NO. 4 



WIND TUNNEL EXPERIMENTS IN AERODYNAMICS 



6i 



It is convenient to calculate the forces and moments about moving 

 axes fixed relative to the wing. The axes are lettered OX, O Y , and 

 OZ. In figures 22 and 23, point we have located at the middle of 

 the leading edge of each wing. OX is the fore and aft, OY the trans- 

 verse, and OZ the normal axis of the wing. When the wing has zero 

 incidence and yaw, the position of the axes is shown in figure 22 by 



Fig. 23. 



0X2, OY2, and OZ^. Now suppose the wing to be turned about 

 OZ2 through a positive angle of yaw \p. Then the axes will be in the 

 position, 0X3, OY, and OZ,. Now if the wing is given an angle of 

 incidence of about OY, the axes will swing into the positions OX, 

 OY, OZ. 



In making the calculations it is easier first to refer the forces and 

 moments to a set of axes parallel to OX, OY, and OZ, which we have 



