Re: Re-engining 747s

Date:         23 Dec 98 03:52:58 
Organization: Deja News - The Leader in Internet Discussion
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kls@ohare.Chicago.COM (Karl Swartz) wrote:
> >To my knowledge, this is the first time a 747 is re-engined; is this correct?
> >(ie not counting engine upgrades such as eg on Cathay's RB211-engined 747s.)
> There are a fair number of examples of re-engining, both minor upgrades
> (such as the CX 747s you mention or many early 747s which ended up with
> newer JT9D variants) or major ones (such as the DC-8-70 series with
> CFM-56 engines or the RR Tay upgrades for the 727).

There certainly are many examples of re-engining. But it's one thing to
re-engine with something substantially better (as with the CFM-powered
DC-8-70); it's another to swap one engine with an essentially equivalent one
(as in this case of the Atlas 747s).

> I can only think
> of three cases prior to the Atlas planes, however, where jetliners
> underwent a major re-enginging not for efficiency but simply for
> convenience:
>  * The sole 707-700 (built with CFM-56 engines) was converted to 707-320
>    spec, complete with old JT3D or JT4A engines.

Well, since you can't sell a non-certificated model (and even if it was
certificated, who would buy a one-off model?) this is more than just
convenience. Simply put: if Boeing wanted to sell this aircraft, they had no
choice but to swap the CFMs for JT3Ds.

>  * Airbus converted at least one A330 between RB.211 and PW4000 engines.
>    I can't remember which was first but it was a flight test aircraft for
>    both engine types.  Might have been an artifact of crashing one of the
>    PW4000-equipped flight test planes.

They also converted one of the original A310 prototypes from GE to PW engines
before selling it to Swissair, if memory serves.

Both these cases, and the 707-700 case, concern test aircraft, though.
There's probably a lot you need to do to these aircraft to bring them up to
delivery standard anyway, so changing engines may not be as big a deal as in
other cases.

The main issue is that re-engining involves more than changing the hardware
that's hanging off the pylon. A lot of wiring and engine controls need to be
changed too. This isn't the case with minor upgrades, so they can be done
easily enough, usually. If you're putting substantially better engines on,
then this extra cost may be worth bearing, as on the DC-8-70. In the case of
test aircraft, you're probably doing a lot of internal system changes anyway
(either to rip out systems needed only for flight testing, or to bring
existing systems up to production standard) so the incremental cost of also
changing engine systems isn't as large.

Stefano Pagiola
All opinions are my own.
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