c5load
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Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 2:59 am

I was looking at pictures of the 787 and the new 747-800 and was curious as to the cookie-cutter design in the back of the engine? Is it something to do with its performance or is for looks? I tried posting the pics, but it won't work for some reason so here are the links.

http://www.airliners.net/photo/Boein...Boeing-787-8-Dreamliner/1630532/L/

http://www.airliners.net/photo/Boeing/Boeing-747-8R7F-SCD/1649963/L/
"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
 
BMI727
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 3:06 am

Quoting C5LOAD (Thread starter):
Is it something to do with its performance or is for looks?

The chevrons are there to reduce noise. The shapes at the back of the pylon help mix the ambient air and the air from the engine more smoothly and effectively. The interactions between these two streams of air is responsible for the roaring sound you hear from an engine and the chevrons will help reduce that.

This is the same reason why higher bypass engines are quieter as well. The bypass air shrouds the exhaust.
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skyone
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 3:08 am

Don´t know, but it shure looks nice!!! I really like it. It is one of those things that makes things look more modern than its similars of the past, like in the case of the 747-800 vs. 747-400.
 
ArabAirX
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 10:27 am

I think the design was first trialled on a 777-300ER.
 
BrouAviation
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 10:33 am

I also believe it adds a little bit of fuelburn, as induced drag increases, and vortices will form easier.

Quoting BMI727 (Reply 1):
The interactions between these two streams of air is responsible for the roaring sound you hear from an engine and the chevrons will help reduce that.

You are correct, but:
Don't want to nitpick, but doesn't this cause the screaming sound? The roar is only heard in front of the engine, and is actually caused by the engine itself?
Of course it depends on what you define as 'screaming' and 'roaring'.
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MadameConcorde
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 10:38 am

This is one of the first things I noticed on the new aircrafts, the jigsaw design on the engines and I had not the slightest idea why they had done this. My first idea was so they looked different, though appartently there is a truly practical reason to this "cookie-cutter" design. Now I know more, thanks to this thread!    ^^^^^^^^^^
There was a better way to fly it was called Concorde
 
ArabAirX
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 11:04 am

Quoting BrouAviation (Reply 4):
I also believe it adds a little bit of fuelburn

Not sure that it does according to link below:

http://www.boeing.com/news/frontiers/archive/2006/march/i_tt.html

Not recent but still a worthy read.
 
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747classic
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 11:08 am

Quoting BrouAviation (Reply 4):
I also believe it adds a little bit of fuelburn, as induced drag increases, and vortices will form easier.

At the moment approx 0.25 % specific fuel consumption (SFC) loss, caused by chevrons, is demonstrated.
In the future this loss can be eliminated by temperature depended chevrons. Using shape memory alloys, the chevrons will be able to bend in and out of the flow exactly as needed. Activated by temperature, the tabs can be told when to change shape based on the atmospheric conditions at takeoff and cruise altitude. Already they've been tested on a GE-90 engine on a Boeing 777, the first commercial application of a morphing structure.

see : http://www.memagazine.org/backissues.../nov06/features/nozzle/nozzle.html
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
ArabAirX
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 11:49 am

Does anyone know if such a design will be used on the Trent XWB engines for the A350?
 
BMI727
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 4:36 pm

Quoting BrouAviation (Reply 4):
The roar is only heard in front of the engine, and is actually caused by the engine itself?

I think you have it backwards.

The two components (which I will scientifically refer to as the scream and the roar) have two causes. The scream, which is heard more in front of the engine, is due to the interation between the air and the fan (or compressor in a turbojet) blades. This is the sound that can turn into a loud buzzing sound with the blade tips go beyond the speed of sound.

The roar is caused by the turbulent interaction between the ambient atmosphere and the jet exhaust and is heard mostly from behind the engine. This sound is alleviated by having a high bypass ratio now by adding chevrons to the rear of the nacelle, which helps the streams of air mix more smoothly and quietly.
Why do Aerospace Engineering students have to turn things in on time?
 
cobra27
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 4:51 pm

Could it be that is also to emphasise something different?
 
Birdwatching
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 5:27 pm

Why are you calling this a "cookie cutter" design?

It has no similarity to a cookie cutter.

Soren   
All the things you probably hate about travelling are warm reminders that I'm home
 
c5load
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 5:38 pm

Quoting Birdwatching (Reply 11):
Why are you calling this a "cookie cutter" design?

What would you call it? Sawblade?
"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
 
Birdwatching
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 5:44 pm

Quoting C5LOAD (Reply 12):
What would you call it? Sawblade?

Much better. I tried to figure out how you would cut cookies with this. Not possible. Your "engine cookies" would still stick to the rest of the dough around them. In fact you could cut cookies much better with a conventional engine design.

That being said... mmmmm, cookies.

Soren  santahat 

[Edited 2010-02-10 10:01:52]
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ba1978
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 5:45 pm

Quoting C5LOAD (Reply 12):
uoting Birdwatching (Reply 11):
Why are you calling this a "cookie cutter" design?

What would you call it? Sawblade?

I think they're referred to as chevrons.
There are other ways and there's British Airways
 
ba1978
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 6:04 pm

Quoting Birdwatching (Reply 11):
Why are you calling this a "cookie cutter" design?

It has no similarity to a cookie cutter.
Here's your cookie cutter!
There are other ways and there's British Airways
 
keta
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 8:14 pm

Quoting BrouAviation (Reply 4):
Don't want to nitpick, but doesn't this cause the screaming sound? The roar is only heard in front of the engine, and is actually caused by the engine itself?
Quoting BMI727 (Reply 9):
The roar is caused by the turbulent interaction between the ambient atmosphere and the jet exhaust and is heard mostly from behind the engine. This sound is alleviated by having a high bypass ratio now by adding chevrons to the rear of the nacelle, which helps the streams of air mix more smoothly and quietly.

   The exhaust causes a low frequency (which is what I understand as roaring) noise due to the turbulence of the mixing flow. Higher bypass reduces exhaust speed and chevrons improve the mixing conditions, both of which help reduce noise.

Quoting ArabAirX (Reply 8):
Does anyone know if such a design will be used on the Trent XWB engines for the A350?

Airbus' renderings of the A350 don't show any kind of serrations on the engines, but who knows...

On the other hand, I recall Airbus stating that they achieved some noise reduction in the A380 by an improved engine inlet, which did not have a negative effect on fuel consumption. If this works, they'll include this design in the A350. I don't have more info, though...

Quoting 747classic (Reply 7):
At the moment approx 0.25 % specific fuel consumption (SFC) loss, caused by chevrons, is demonstrated.
In the future this loss can be eliminated by temperature depended chevrons. Using shape memory alloys, the chevrons will be able to bend in and out of the flow exactly as needed. Activated by temperature, the tabs can be told when to change shape based on the atmospheric conditions at takeoff and cruise altitude. Already they've been tested on a GE-90 engine on a Boeing 777, the first commercial application of a morphing structure.

see : http://www.memagazine.org/backissues.../nov06/features/nozzle/nozzle.html

Awesome. Although I was expecting a more drastic morphing, something which radically changed the geometry. This is nothing but a thermostat 

[Edited 2010-02-10 12:15:35]
Where there's a will, there's a way
 
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Stitch
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 8:28 pm

Well they seem to work, as the 747-8 was quieter than the 777-300ER that departed before it. It also sounded quieter than I recall the 787-8 sounding.
 
Fly2HMO
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 11:32 pm

Quoting MadameConcorde (Reply 5):
My first idea was so they looked different,

Airplanes are ALWAYS designed with the form follows function philosophy. Nobody designs or modifies planes just to look pretty.

Of course, gorgeous planes still exist. Such as Concorde and the SR-71. A coincidence really that they turned out so sexy  
 
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Starlionblue
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RE: Cookie-Cutter Engine Design On The 787,748

Wed Feb 10, 2010 11:43 pm

Quoting 747classic (Reply 7):
At the moment approx 0.25 % specific fuel consumption (SFC) loss, caused by chevrons, is demonstrated.
In the future this loss can be eliminated by temperature depended chevrons. Using shape memory alloys, the chevrons will be able to bend in and out of the flow exactly as needed.

Wow. That sounds pretty sci fi.

I, for one, welcome our new memory alloy overlords.

Quoting Birdwatching (Reply 11):
Why are you calling this a "cookie cutter" design?

It has no similarity to a cookie cutter.

This did indeed confuse me, especially as "cookie cutter" is an expression referring to something unoriginal and/or uninspired.

[Edited 2010-02-10 15:44:42]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BMI727
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 2:26 am

Here are some clips that might shed more light on the subject.

http://www.youtube.com/watch?v=a80ark8Rpsk

When you watch the PIA 777 take off (about 1:10), you will notice that you hear more of the higher pitched sound in front of the plane and the roar of the exhaust becomes more prominent after it passes by.

http://www.youtube.com/watch?v=qMsyoX9Drwc

In this clip, you can hear the loud buzzing sound due to the fan blades breaking the sound barrier, starting at about 0:20.
Why do Aerospace Engineering students have to turn things in on time?
 
jetlife2
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 3:08 am

This article describes the acoustic testing we did putting various chevrons (including the actuated shape memory material) on a GE90-115B/777-300ER, as well as other engine and airframe modifications

http://www.boeing.com/news/frontiers...archive/2005/december/ts_sf07.html
My views are not necessarily the views of the GE Company
 
keta
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 9:34 am

Quoting jetlife2 (Reply 21):
This article describes the acoustic testing we did putting various chevrons (including the actuated shape memory material) on a GE90-115B/777-300ER, as well as other engine and airframe modifications

http://www.boeing.com/news/frontiers....html

Very interesting read, thanks! It's also interesting the work on the landing gear, never heard of that before.
Where there's a will, there's a way
 
cobra27
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 11:06 am

Quoting Birdwatching (Reply 11):
Why are you calling this a "cookie cutter" design?

It has no similarity to a cookie cutter.

You know what is also funny: calling jet engine hairdriers
 
MD11Engineer
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 4:06 pm

I´ve seen a few AN-124s at our airport using similar reverser cowls, but I didn´t take a picture.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
kit777
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 4:19 pm

Quoting FLY2HMO (Reply 18):

You seem to be forgetting the most beautiful airplane of them all, the A380  .

Back on topic though, I have also seen these chevrons on A320 series aircraft I think, either them or E-jets.

Here is a picture of one being tested on an A346 testbed:



Thanks

Kit
 
pilotpip
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 7:41 pm

The 170/190 and CRJ-900 CF-34s have them on the exhaust as well. None on the cowl like the 340 above.
DMI
 
kit777
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RE: Cookie-Cutter Engine Design On The 787,748

Thu Feb 11, 2010 7:48 pm

Quoting pilotpip (Reply 26):

Yeah, I was thinking of the exhaust section. I'm pretty sure some AF A320s have those too.

Thanks

Kit

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