MACHINE PERFORMANCE CURVE 23 



Second Method. Assumptions. Line of flight horizontal. 

 Propeller thrust horizontal at all speeds of flight and passing 

 through the centre of head resistance. Slip stream neglected. 



Definitions. These are the same as in the First Method, but 

 in addition : 



/ is the horizontal distance in feet from the e.g. of the machine 

 to the c.p. of the tail plane.* 



/' is the horizontal distance in feet from the leading edge of 

 the equivalent chord to the c.p. of the tail plane. 



c is the chord of the wing in feet. 



k c has been defined in Chapter II. 



The equivalent chord is of course the chord of the equivalent 

 plane, which is an imaginary monoplane situated between the 

 top and bottom planes of the actual biplane, but -55 of the gap 

 from the lower plane : it has the property that for purposes of 

 moments it can be considered to replace the actual biplane. 

 Hence the line of action of L cuts the equivalent chord at a 

 distance ck c from the leading edge (see figure). 



We now have on our present assumptions a set of equations 

 very like those of the First Method, namely 



VT 



" 375 



(0 



* It is sufficiently accurate for our purpose to assume that the c.p. of the tail 

 plane is at the front tail plane spar. 



