Although the repeated successful flights of model No. 5 under varying conditions of wind and power inspired the belief that the minor adjustments, as well as the general plan of the large aerodrome, were such as to give highly stable equilibrium, nevertheless, more direct corroboration of this opinion was desired, and it was largely for this reason that the quarter-size model was constructed. In it every detail of the larger machine which in any way affected its equilibrium was exactly reproduced to scale, and the greatest care was taken that the same relative positions of the center of pressure, the center of gravity and the line of thrust which it was proposed to employ for the large aerodrome should be used on the model in its flight of August 8, 1903, which is later described. The entire success of this flight, so far as the balancing was concerned, in spite of the fact that the engine worked erratically and that the launching speed was much less than it should have been, removed every doubt [p211] that the equilibrium of the large aerodrome would be satisfactory under normal conditions. The second problem encountered in connection with the balancing and control of the large aerodrome was that of providing an efficient means for maintaining the equilibrium under varying atmospheric conditions. Although much had been done toward the solution of this problem in the development of the models, the whole question was reopened and thoroughly reconsidered in designing the large aerodrome. The Pénaud tail, when made elastic or when more or less rigid, but attached to the frame through an elastic connection, and normally set at a negative angle, furnishes a means of automatically controlling the equilibrium, which is sufficiently sensitive and accurate to enable a machine to fly for a considerable distance, at least in moderately calm weather, as is evidenced by the various flights of the model aerodromes, where there was no human intelligence to control them. But owing to the principle of action of the Pénaud tail, the flight of an aerodrome controlled by it must of necessity be more or less undulatory in its course. Furthermore, the tests with the models had indicated that, while the Pénaud tail served remarkably well as a means of controlling the equilibrium of the machine, provided the balancing had been rather accurately determined, and, further, provided nothing happened to affect seriously the equilibrium of the machine, it was limited in its effectiveness by its narrow range of action. It was thought that a control mechanism which should be more sensitive and at the same time should act more powerfully to prevent the upsetting of the equilibrium when the machine was subjected to rather strong disturbing forces was desirable for any machine which was to transport a human being and, therefore, involved the risk of a fatal accident.