144 SOME AERONAUTICAL EXPERIMENTS. 



This time the velocity of the wind was 18 to 22 miles per lioiir. At 

 first we felt some doubt as to the safet}^ of attempting- free flight in so 

 strong" a wind, with a machine of over 300 square feet, and a practice 

 of less than live minutes spent in actual flight. But after several pre- 

 liminary experiments we decided to try a g'lide. The control of the 

 machine seemed so good that we then felt no apprehension in sailing 

 boldly forth. And thereafter Ave made glide after glide, sometiiues 

 following the ground closely and sometimes sailing high in the air. 

 Mr. Chanute had his camera with him and took pictures of some of 

 these glides, several of which are among those shown. 



We made glides on subsequent days, whenever the conditions were 

 favorable. The liighest wind thus experimented in was a little over 

 12 meters per second — nearly 27 miles per hour. 



It had been our intention when building the machine to do the larger 

 part of the experimenting in the following- manner: When the wind 

 ]>lew IT miles an houi' or more we would attach a rope to the machine 

 and let it rise as a kite with the operator upon it. When it sliould 

 reach a proper height the operator would cast off the rope and glide 

 down to the ground just as from the top of a hill. In this wa}" we 

 woidd l)e saved the trouble of carrying the machine up hill after each 

 glide, and could make at least ten glides in the time required for one 

 in the other way. But when we came to tr}" it we found that a wind 

 of IT miles, as measured by Richard's anemometer, instead of sus- 

 taining- the machine with its operator, a total weight of 240 pounds, 

 at an angle of incidence of 3 , in reality would not sustain the 

 machine alone — 1(»0 pounds — at this angle. Its lifting capacity seemed 

 scarcely one-third of the calculated amount. In order to make sure 

 that this Avas not due to the porosit}^ of the cloth, Ave constructed two 

 small experimental surfaces of equal size, one of Avhich Avas air-proofed 

 and the other left in its natural state; but Ave could detect no differ- 

 ence in their lifting- poAvers. For a time we were led to suspect that 

 the lift of curved surfaces little exceeded that of planes of the same 

 size, but further investigation and experiment led to the opinion that 

 (1) the anemometer used bv us overrecorded tlu* true velocity of the 

 Avind by nearly 15 per cent; (2) that the well-knoAvn Smeaton coeffi- 

 cient of 0.00.5 V" for the wind pressure at !M) is prolmbly too great Ija'' 

 at least 20 p(M- cent; (3) that LilicMithars estimate that the })ressure on 

 a curved surface having an angle of incidence of 3 e([uals 0.545 of the 

 pressure at 90 ' is too large, being nearly 50 per cent greater than very 

 recent experiments of our own with a s])(>cial ])ressure-testing- machine 

 indicate: (4) that the supei'position of the surfaces somcAvhat reduced 

 the lift per scjuare foot, as compai-ed with a single surface of ecpial 

 area. 



In gliding experiments, however, the amount of lift is of less 

 relative importance than the ratio of lift to drift, as this alone decides 

 the angle of gliding deseent. In a plane the pressure is alwaAs per- 



