ferpe
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RR Trent700 Nacelle Design

Thu Oct 04, 2012 7:59 am

Please help me understand why RR designs longer nacelles then GE and PW. It is evident on the A330 but also on other implementations. Here the 330 with in order RR T700, GE CF6 and PW4000:




The longer nacelle is not limited to RR 3-shaft engines, their influence is also evident in the IAE V2500 nacelle. What does one gain with a longer nacelle vs a shorter one?

[Edited 2012-10-04 01:00:48]
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Jetlagged
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RE: RR Trent700 Nacelle Design

Thu Oct 04, 2012 2:00 pm

Rolls Royce turbofan engines use a mixed core and fan exhaust design, hence the longer bypass cowling which is an integral part of the powerplant. Exhaust mixing provides better thrust, reduced fuel consumption and less noise compared to the non-mixed shorter cowled designs as used by PW and GE. The downside is increased weight and drag. RR three shaft engines tend to be shorter than comparable two shaft turbofans so the weight and drag penalty will be less than for a two shaft engine.
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tdscanuck
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RE: RR Trent700 Nacelle Design

Thu Oct 04, 2012 5:31 pm

Quoting ferpe (Thread starter):
Please help me understand why RR designs longer nacelles then GE and PW.

Jetlagged summed it up nicely. A couple of important points to elaborate:
-The nacelle isn't actually longer, it's just that the bypass duct is longer (so it covers up the inner exhaust cone that you can otherwise see on PW and GE nacelles).
-It's not universal...the Trent1000 and GEnX nacelles are very similar (and use the short bypass duct)
-RR is generally unique in usually doing the nacelle/engine as a unified package. The nacelle for PW and GE normally comes from somebody else (and is often designed by the OEM) independently of the engine.

Tom.
 
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bikerthai
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RE: RR Trent700 Nacelle Design

Thu Oct 04, 2012 6:36 pm

For the 777, didn't the Rolls have smaller fan diameter than the other two? That may skew the proportion a little to make them look longer also.

bt
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ferpe
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RE: RR Trent700 Nacelle Design

Thu Oct 04, 2012 8:07 pm

Thanks Jetlagged and Tom. Interesting that RR makes their own nacelles and thereby could optimize a little bit differently, I guess they do not make the T1000 nacelle?
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rmm
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RE: RR Trent700 Nacelle Design

Thu Oct 04, 2012 11:36 pm

GE thru CFMI used that design on the early A340's. The cfm56-5 on the 340 had a full length duct, similar to the RR design, yet that engine on the A320 didn't. Then to add to the mix, the v2500 on the 320 has a full length duct.
 
tdscanuck
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RE: RR Trent700 Nacelle Design

Fri Oct 05, 2012 1:08 am

Quoting ferpe (Reply 4):
Interesting that RR makes their own nacelles and thereby could optimize a little bit differently, I guess they do not make the T1000 nacelle?

I believe the Trent 1000 nacelle comes from Goodrich, same as the GEnX nacelle.

RR used to "own" more of the nacelle package than the other two, in general, including oddities like having the fire extinguisher bottles in the nacelle (the other guys usually have it in the strut or in the fuselage somewhere). In the particular case of the 787, the requirement for the ability to swap engines post-delivery made those kinds of design choices much more difficult and biased them towards a more common approach.

Tom.
 
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bikerthai
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RE: RR Trent700 Nacelle Design

Fri Oct 05, 2012 1:27 pm

Quoting ferpe (Reply 4):
Interesting that RR makes their own nacelles

If my memory serves me right, was the 777 RR nacelle designed and built by Boeing?

If this was the case then two of the reasons are the proprietary method in fabricating the perforated composite inner skins of the inlet and reverser duct, and the pitch graphite honeycomb core of the inner T/R duct wall. I was around when they did R&D for those technology. Saved a lot of weight over existing methods.

Perhaps that is why they kept the nacelles for the 787 also.

bt
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