E IMPACT OF JETS 379 



Iso, for tangential incidence, the direction of the vane at incidence 

 it be parallel to the direction of the jet relative to the vane, and must 

 therefore make an angle (3 with the direction of motion of the vane 

 where ft is obtained from the relationship (triangle a b c). 



v 



bin ft = . sin a. 



The initial velocity of jet in the direction of motion of vane = v cos a 

 final ,, ,, . 



= u - -r r cos (180 P) 

 = u + v r cos (0 + p) 



:. Change of momentum per sec.l WQ f ) 



= - } v cos a u v r cos (9 4- B) - 

 in direction of motion of vane ) g ' \ 



.'. Press on vane = | v cos a u v r cos (9 + ft) \ Ibs. 



AET. 109. GEAPHICAL CONSTRUCTION TO DETERMINE THE PRESSURE 



EXERTED ON A VANE (Fig. 170). 

 (1) Impact on a Fixed Vane. 



Let the vector BA represent the initial velocity of the jet in feet per 

 second. 



FIG. 170. 



Let the vector BC represent its final velocity on leaving the vane. 



Then AC '-represents the change of velocity, and therefore 

 gives a measure of the resultant pressure on the 

 vane, for if W Q Ibs. of water strike the vane per 

 second, the change of momentum in the direction 

 A C per second = WQ.AC-Z-g. 



