74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 62 



IX. EXPERIMENTS ON A DIHEDRAL ANGLE WING 

 By J. C. HUNSAKER and D. W. DOUGLAS 



Following up experiments by Rossell and Brand showing the effect 

 on the lateral stability of sweeping back the wings of an aeroplane, 

 additional tests have now been made to determine whether the 

 righting moment given by the above procedure cannot be better 

 obtained by another method. To this end, a brass model i8 inches by 

 3 inches having curvature, known as R. A. F. 6,^ was made identical 

 in every way with the straight wing tested by Rossell and Brand, 

 except that each half of the wing was inclined upwards and outwards 

 2| degrees from the horizontal. This gave a dihedral angle upward 

 of 1/5 degrees. The use of this amount of angle has come into 

 general practice in aeroplane design. 



The wing was mounted horizontally on the balance and forces 

 and moments were measured for angles of yaw of o, 5, 10, 15, 20, 25, 

 and 30 degrees to right and left and at angles of incidence of 2, 4, 6, 

 and 9 degrees. The velocity of the wind was kept constant at 

 30 M. P. H. standard air. The method of manipulating the balance 

 to make the necessary measurements is described fully in Report 68, 

 Technical Report of the Advisory Committee for Aeronautics, 1912- 

 13 (London). The calculations, from the measured forces and 

 moments, to obtain the final results, were made as is outlined in the 

 preceding report on Swept Back Wings, by Rossell and Brand 

 (page 61). 



The axes along and about which the calculated forces and moments 

 act are as follows : 



OX — longitudinal axis coincident with chord at middle section. 



OY — transverse axis of wing, perpendicular to OX. 



OZ — normal axis of wing, perpendicular to OX and OY. 



The origin O is the intersection of the axis OX with the leading 

 edge of the wing. 



The forces are : 



X — acting along OX, positive when in direction of wind. 



Y — acting along OY, positive when tending to increase side 

 slipping to left. 



Z — acting along OZ, positive when acting upwards. 



The moments are : 



L — acting about OX, rolling moment, positive when wing tends to 

 take proper bank for turn to right. 



^Technical Report of the Advisory Committee for Aeronautics, London, 

 1912-13- 



