THE PLANE-UROPPER. 



37 



soai'ing speed. From Fig. 3 we find that the soai'ing velocities corresponding 

 to these angles are respectively 14 and 17.2 meters per second. 



Taking the vertical component of pressure as equal to the weight of the plane, 

 464 grammes, which relation obtains at soaring speed, the horizontal component 

 of pressure, or the resistance to advance, is given by the formula : 



R = 464 tan 9° = 73.3 grammes, for 9° ; 

 R = 464 tan 5° = 40.6 grammes, for 5°, 



a formula which is immediately derived from the fundamental principles of 

 mechanics and appears to involve no assumption whatever. The work done per 

 minute, ^ X F, is Q'2 kilogrammeters (450 foot-pounds) for 9°, and 43 kilogram- 

 meters (312 foot-pounds) for 5°. For the former case this is 0.0156 horse-power, 

 and for the latter case, approximately 0.0095 horse-power ; that is, less power is 



Fig. 4. 



A. 

 B. 





Reference. 



^ pair ofplane. f, 



, ^/irv apart 



1.0 



3^0 \U iSC ZO-0 



Times of falling 4 feet of single and double pairs of 15 x 4 inch planes. 

 Abscissce : Horizontal velocities of translation in meters per second. 

 Ordinates : Time of fall in seconds. 



required to maintain a horizontal velocity of 17 meters per second than of 14 ; a 

 conclusion which is in accordance with all the other observations and the general 

 fact deducible from them, that it costs less power in this case to maintain a high 

 speed than a low one — a conclusion, it need hardly be said, of the very highest 

 importance, and which will receive later independent confirmation. 



Of subordinate, but still of very great, interest is the fact that if a larger 

 plane have the supporting properties of this model, or if we use a system of 

 planes like the model, less than one-horse power is required both to support in 

 the air a plane or system of planes weighing 100 pounds, and at the same time 

 to propel it horizontally at a velocity of nearly 40 miles an hour. 



