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Joined: Sat Dec 25, 1999 4:41 pm

Comparing Fuel Efficiency Of JT3D-3/7's & JT8D-9's

Thu Oct 12, 2000 6:44 am

Does anyone know if the JT3D-3 & JT3D-7 bypass engines that power first-generation DC-8's are comparable in fuel economy to the JT8D-9's that power aircraft like the 727-200 and the DC-9-30/50 series? This is something that I've wondered about for years and years. I realize that the JT3D-3's & JT3D-7's produce more lbs of thrust than JT8D-9's, so it's expectable that their overall fuel burn will be higher than the JT8D-9's, but is the ratio of fuel burn to thrust produced much different for these two engine types? When I consider two aircraft like the 727-200 and the DC-8-50, whose passenger capacities are about the same, it would appear on the surface that the DC-8-50 is less fuel efficient on a per passenger basis, but then I realize that despite having one extra engine, the DC-8-50 also has a considerably longer range than the 727-200 and so despite needing more fuel, it can take that same number of passengers a lot further. I'd welcome any feedback. Thanks in advance.
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RE: Comparing Fuel Efficiency Of JT3D-3/7's & JT8D-9's

Fri Oct 13, 2000 6:10 am

Jane's used to give cruise SFC's for some engines. For the JT8D-1 they showed 0.785 lb of fuel per hour, per pound of thrust, at max cruise at Mach 0.8 at 35,000 ft. Higher-rated JT8D's had steadily higher SFC's, reaching 0.825 for the -17. Jane's doesn't give cruise SFC for the JT3D, but various magazine articles indicated that it was little if any more than 0.825. Supposedly even the JT3C, JT4A and early Conways were in the 0.90-0.92 range. On the other hand, Jane's says the CFM56-5 on the A320 does 0.596.
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Joined: Tue Sep 19, 2000 12:53 pm

RE: Comparing Fuel Efficiency Of JT3D-3/7's & JT8D-9's

Sat Oct 14, 2000 6:30 am

At T/O rating, the JT3D-3B 18,000lbs st
The SFC is .535. I could not find cruise rating for SFC.

The T/O rating for the JT8D-15 is 15,500lbs. st, SFC is .630, cruise rating .811

The T/O rating for the JT8D-219 is 21,000lbs st ,SFC is .510, cruise rating is .737SFC

I know that the JT3D has a larger fan & higher bypass ratio than any JT8D version including the -200 series. But the -200 is a little more fuel efficient (and quieter).
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Joined: Tue Sep 19, 2000 12:53 pm

RE: Comparing Fuel Efficiency Of JT3D-3/7's & JT8D-9's

Sat Oct 14, 2000 6:38 am

I did not post info for the JT8D-9, the one that happy-flier spoke about.

The SFC at T/O is .595 and cruise is .807

The JT8D-9A is slightly more fuel efficient than -9.


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