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How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 5:47 pm
by tsugambler
I've seen many older planes (such as DC-8s and 727s) re-engined to extend their service lives or increase their capabilities. How involved is the process of re-engining? I mean, it can't just be bolting a new engine on, can it? You would have to think about pylon design, and weight and balance, and aerodynamics, etc., right? Or is it simply taking an engine and installing it on a pre-existing aircraft?

RE: How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 5:58 pm
by etherealsky
I suppose it kind of depends on whether you're asking about the development of a re-engined modification for an aircraft type (would it be an STC?), or about the process of installing a new engine on an individual airframe.

If the former... I don't know about the engineering side of it, but I do know that the certification process alone is very comprehensive and expensive. In fact, I wouldn't be surprised if a certification effort required more of a company's resources than the design of the thing itself.

RE: How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 6:00 pm
by roseflyer
Re-engines require all new performance charts and requirements. Structure needs to be modified to support the new engine. It could be a simple pylon change or far more extensive if the airframe cannot support the additional weight of the engine without structural enhancements. All the systems need to change with the new engine gear box, and of course the fuel system will change.

RE: How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 6:20 pm
by tsugambler
I guess the primary example I have in mind is the DC-8... quite a few of them were modified from 61, 62, and 63s to 71, 72, and 73s with the CFM-56 engine. With the above considerations, I would have thought such an upgrade to be prohibitively expensive, but apparently not.

RE: How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 8:57 pm
by 411A
Quoting tsugambler (Reply 3):
I would have thought such an upgrade to be prohibitively expensive, but apparently not.

It was worthwhile primarily because of two considerations...
The DC-8 is an extremely robust design, in fact...the initial design service life of the airframe was 100,000 hours, from the get go.
(I know because my dad was involved with the early design)
And, the potential fuel savings AND performance enhancements using the CFM56 engine were outstanding.

Re-engined 707?
Except for a prototype, not done, because the specific 707 design did not lend itself to re-engining...with the CFM56. and be economical, at the same time.

Note 1.
Many of the later models of the DC-8 contained quite a lot of titanium, which is very light in weight, very strong, and lends itself to a proven robust aircraft design.
The only other aircraft design that contained more titanium, was...the L1011.
The latter, second to none in fuselage strength and robustness.
IE, manufactured very well in Palmdale.

Doubt?
Ask 474218...he positively knows, as he is (was)...a Lockheed guy.

Note 2:
The Flying Tiger Line operated re-engined DC-8's from HKG to HNL.
Departure from HKG at 357,000 pounds was possible, climbing to FL330...(FL370 after two hours) because of the added thrust thrust of the CFM56, and enabled nearly full payload ops, versus...older DC-8's having to land at PGUM, for enroute refueling.
A win-win scenario.

[Edited 2010-12-08 13:18:07]

RE: How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 10:09 pm
by tsugambler
Quoting 411A (Reply 4):

Wow, thanks for the detailed response! I can see how the business case for re-engining the DC-8 would really measure up.

RE: How Involved Is Re-engining A Plane?

Posted: Wed Dec 08, 2010 11:02 pm
by SEPilot
Quoting 411A (Reply 4):
Re-engined 707?
Except for a prototype, not done, because the specific 707 design did not lend itself to re-engining...with the CFM56. and be economical, at the same time.

Actually, the 707 was re-engined with the CFM56, but only military versions (as well as the KC-135, which is a different plane.) They did not do it commercially because the 757 and 767 were already in development by the time the CFM56 was ready, and few customers were interested in re-engining old 707's. Granted, the 707's were a less attractive candidate, being less rugged and also smaller than the Super 60 DC-8's.

RE: How Involved Is Re-engining A Plane?

Posted: Thu Dec 09, 2010 2:10 am
by KELPkid
Quoting SEPilot (Reply 6):
Actually, the 707 was re-engined with the CFM56, but only military versions (as well as the KC-135, which is a different plane.) They did not do it commercially because the 757 and 767 were already in development by the time the CFM56 was ready, and few customers were interested in re-engining old 707's. Granted, the 707's were a less attractive candidate, being less rugged and also smaller than the Super 60 DC-8's.

Don't forget, too, that the USAF was preparing for the eventual shutdown of the 707/717(military) line, and AMARC bought up almost all available civilian 707 airframes in the 1980's and flew them to the boneyard at Davis Monthan Air Force base, to be used as spare parts for the KC-135 and E-3 fleets. Selling used 707's to the Air Force turned out to be a lucrative business for many airlines   I'm sure that were it not for this development, we would have seen civilian 707 CFM56 engine swaps as well. Boeing even offered for sale new build 707-320's with CFM power, but there were no takers on that   That was probably the 757/767's doing...