I wanted to know how we knew auto provided 60% more seat miles when all seat in both vehicles are filled in the last part of 3

The Energy-State Approach to Airplane Performance 285 CDTotal=CDP+CDi+CDc=0.0202+0.00496+0.0010=0.02616DL=CDCL=0.026160.3337=12.76 Speed Mach of no. sound (a) Cruisedistance=cVDLlogWFWi=0.82(0.78)(686.9)12.76loge82,00097,000=(8350)(0.168)=1403statutemiles (b) T=D=CDToTqS=(0.02616)(268.18)(1000)=7015.6lb or T=D=L/DW=12.7689,500=7014.1lb (the difference is in the rounding of numbers) (c) Fuel flow (b/h)=Tc=7014.1(0.82)=5752lb/h Fuel flow (gal/h)=6.75752=858.4gal/h (d) Seat-miles / gal =858.41000.78(686.9)=62.42 seat - miles / gal (e) Auto has 5 seats 20 miles /gal=100 seat - miles /gal DC-9auto=62.42100=1.6 That is, the auto provides 60% more seat-miles/gal when all seats in both vehicles are filled. xample 15.2 A DC-9-30 with a capacity of 100 passengers is cruising at a Mach number of 0.78 at a pressure altitude of 30,000ft. Outside air temperature is 38F. The initial cruise weight was 97,000lb. According to the pilot's flight plan, he will start his descent at a weight of 82,000lb. The DC-9.30 has a CDP of 0.0202 , an e of 0.816 , a wing area of 1000ft2, a wing span of 93.6ft, and three lavatories. The compressibility drag coefficient CDC is 0.0010 . The JT8D-15 turbofan engines have an installed specific fuel consumption at cruise of 0.82lb/lbh. 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 6.7lb/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 20mi/gal. Solution: We are given hp=30,000ft,M=0.78, and T=38F=422R. Then speed of sound, a=RT=(1.4)(1718)(422)=1007.5ft/s=686.9mph qaverageweightCL=2pM2=21.4(629.7)(0.78)2=268.18lb/ft2=297,000+82,000=89,500lb=qSW=(268.18)(1000)89,500=0.3337 Since AR=Sb2=1000(93.6)2=8.76CDi=AReCL2=(8.76)(0.816)(0.3337)2=0.00496