NO. 5 STABILITY OF AEROPLANES HUNSAKER AND OTHERS 



I I 



13, p. 81) were applied to the l./D curve for our model to obtain an 

 approximate curve of L/D to apply to the full-size wing. As a 

 monoplane surface, we get a maximum value of L/D of about 20. 

 The particular design is a biplane of aspect ratio 7. Well-known 

 corrections for biplane interference loss and aspect ratio gain were 

 applied to get a corrected curve for use in the design. 





Fig. 3.- — Wing section dimensions and resultant force vectors. 



The center of pressure for this wing is shown by figure 3, as well 

 as the contour of the section. Center of pressure is defined as the 

 intersection of the resultant force on the wing (represented as a 

 vector) with the plane of the chord. It is seen that the wing section 

 is unstable longitudinally at small angles. That is, if the wing heads 

 down so that the angle of attack becomes —3°, the moment of the 

 resultant force tends to turn it down still farther. 



Applied to the aeroplane, it is necessary to balance and correct this 

 tendency to dive by horizontal tail surfaces of proper size and 

 attitude. 



