NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 211 



that the equilibrium of the large aerodrome would be satisfactory under normal 

 conditions. 



The second problem encountered in connection with the balancing and cor 

 trol of the large aerodrome was that of providing an efficienl automatic means 

 for maintaining the equilibrium under varying atmospheric conditions. Al- 

 though much had been done toward the solution of this problem in the devel 

 opment of the models, the whole question was reopened and thoroughly recon- 

 sidered in designing the large aerodrome. The Penaud tail, when made elas- 

 tic 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 auto- 

 matically 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 prin 

 ciple of action of the Penaud 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 Penaud tail served remark- 

 ably well as a means of controlling the equilibrium of the machine, provided the 

 balancing had been rather accurately determined, and, further, provided noth- 

 ing 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 con- 

 trol 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. 



In the earlier period of the work and before the correct application of the 

 Penaud tail to the model aerodromes had been found, Mr. Langley had planned 

 a large number of different forms of automatic control for preserving the equi- 

 librium of the machines. The more frequently recurring of these were devices 

 for changing the angle of the wings or tail, and others for shifting the wings 

 or tail bodily so as to shift the position of the center of pressure with respect 

 to the center of gravity, the motive power for operating the devices being in 

 some cases that derived from a gyroscope or a pendulum, and in others small 

 electric motor apparatus controlled by a pendulum or a gyroscope. Most of 

 these, however, never reached the stage of development where thej were act- 

 ually tried on the machines in flight, as the tests of some of them in the shop 

 showed that they were unreliable, while others were abandoned either when 

 partly built or when only the drawings for them had been made. Anion- the 

 better-preserved models of devices for this purpose which were in existence 

 when the writer became associated with the work are those shown in Plate 68, 



