CHAPTER IX. 



WING CHARACTERISTICS. 



Definitions. The lift coefficient in non-dimensional units is 

 denoted by L and the drag coefficient by D ; the lift divided by 

 the drag or kjkv is denoted by L/D ; the value of L at the 

 stalling angle, i.e. the maximum value of L attainable, is denoted 

 by k imax \ kjk^ max \s> denoted by X; the centre of pressure co- 

 efficient is denoted by k c . 



Aspect ratio is the ratio of the overall span to the length of 

 the main chord of the wing : if the aspect ratio is different on 

 the top and bottom planes, the mean should be taken. Gap/ 

 chord is the ratio of the perpendicular distance between the two 

 chord planes to the length of the chord (or to the mean of the 

 top and bottom chords, if these differ). Stagger is the angle in 

 degrees between the line joining the top and bottom leading 

 edges and the normal to the chord. Wing tip shape is considered 

 as the ratio of the span of the rounded part of one tip to the 

 chord. Dimensions means the product of the chord (in inches) 

 of the model used for determining the characteristics of the wing 

 section to be employed and the speed (in feet per second) at 

 which the test was carried out. 



Tabular Method. The corrections on the model test values 

 of k^ max and L/D are most conveniently handled by means of a 

 table on the following lines * (see next page) : 



The left-hand column should be filled in as indicated : the 

 next five columns are then to be filled in by referring to the curves 

 on pages 88 to 97 : the curves are marked with numbers 

 corresponding to the A, column, the dotted curve in each case 

 corresponding to k vnax . Sufficient accuracy is obtained by re- 

 cording corrections to three decimal places (some of the curves 

 are plotted to scales which render closer reading possible, but 

 this has only been done to prevent the curves being too close 

 together to be seen clearly). 



* The device of dividing a table by horizontal lines after every third figure will 

 be found very useful and is recommended for general adoption in manuscript work : 

 it has the advantage of keeping the figures separate without obscuring the page with 

 a complexity of lines. 



