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JT8D Vs. CFM-56 Vs. IAE V2500

Tue Jun 13, 2000 10:56 am

The MD-80 has been described as being fuel-efficient, yet it's engines have only a a 1.8 bypass ratio. The 737's CFM-56s (the ones used on the 737-300 through -500 (seem to have much higher bypass ratios). Are they more efficient? The MD-80's cross-section is more slender and it takes less fuel to propel it through the air. But is that enough?

I must admit that I'm a great fan of the IAE V2525 used on the MD-90. They're very quiet, efficient, and they look good. Can anyone tell me if the A320 is better powered by the CFM-56 or IAE 2500, and what would make airlines choose one or the other?

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RE: JT8D Vs. CFM-56 Vs. IAE V2500

Tue Jun 13, 2000 8:22 pm

Some chose the CFM56 because either they had experience with the engine on the 737 or they are a GE customer like US Airways for example. With the IAE V2500, they are probably a P&W or RR customer like United and British Airways.
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RE: JT8D Vs. CFM-56 Vs. IAE V2500

Tue Jun 13, 2000 11:25 pm

It's hard to judge why based on hindsight I guess. I don't think it's a black and white,right/wrong thing. That one engine may not be as "efficient" on paper doesn't make it completely inferior. The JT8 family predates all the high bypass engines by a large margin,and so by designing a "big block" version that is more powerful and quieter than the older "small blocks" (-7 thru 17) while maintaining some commonality it, filled a need in the early 80's. In any event I think it'd be quite a challenge mounting one of the CFM's on the stubwing of an MD80. When they were designing the MD80 in the late 70's the CFM was too far into the future to hang on a plane right then. IIRC from school on the CFM56, it's core engine is based on the GE F100 used in jet fighters,but the SNECMA alliance fan engine verion wasn't out till the MD80's were in the market. I don't kow anything about the V2500, but then again,don't forget the time frame. I'd just like to add that the JT8 is a damn good engine even if it's not state of the art today. (what IS forever?)
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RE: JT8D Vs. CFM-56 Vs. IAE V2500

Wed Jun 14, 2000 1:30 am

True, the CFM56 is more efficient than the JT8D but its also much newer and it generally is not offered in place of the JT8D. JT8D-217 powered MD-80s are not quite as efficient as CFM56 powered 737-400s, compared because of their identical seating capacities (around 140). The MD-80, despite having a more slender cross section is a heavier aircraft. An empty MD-82/83 weighs in the neigborhood of 87,000 lbs with later build models at around 84,000 lbs. The 737-400 weighs between 74-77,000 lbs empty. Fully laden a long range MD-83 weighs 160,000 lbs MTOW. The 737-400 at 142,500 is quite a bit lighter. That might where the difference in efficiency came in.

The IAE powerplants are very efficient, more so than the CFM but they too are newer than the CFM design. I just dont think there are as many out there compared to other comparable models. Fleet commonality plays a big role and adding a new engine to the mix is expensive when you could choose the JT8D (MD-80/90) or the CFM (Airbus A320). The 737 doesnt offer the CFM or IAE unit as an option anyway!
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RE: JT8D Vs. CFM-56 Vs. IAE V2500

Wed Jun 14, 2000 3:52 am

Just to compare the IAE and the CFM's, the IAE V2500 has a lower fuel burn than the CFM56, but from what I've heard that's the only thing it's got going for it, other than perhaps purchase price. Naturally some airlines will choose it for that reason, but just from what I've heard from mechanics the V2500 is less reliable, has shorter amount of time between overhauls, and is a pain to work on compared to the CFM56's. Both engines are compared for people working on A320 aircraft, working on both engine types. Whether you believe what they say or not, the claim from CFM is that the CFM56 is cheaper to operate overall when you consider its longer life and lower maintenance costs, but I guess that comes down to how long the aircraft stays in the fleet, and of course which manufacturers propaganda you listen to.

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