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Why No Chevrons On The TrentXWB Or PW1000G?  
User currently offlineEA772LR From United States of America, joined Mar 2007, 2836 posts, RR: 10
Posted (4 years 7 months 2 days 6 hours ago) and read 10122 times:

I noticed (as anyone can) that the A350XWB lacks chevrons on its nacelle's like on the Trent 1000/GEnx-1B/GEnx-2B as well Pratt's PW1000G GTF doesn't either. Does anyone know why this is??






We often judge others by their actions, but ourselves by our intentions.
10 replies: All unread, jump to last
 
User currently offlineTrex8 From United States of America, joined Nov 2002, 4597 posts, RR: 14
Reply 1, posted (4 years 7 months 2 days 5 hours ago) and read 9973 times:
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they reduce noise but also increase fuel burn

User currently offlineLightsaber From United States of America, joined Jan 2005, 12784 posts, RR: 100
Reply 2, posted (4 years 7 months 2 days 4 hours ago) and read 9898 times:
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Quoting Trex8 (Reply 1):
they reduce noise but also increase fuel burn

 checkmark  A 1/5 to 1/4 percent fuel burn increase for about an 8 db noise reduction.

The GTF is such a high bypass engine that the noise reduction isn't worth the fuel burn. (The gases are already slow and diffused enough to mitigate noise.)

Please see slides 13 and 14. Basically, the GTF acheives 1 to 3 db lower noise than a competitor engine with the chevrons (its not stated in the presentation, but subtract 10 to 14 db from the 'current engines' for the new engines with Chevrons).
http://events.aaae.org/sites/080504/...crosoft%20PowerPoint%20-%20LEE.pdf

I would assume that RR believes the Trent XWB will be quiet enough sans the chevrons.

The NIMBY's will complain no matter what. So at some point it is better to optimize for fuel burn than noise.

Chevrons also are a weight penalty (stress concentrations instead of a nice 'barrel ring'). There is a oscillation (fatigue) risk with Chevrons too.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineEA772LR From United States of America, joined Mar 2007, 2836 posts, RR: 10
Reply 3, posted (4 years 7 months 2 days 4 hours ago) and read 9837 times:



Quoting Lightsaber (Reply 2):

Quoting Trex8 (Reply 1):
they reduce noise but also increase fuel burn

   A 1/5 to 1/4 percent fuel burn increase for about an 8 db noise reduction.

Thanks fellas for the info. I wonder if Boeing will return to a more conventional designed nacelle down the road. If Boeing was shooting for optimal efficiency, why did they use the chevrons?



We often judge others by their actions, but ourselves by our intentions.
User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3312 posts, RR: 40
Reply 4, posted (4 years 7 months 2 days 4 hours ago) and read 9799 times:

I thought I read somewhere that the engine cowlings are designed by Boeing and Airbus, and as Boeing holds the patient for the chevrons on certain engines, Airbus could not use them without penalty. Is this true or am I being daft?

By the way, the chevrons look fantastic on the 787 and 747-8, it's a shame no other large aircraft feature them. I believe they were tested on a GE-90 of an EVA air 777-300ER a while back.

Dave



Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
User currently offlineLightsaber From United States of America, joined Jan 2005, 12784 posts, RR: 100
Reply 5, posted (4 years 7 months 2 days 2 hours ago) and read 9648 times:
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Quoting EA772LR (Reply 3):
I wonder if Boeing will return to a more conventional designed nacelle down the road. If Boeing was shooting for optimal efficiency, why did they use the chevrons?

Boeing/GE/RR chose a small fuel efficiency penalty to make the plane far quieter. Part of the selling point of the 787 is less restricted night-operations. There are certain airports (e.g., night landings at LHR) where having a much quieter aircraft allows for more operations.

Quoting Legoguy (Reply 4):
I thought I read somewhere that the engine cowlings are designed by Boeing and Airbus, and as Boeing holds the patient for the chevrons on certain engines, Airbus could not use them without penalty. Is this true or am I being daft?

There are many patents on Chevrons. GE, Pratt, and RR all hold their own.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineAstuteman From United Kingdom, joined Jan 2005, 9944 posts, RR: 96
Reply 6, posted (4 years 7 months 2 days 1 hour ago) and read 9637 times:
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Quoting Lightsaber (Reply 5):
Boeing/GE/RR chose a small fuel efficiency penalty to make the plane far quieter. Part of the selling point of the 787 is less restricted night-operations

And yet it won't be any quieter than the A380. Airbus say they achieve the same result by other means...

Like many of these decisions, its about the trade-off that is chosen..

Rgds


User currently offlineLightsaber From United States of America, joined Jan 2005, 12784 posts, RR: 100
Reply 7, posted (4 years 7 months 2 days 1 hour ago) and read 9610 times:
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Quoting Astuteman (Reply 6):
And yet it won't be any quieter than the A380. Airbus say they achieve the same result by other means...

Yes, engine weight!  duck 

Seriously, as you noted Astuteman, there is a trade-off for each decision. Airbus with the A380 went with larger fans that cut the noise. This induced a weight penalty which hurts the A380 economics on shorter flights, but should be a pretty neutral change on longer flights (perhaps even a plus on ULH flights).

The Chevrons allow for low noise without as much weight. Thus, an airframe a little better optimized for shorter missions. The now defunct 787-3 rears its head.  Wink

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineAstuteman From United Kingdom, joined Jan 2005, 9944 posts, RR: 96
Reply 8, posted (4 years 7 months 2 days 1 hour ago) and read 9568 times:
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Quoting Lightsaber (Reply 7):
Airbus with the A380 went with larger fans that cut the noise.

 checkmark 
And IIRC deeper (as in thicker), more sound insulated nacelles

Quoting Lightsaber (Reply 7):
The Chevrons allow for low noise without as much weight

 checkmark 
Same result. Different trade-off.  Smile

Rgds


User currently offlineStitch From United States of America, joined Jul 2005, 30424 posts, RR: 84
Reply 9, posted (4 years 6 months 2 weeks 3 days 10 hours ago) and read 8457 times:
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Quoting Lightsaber (Reply 2):
The NIMBY's will complain no matter what. So at some point it is better to optimize for fuel burn than noise.

Based on the noise footprints for the 787 family and 747-8 Boeing have been posting, the number of NIMBY's complaining look to be significantly lower once those aircraft start to enter service.


User currently offlineAeroPiggot From United States of America, joined May 2005, 283 posts, RR: 0
Reply 10, posted (4 years 6 months 2 weeks 3 days 1 hour ago) and read 7383 times:

At the first flight of the 787 from Everett, I was standing by the runway, and that was the lowest engine noise I have ever heard from wide body twin. In fact I could not hear the 787 engines over the chase airplanes.


A scientist discovers that which exists, an engineer creates that which never was.
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