136 AEROPLANE PERFORMANCE CALCULATIONS 



Let W be the total weight of the machine at the commence- 

 ment of the flight (that is the value of W used in finding the 

 machine performance curve) and let W be the weight of the 

 machine when she has flown till her tanks are dry. 



/ = -1 6 1 for stationary, and -262 for rotary engines. 



A is the full consumption of the engine in pounds per hour 

 (not pounds per B.H.P. hour) in standard density air. 



W = W fl + 







Then the cruising range in miles is 



but to secure the full mileage, if W is the weight of the machine 

 at any time during the trip, the machine must be flown at the 

 speed in miles per hour, of 



/W 7 ' 



v;J^-. 



Against a Head Wind of v Miles Per Hour. First determine 

 the altitude, either from practical considerations or, if these do 

 not prevent it, by the preceding method for finding the best 

 cruising altitude against the given wind. 



Now find V ', V T ', and V R ' for this altitude by a similar pro- 

 cess to that used for the calm. 



Then a, w, and W Q have the same values as above. 



Let x be the air miles to dry tanks, and / the time in hours 

 to dry tanks, then 



"^ " i ' 



log " L 



the angle being in degrees. An ordinary table of tangents can 

 be used to hunt up the angle in. 



