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707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 9:44 am

why is it that there are more re-engined DC-8s than there are 707s? is boeing holding out the necessary certification and engine work from the public?
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 9:54 am

The military versions of the 707 have been re-engined. Boeing did not promote it to civil air as this was thought to have been detrimental to the 757 program. There was a dedicated program to re-engine the DC-8-63 series. Both DL and UA participated. This was in the early 80s. These plane were in passanger service until 1991, and have been in cargo service ever since. Also the DC-8 airframe is considerably beefier than the 707s which make re-engine programs more feasable as there is more life left of the plane.
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 10:20 am

The main reason you see many more DC-8s than 707s is because the USAF bought a huge chunk of available airframes for spare parts to use on their C-135/137 fleet. These are/were all parked at DMA, though most of the extant airframes have been scrapped recently. Engine pylons were salvaged for the -A to -E upgrade, and tailplanes were used -135 fleetwide.

One other reason is that the 707 with CFM-56 engines has much less ground clearance than the DC-8. People thought that this would make the 707 much more likely to slam a pod down on landing in the hands of a civilian pilot (unfair i know).
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 12:37 pm

The USAF (and the rest of the DoD) is by far the largest CFM customer. Each KC-135 has four of them (and there are almost 500 of these), plus there is the E-6, plus the C-40, T-43, and soon the MMA. That means that there are around 2,000 CFM56s in DoD service.
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 1:14 pm

The DC-8 was also more desirable as a freighter because it can hold 13, 14 or 18 ULDs based upon which model it was. The 707 can only hold 13 ULDs.
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 1:21 pm

There are programs out there to re-engine the 707 with JT8D-219 engines. I know it is quieter and more powerful than the JT3D-7 engines.
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 10:00 pm

I've heard there has been a proposal to re-engine the entire USAF E-3A Sentry fleet with the JT8D-219 engine, though I'm not sure if that's a good idea given that the -219's won't have much more extra engine thrust compared to the TF33's now being used.

I think in the end, the E-3A's will get CFM56 engine upgrades, though that depends on how far along the E-10 project based on the 767-400ER airframe is coming along.
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RE: 707 Vs. DC-8: Re-engined

Wed Jul 21, 2004 10:23 pm

DC-8s were re-engined in JT8D-200 engines, and many of these were owned by Airborne Express. I don't know if DHL kept them.

It would be interesting to see the JT8Ds on a 707...
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RE: 707 Vs. DC-8: Re-engined

Thu Jul 22, 2004 2:06 am


Could you post a picture of a DC-8 wth JT8-D 200s? I've seen the Airborne ones with JT-3Ds in quiet nacelles (after huhkitting) but the only 4 engine aircraft I've seen with JT-8D 200s is the single 707 that was converted a few years ago.
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RE: 707 Vs. DC-8: Re-engined

Thu Jul 22, 2004 2:14 am

DHL's DC-8 are -71's and -73's. I've never seen a JT8D-200 series on a DC-8. Only saw it on a 707. Airborne Express DC-8's are all -63F's with Stage III JT3D-7B's.
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RE: 707 Vs. DC-8: Re-engined

Thu Jul 22, 2004 2:14 am

A more controversial re-engine project would have been Boeing's proposal to fit 4 RB211-535E4 engines to the B-52 in a life extension program.

Buildup and support would presumably go to Rolls Royce USA (Allison)

I don't think any DC-8s got to be re-engined with the JT8D as the CFM offered better all-round performance and higher cargo weights. The Airborne ones were the -63 variant with the smoother nacelle, which could be where the confusion comes in. The -61 had nacelles similar to the Jet Trader series 50 and the 63 had the nacelles from the shorter -62.

The JT8D was offered as an option initially.

[Edited 2004-07-21 19:25:26]
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