172 AEROPLANE PERFORMANCE CALCULATIONS 



Example (8). Rate of Climb (Third Approximation}. Con- 

 sidering again the same machine as before 



S' = 85 (for the 135 inch propeller). 

 k imax = '590. 



d = 135- I37 - 5 * 8 , 5 X ' 59 = 378-2 



W = 5700. 

 RI= 135. 0- 7 ' 2 ' 35 = -0533. 



Now see table on next page. 



The curve of P x on V 1 as a base is plotted on page 170. 



Applying the method of the first approximation we find that 

 the maximum value of P p - P x occurs at a speed of 70 miles 

 per hour. 



.' Cma* = 33>QQQ 24S " I23 = 707 feet per minute. 

 5700 



Also this maximum rate of climb occurs at a speed of 70 

 miles per hour. 



Example (9). Times to Altitudes when the Curve of Rate 

 of Climb on a Base of Altitude is not Approximately a Straight 

 Line. 



Suppose we have the following data : 



C = 500 at standard altitude (i.e. at 800 feet). 



C = 385, 193, and 50, at 4000, 8000, and 10,000 feet 

 respectively. 



Then we plot and on an altitude base, and to get the 



v_/ \^ 



time to, say, 7000 feet, we take the area under the curve from 

 o to 7000 feet 



This area equals 18*4 in a unit which is the product of one 



foot of altitude and , i.e. the unit is 



i foot per minute climb 



minutes, 



.*. the time to 7000 feet is 18-4 minutes. 



Example (10). Times to Altitudes when the Curve of Rate of 

 Climb is Approximately Straight. 



Suppose we have the following data : 



C = 500 at 800 feet. 



C' = 370, 193, and 100 respectively at 4000, 8000, and 

 10,000 feet. 



