The Energy-State Approach to Airplane Performance CD Total L CL D Co = (a) Cruise distance T= D Cop + CD + ACDC 0.3337 0.02616 = (b) T = D = CD TOT S or L/D (c) Fuel flow (lb/h): Fuel flow (gal/h) Popes P = Mach of no. sound (0.78) (686.9) 0.82 c D (8350) (0.168) 1403 statute miles Tc 12.76 log 89,500 12.76 = WI WF - - = 0.0202 +0.00496 +0.0010 (0.02616) (268.18) (1000) = 7015.6 lb (d) Seat-miles/gal 858.4 (e) Auto has 5 seats x 20 miles/gal 7014.1 lb 7014.1(0.82) 5752 6.7 0.78(686.9) Speed 858.4 gal/h 12.76 loge 97,000 82,000 (the difference is in the rounding of numbers) 5752 lb/h 62.42 seat-miles/gal 100 seat-miles/gal 1.6 0.02616 auto 100 DC-9 62.42 That is, the auto provides 60% more seat-miles/gal when all seats in both vehicles are filled. A DC-9-30 with a capacity of 100 passengers is cruising at a Mach number of 0.78 at a pressure altitude of 30,000 ft. Outside air temperature is -38F. The initial cruise weight was 97,000 lb. According to the pilot's flight plan, he will start his descent at a weight of 82,000 lb. The DC-9-30 has a CDp of 0.0202, an e of 0.816, a wing area of 1000 ft, a wing span of 93.6 ft, and three lavatories. The compressibility drag coefficient ACDC is 0.0010. The JT8D-15 turbofan engines have an installed specific fuel consumption at cruise of 0.82 lb/lb-h. Determine: (a) Distance covered at cruise altitude (assume that conditions at average weight can be considered as the average for the flight). (b) Required engine thrust (total for two engines) at the average cruise weight. (c) Fuel flow in gallons per hour (kerosene weighs 6.7 lb/gal). (d) Seat-miles produced per gallon. (e) Compare the DC-9 seat-miles/gallon with a five-passenger automobile having a fuel consumption of 20 mi/gal.