NO. 3 (JANGLE'S MEMOES ON MECHANICAL FLIGHT 9 



surface of the rudder is subjected to the unpad of the air, the rear end is raised, 

 and horizontality again attained. In addition to this, Penaud appears to have 

 contemplated giving the rudder-stem a certain elasticity, and in this shape it is 

 perhaps as effective a control as art could devise with such simple means. 

 Of the flight of his little machine, thus directed, Penaud says: 



" If the screw be turned on itself 240 times and the whole left free in a hori- 

 zontal position, it will first drop; then, upon attaining its speed, rise and perform 

 a regular flight at 7 or 8 feet from the ground for a distance of about 40 metres, 

 requiring about 11 seconds for its performance. Some have flown 60 metres and 

 have remained in the air 13 seconds." The rudder controls the inclination to 

 ascend or descend, causing oscillations in the flight. Finally the apparatus de- 

 scends gently in an oblique line, remaining itself horizontal." 



The motive power is a twisted hank of fine rubber strips, which weighs 5 

 grammes out of a total of 16 grammes for the whole machine, whose ceuter of 

 gravity should be in advance of the center of surface CD, as will be demonstrated 

 in another place. This device attracted little notice, and I was unfamiliar with 

 it when I began my own first constructions at Allegheny, in 1887. 



My own earliest models employed a light wooden frame with two propellers, 

 which were each driven by a strand of twisted rubber. 6 In later forms, the rub- 

 ber was enclosed and the end strains taken up by the thinnest tin-plate tubes, 

 or better still, paper tubes strengthened by shellac. 



Little was known to me at that time as to the proper proportions between 

 wing surface, weight and power; and while I at first sought to infer the relation 

 between wing surface and weight from that of soaring birds, where it varies 

 from \ to 1 sq. ft. of wing surface to the pound, yet the ratio was successively 

 increased in the earlier models, until it became 4 sq. ft. to 1 pound. It may be 

 well to add, however, that the still later experiments with the steam-driven 

 models, in which the supporting surface was approximately 2 sq. ft. to the 

 pound, proved that the lack of ability of these early rubber-driven models to 

 properly sustain themselves even with 4 sq. ft. of wing surface to the pound, 

 was largely due to the fact that the wings themselves had not been stiff enough 

 to prevent their being warped by the air pressure generated by their forward 

 motion. 



During the years I presently describe, these tentative constructions were re- 



1 1 have never obtained so .good a result as this with any rubber motor. S. P. Langley. 



"One pound of twisted rubber appears, from my experiments, to be capable of momentarily 

 yielding nearly 600 foot-pounds of energy, but this effect is attained only by twisting it too far. It 

 will be safer to take at most 300 foot-pounds, and as the strain musl be taken up by a tube or frame 

 weighing at least as much as the rubber, we have approximately 0.0091 as the horse-power for one 

 minute, or 0.091 horse-power for six seconds as the maximum effect, in continuous work, of a pound 

 of twisted rubber strands. The longitudinal pull of the rubber is much greater, but it is difficult tn 

 employ it in this way for models, owing to the great relative weight of the tube or frame needed to 

 bear the bending strain. In either form, rubber is far more effective for the weight than any steel 

 spring (see later chapter on Available Motors). 



