106 EXPERIMENTS IN AERODYNAMICS. 



last experiment;! 1 result is not presented as a new contribution to knowledge, 

 since it had previously been obtained by experimenters in the early part of this 

 century ; but as their results appear not to have met with the general attention or 

 accej^tance they deserve, it is not superfluous either to produce this independent 

 experimental evidence or to urge its importance. 



The experiments with the Plane- Dropper introduce matter believed to be 

 novel as well as important. They show (1) that the time of falling of a hori- 

 zontal plane is greater when moving horizontally than when at rest, and (2) that 

 this time of falling most notably increases with the velocity of lateral translation ; 



(3) experiments with different horizontal planes show that this increase in the time 

 of falling is greater for those planes whose extension from front to back is small 

 compared with their length measured perpendicular to the line of advance , 



(4) the horizontal velocities are determined at which variously shaped inclined 

 planes set at varying angles can soar — that is, just sustain their own weight in 

 the air under such circumstances — and these data affbrd the numerical basis 

 for the important proposition that the power required to maintain the horizontal 

 motion of an inclined aeroplane is less for high speeds than for low ones ; (5) by 

 experiments with double planes, one above the other, it is shown that planes of 

 the advantageous shape mentioned above, do not interfere with each other at 

 specified speeds, if so placed at an interval not less than their length from front 

 to back ; and it is pointed out that an extension of this method enables us to 

 determine the extent to which any underlying air stratum is disturbed during 

 the plane's passage. 



Chapter VI contains further data, which confirm the impoi'tant conclusions 

 derived from the experiments with the Plane- Dropper^ already cited, and some 

 results on the pressures on inclined planes having different " aspects " with refer- 

 ence to the direction of motion are also presented, which are believed to be new 

 and of importance. Fui'ther chapters present experiments with a special instru- 

 ment called the Di/namometer- Chronograph and with other apparatus, which 

 give data regarding aerial propellers, a series of experiments on the center of 

 pressure of moving planes, and another series upon the pressure on a normal 

 plane. 



The conclusions as to the weights which can be transported in horizontal 

 flight have included the experimental demonstration that the air friction is 

 negligible within the limits of experiment. It has not been thought necessary 

 to present any evidence that an engine or other adjunct which might be applied 

 to give these planes motion, need itself oppose no other than frictional resist- 

 ance, i'f enclosed in a stream-line form, since the fact that such forms oppose 

 no other resistance whatever to fluid motion, has been abundantly demonstrated 

 by Froude, Rankine, and others. 



