128 



L. HAH GRAVE. 



by the face of the following wave, which again enables it to resume 

 its velocity. 



Observe that the wave I instance in this example, is one of the 

 low round topped sort that prevail in calm weather. If we were 

 to base our calculations on a wave with a sharp crest approaching 

 to the breaking dimensions, our plane would be travelling on its 

 course through air having a velocity of uplift of 30 instead of 

 4*3 feet per second, if the wave slope were 45°; and would need 

 loading approximately to f^- x l'l = 76 lbs. per square foot to keep 

 it down to its original mean height, and could be made of seven 

 gauge wrought iron. 



If we figure out the result with 2° angle of incidence, and a 

 horizontal velocity of 65'6 feet per second, we find that the 1*1 K>. 

 plane will be supported where the wave face is only 4J° slope, 

 giving a velocity of uplift of 2*289 feet per second, and will make 

 a course 62° 40' to the right or left of that of the wave. Couple 

 this with the fact that the head resistance of a sailing bird's form 

 and the delicate arch of its wings are the survivals of untold 

 numbers of cruder types, and no surprise should be felt at any 

 intricate tactics pursued when further aided by the power derived 

 from the wind and roughened sea. 



This is the solution of the problem of a sailing bird's progression 

 totally denuded of complications. It becomes a giant's task to 

 compute the result when the effect of cross seas, wind at all angles 

 and ever varying force, arched surfaces, head resistance, ratio of 

 weight to area, and the intelligence of the guiding power crop up. 

 These questions all combined, have been considered in the evolu- 

 tion of a sailing bird and must be reckoned with by the designer 

 of a wave driven flying machine. I am not aware that anyone has 

 attempted to show that sailing flight by wave-power alone is a 

 practicable art, but even if some one else has done so, an observa- 

 tion from an independent source confirming old work cannot fail 

 to be of interest. 



