Re: A330-300HGW & new gear

Date:         28 Jul 97 01:13:27 
From:         kls@ohare.Chicago.NOSPAM.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>There is discussion about a "new" engine for the A330HGW

>Question:
>	Could Airbus not install/use the same engines used on the 777 ?

Possibly, if it has the desired performance characteristics ... and it
fits.

>How much relationship is there between an engine and a plane's design
>and between an engine and a wing ? Is it just a question of fitting an
>engine that has the right thrust, or is there a lot more involved ?

There are the rather substantial matters of weight and size.  Consider
the PW4060/PW4062 used on the 767, the PW4168 used on the current A330,
and the PW4084 used on the 777:

   Model   Thrust  Diameter  Length  Weight
   PW4060  60,000     97.2    153.6   9,400
   PW4168  68,000    100      163.1  14,350
   PW4084  84,000    112      191.7  13,700

The PW4062 is probably the same size and weight as the PW4060.  The
PW4168 is somewhat larger and much heavier for a modest increase in
thrust.  The larger size/weight is the result of a larger fan, which
most likely gives much better fuel burn and more growth room.  The
even bigger engine on the 777 has a much bigger fan yet, and more
importantly, has lots of growth room without a significant change in
engine.

In the case of the A330HGW, the big question is whether or not the
much larger PW4084 would fit.  Look at the 737-300 compared to the
earlier 737-100/200 to see how much engineering grief can be caused
by retrofitting a larger engine.  Besides diameter, there's also the
question of length -- probably not so bad as it was for the center
engine of an L-1011, but at the very least it could introduce new
airflow interactions with the wing that would cause the aerodynamic
folks some grief.

Fitting the 777 engines might also be overkill.  If Airbus doesn't
need as much thrust as the larger engines offer, the added fuel burn
and the additional drag of the larger fronter area (from the bigger
fan) isn't going to do any favors for the A330HGW.

Fortunately, weight doesn't appear to be an issue in this case, since
the larger engine is a bit lighter.  But in many cases that's not true.
The original PW4000 includes engines from 52,000 lbs thrust up to the
62,000 lbs thrust PW4062/PW4162.  The 767 and MD-11 already use the
highest thrust engines in this sub-family, so any significant further
growth would require the bigger fan -- and consequent increase in
weight.  That might not be a viable upgrade.

Speaking of the MD-11, an added concern in some cases is greater air
flow.  The original DC-10 was designed with the air flow of the GE CF6
engine in mind.  The JT9D applied to the DC-10-40, and the higher-
thrust engines applied to the MD-11, require greater air flow than the
GE engines.  This is no problem for engines mounted in nacelles on the
wings (or sides of the fuselage), but the "banjo frames" which support
the vertical tail of the DC-10/MD-11 constrain the size of the center
engine's intake duct.  MD worked around this by using a bell-shaped
flare at the front of the duct on the DC-10-40 and MD-11.  This isn't
quite as efficient as a properly sized duct all the way to the engine,
but the penalty is apparently not overly burdensome.  (The same sort
of problem has required some creativity in 727 re-engining programs.)

--
Karl Swartz	|Home	kls@chicago.com
		|Work	kls@netapp.com
		|WWW	http://www.chicago.com/~kls/
Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills