EA772LR From United States of America, joined Mar 2007, 2836 posts, RR: 11 Posted (2 years 5 months 1 week 4 days 3 hours ago) and read 6814 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.
Trex8 From United States of America, joined Nov 2002, 3722 posts, RR: 15 Reply 1, posted (2 years 5 months 1 week 4 days 2 hours ago) and read 6665 times:
Lightsaber From United States of America, joined Jan 2005, 8534 posts, RR: 100 Reply 2, posted (2 years 5 months 1 week 4 days 2 hours ago) and read 6590 times:
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.
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.
EA772LR From United States of America, joined Mar 2007, 2836 posts, RR: 11 Reply 3, posted (2 years 5 months 1 week 4 days 1 hour ago) and read 6529 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.
Legoguy From Ireland, joined Jun 2006, 3288 posts, RR: 50 Reply 4, posted (2 years 5 months 1 week 4 days 1 hour ago) and read 6491 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'?
Lightsaber From United States of America, joined Jan 2005, 8534 posts, RR: 100 Reply 5, posted (2 years 5 months 1 week 3 days 23 hours ago) and read 6340 times:
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.
Astuteman From United Kingdom, joined Jan 2005, 8610 posts, RR: 96 Reply 6, posted (2 years 5 months 1 week 3 days 23 hours ago) and read 6329 times:
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..
Lightsaber From United States of America, joined Jan 2005, 8534 posts, RR: 100 Reply 7, posted (2 years 5 months 1 week 3 days 22 hours ago) and read 6302 times:
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!
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.
Stitch From United States of America, joined Jul 2005, 23614 posts, RR: 79 Reply 9, posted (2 years 4 months 3 weeks 5 days 7 hours ago) and read 5149 times:
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.
AeroPiggot From United States of America, joined May 2005, 278 posts, RR: 0 Reply 10, posted (2 years 4 months 3 weeks 4 days 22 hours ago) and read 4075 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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From United States of America, joined Mar 2007, 2836 posts, 
A 1/5 to 1/4 percent fuel burn increase for about an 8 db noise reduction.
From Ireland, joined Jun 2006, 3288 posts, 
From United Kingdom, joined Jan 2005, 8610 posts, 
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