AIR PERFORMANCE 37 



96W/ 



Gliding Angle. A comparison of curves (i) and (2) on page 

 157 will show that it is only at speeds close to the stalling speed 

 that the First Method and the Second Method give appreciably 

 different results. We will therefore content ourselves with the 

 simple assumptions of the First Method (suitably modified for 

 descending flight) in investigating the gliding angle. 



The forces acting on the machine are therefore only its total 

 weight W, the air lift L at right angles to the descending path 

 of steady flight, and the total air resistance of wings and body 

 T acting along the path of flight. 



Let 6 be the angle made by the flight path with the horizon : 

 then 6 is the gliding angle in still air. 



We will use similar notation to that of Chapter IV., and will 

 consider the machine to be gliding at an altitude, then by resolv- 

 ing horizontally we have 



L sin = T cos . . . . (i) 

 also, of course, we have 



L = a- x oo237 L S(i'467V') 2 . . . (3) 

 and L = \k^ max . (4) 



From equations (3) and (4) we have 



L= oo5i -X^ na ,SV' 2 . (L) 



Substituting for L from this equation in equation (2), we have 



T - - + ,o 5 r . . (T) 



From equations (i), (L), and (T) we have 



tan* = !=_L 4 



JL< 



R 



_ 

 L/D 



where a = ~Ji _ ...... (a) 



5 * * 



