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CHAPTER X. 



PROPELLER PERFORMANCE CURVES. 



General. The problem is to find a curve giving P T , the effective 

 thrust horse-power available for flight, plotted on a base of V, 

 the speed of the machine, on the assumption that the engine is 

 working at normal torque^ and another curve giving, on a base of 

 V, P R , the effective thrust horse-power available for flight on the 

 assumption that the engine is working at normal revolutions all 

 in standard density air. 



Further, we have to find what these two curves become when 

 the machine is at a given altitude. 



Definitions. 



V is the speed of flight in miles per hour in standard den- 

 sity air. 



V is the designed speed of the propeller in miles per hour, 

 that is to say, that when the machine is flying (and perhaps 

 climbing) at this speed with the throttle full open, the engine 

 will develop its normal revolutions and its normal B.H.P. in 

 .standard density air. 



P T and P R are the effective thrust horse-power available for 

 flight with the engine working at full throttle and normal revolu- 

 tions respectively in standard density air. 



H is the normal brake horse-power in standard density air. 



" - fr 



# is the normal rate of revolution of the propeller in revolu- 

 tions per minute. 



d is the diameter of the propeller in inches. 



a is the ratio of the air density at an altitude to standard 

 air density, and is plotted on page 104. 



V is the speed of flight in miles per hour at an altitude. 

 P T ' and P R ' are the values at an altitude of P T and P R . 



