which gave as good lifting power as the " single-tier " ones. Second: 

 That the proportioning of the coefficient of elasticity of the Penaud tail should 

 be given as careful attention as the setting of the wings. Third: That the " un- 

 derneath " 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. 



Tt 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 exceed- 

 ingly 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 mid- 

 rod 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 Penaud tail, 3 etc., we note that the tail had a negative angle of 

 1\ degrees, and that the spring which held it at this angle was of such a stiff- 

 ness 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 



3 In fact the setting of the tail at a negative angle and Fastening it to the frame by an elastic 

 or spring connection was only begun in 1896, and while it proved to be the key to the solution of the 

 problem of automatic longitudinal stability, yet it was not at that time so recognized, although the 

 first real test of the aerodromes after the elastic connection and negative angle of the tail were 

 adopted resulted in the epoch-making flight of No. 5 on May 6. By comparing the angle of the 

 tail on No. 5 in Plate 27A, Part I, with the angle of the tail on No. (! in Plate 27B, Part I, it will be seen 

 that while the first had an angle of much less than 5 degrees, the latter had an angle of about 15 

 degrees. But the wooden springs changed so that it was not accurately known what the angle 

 really was at the time of either flight in 1890. 



