58 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 62 



bility for wings swept back 30 degrees are therefore paid for by a 



considerable loss in effectiveness. 



The ratio ,,^ of 16. S for the 



normal wing and for No. II is reduced to 12.9 for No. IV. 



The center of pressure motion is shown by the curves of figure 20, 

 in which it appears that the motion is similar for all the wings tested. 



Fig. 20. 



The center of pressure motion gives rise to the same degree of longi- 

 tudinal instability. The center of pressure is referred to the forward 

 point of the middle longitudinal section of each wing, and it appears 

 that for a given angle of incidence the center of pressure is thrown to 

 the rear by about two-tenths of the chord for a sweep back of 10 

 degrees, and four-tenths of the chord for a sweep back of 20 degrees. 

 The center of gravity of an aeroplane will, therefore, have to be 

 placed farther to the rear if swept back wings are used. 



