VC10er
Topic Author
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Joined: Tue Feb 20, 2007 6:25 am

Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 3:51 pm

NOVICE HERE!

Aircraft engine nacelles fascinate me, I wish I could get closer (when off   ) because I have a few specific questions:
Anyone willing to take the time to explain in lay terms would hold a special place in my heart and helping me become a "know it all"!!!

1- the cone in the back. I have a vague idea of why, I think having to do with very low air pressure at great heights and why are the blue upon delivery? AND why are some engines designed without them? Example: on a CRJ, cones, on an ERJ 145 NO cones and no layers either: just round hole? Same on some 747's.

2- the circular concentric openings (like a wedding cake on it's side) does thrust come from those rings around the cone? Or just the center?

3- the "bat wing" or "shark teeth" on the new 787 and 747-8? What function do they have? And why not on Airbus AC? are they patented for Boeing only? May we see them on the A350?

4-last question...I've noticed some leading edges on engines that are either matte or dull silver and on some, SUPER SHINY chrome. I recall seeing an RG MD-11 with 3 mirror-like rings on the opening to their 3 nacelles. But never on a 777? Or A330?

THANKS FOR ANY HELP! and I promise to tell people at the dinner table when the conversation turns to flying! VC10er
The world is missing love, let's use our flights to spread it!
 
my235
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RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 7:37 pm

This is trying to answer #1: The cone (or no cone) at the back of an engine is for mixing the fast moving hot exhaust with the slower moving bypass cold air. In doing so the noise produced by the engine is greatly reduced. Rolls Royce engines like the RB-211 on some 747's and 757's, have no cones. The mixing is done inside the nozzle.
 
tdscanuck
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RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 7:42 pm

Quoting VC10er (Thread starter):
1- the cone in the back. I have a vague idea of why, I think having to do with very low air pressure at great heights

It improves the aerodynamics of the flow coming out of the back of the engine. If you didn't have the cone you'd have a lot of recirculaton (lost energy).

Quoting VC10er (Thread starter):
and why are the blue upon delivery?

When the engine is running they're *hot*. Since the engine was run prior to delivery, the metal gets hot enough to get heat bluing. Most of the engine case looks the same way, you just can't see that because it's covered by the nacelle.

Quoting VC10er (Thread starter):
AND why are some engines designed without them? Example: on a CRJ, cones, on an ERJ 145 NO cones and no layers either: just round hole? Same on some 747's.

The cone is still there; the outer nacelle (the fan duct) just comes far enough back to cover it up.

Quoting VC10er (Thread starter):
2- the circular concentric openings (like a wedding cake on it's side) does thrust come from those rings around the cone? Or just the center?

The outermost ring (the big one) is the fan duct; most of the thrust comes from here. The inner big ring is the core duct. Typically about 20% of the thrust on a modern engine is coming from here. On some designs there may be a very thin ring between the core and fan ducts...no thrust from here, it's just the joint between the thrust reverser inner wall and the engine core. The small hole at the very center (not present on all designs) is to vent the engine centerline and provides essentially no thrust.

Quoting VC10er (Thread starter):
3- the "bat wing" or "shark teeth" on the new 787 and 747-8? What function do they have?

Noise reduction.

Quoting VC10er (Thread starter):
And why not on Airbus AC? are they patented for Boeing only? May we see them on the A350?

Airbus hasn't designed a new nacelle since chevrons were developed, so there isn't too much to be read into that yet. Boeing may have a patent but patents of that type are often fairly easy to bypass. That said, I can't find any art of the A350 showing chevrons, so Airbus may not be using them. You pay a small drag (read: fuel) penalty to have them, in return for lower noise.

Quoting VC10er (Thread starter):
4-last question...I've noticed some leading edges on engines that are either matte or dull silver and on some, SUPER SHINY chrome. I recall seeing an RG MD-11 with 3 mirror-like rings on the opening to their 3 nacelles. But never on a 777? Or A330?

From the factory they're matte (it's a brushed finish). Operators can choose to polish them...you tend to see this often on business jets and other aircraft where there is ample time to maintain it and appearance is a bigger factor.

Tom.
 
BMI727
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RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 7:50 pm

Quoting VC10er (Thread starter):
- the circular concentric openings (like a wedding cake on it's side) does thrust come from those rings around the cone? Or just the center?

Both. Usually the outer one is where the bypass air leaves the nacelle and the inner one (often the cone shape) is where the core exhaust is.

Quoting VC10er (Thread starter):
3- the "bat wing" or "shark teeth" on the new 787 and 747-8?

The low pitched roaring or rumbling sound you hear from a jet engine is the shearing between layers of hot, fast moving exhaust air and the cold, slower freestream air. There are a few ways to reduce this (other than reducing thrust).

First, add bypass air. In that case, you shroud the hot exhaust air with colder, slower bypass air, but not quite as cold and slow as the freestream. This helps blend the layers together with less shearing and less noise.

The chevrons on the back of the nacelle do the same sort of thing. They are shaped to help the different streams of air mix more effectively to reduce noise.

Quoting VC10er (Thread starter):
And why not on Airbus AC?

I could have sworn that chevrons were used on at least one non-Boeing aircraft, but I can't find it at the moment. I don't think they are limited to Boeing.
Why do Aerospace Engineering students have to turn things in on time?
 
MD11Engineer
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RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 7:55 pm

Quoting tdscanuck (Reply 2):
Quoting VC10er (Thread starter):
And why not on Airbus AC? are they patented for Boeing only? May we see them on the A350?

Airbus hasn't designed a new nacelle since chevrons were developed, so there isn't too much to be read into that yet. Boeing may have a patent but patents of that type are often fairly easy to bypass. That said, I can't find any art of the A350 showing chevrons, so Airbus may not be using them. You pay a small drag (read: fuel) penalty to have them, in return for lower noise.

I´ve seen at least one Antonov AN-124 using engines with chevrons at the fan exit.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
gigneil
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Joined: Fri Nov 08, 2002 10:25 am

RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 8:33 pm

Quoting BMI727 (Reply 3):
I could have sworn that chevrons were used on at least one non-Boeing aircraft, but I can't find it at the moment. I don't think they are limited to Boeing.

EJets have chevrons on their engines.

NS
 
DC8FriendShip
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RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 10:42 pm

Quoting BMI727 (Reply 3):
I could have sworn that chevrons were used on at least one non-Boeing aircraft, but I can't find it at the moment. I don't think they are limited to Boeing.

CRJ-900's also.
Come fly the Friendly Skies of United
 
BMI727
Posts: 11099
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RE: Airplane Nacelles: Why So Many Differences?

Sun Sep 11, 2011 11:27 pm

Quoting gigneil (Reply 5):
Quoting DC8FriendShip (Reply 6):

Yep, that's what it was. Anyway, the 787 and 747-8 take it to a higher level by utilizing the chevrons between the bypass and freestream, as opposed to between the hot section and bypass like the CRJ and E-Jets, which is why they are much more noticeable.
Why do Aerospace Engineering students have to turn things in on time?
 
gigneil
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Joined: Fri Nov 08, 2002 10:25 am

RE: Airplane Nacelles: Why So Many Differences?

Mon Sep 12, 2011 6:27 pm

Quoting DC8FriendShip (Reply 6):
CRJ-900's also.

I was gonna say that... but then I looked at a bunch, and they do not - at least not all of them. Perhaps just NextGens?

Edit: yeah that's not right. Its just hard to see in the pictures. Its much clearer on the EJets.

NS

[Edited 2011-09-12 11:29:02]
 
tepidhalibut
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RE: Airplane Nacelles: Why So Many Differences?

Wed Sep 14, 2011 9:48 pm

Quoting BMI727 (Reply 3):
Quoting VC10er (Thread starter):And why not on Airbus AC? are they patented for Boeing only? May we see them on the A350?
Airbus hasn't designed a new nacelle since chevrons were developed, so there isn't too much to be read into that yet. Boeing may have a patent but patents of that type are often fairly easy to bypass. That said, I can't find any art of the A350 showing chevrons, so Airbus may not be using them. You pay a small drag (read: fuel) penalty to have them, in return for lower noise.

Oh Really?

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Admittedly, it's their in-house prototype aircraft, so they were just investigating cost/weight/noise/operability effects.
 
tdscanuck
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RE: Airplane Nacelles: Why So Many Differences?

Thu Sep 15, 2011 2:52 am

Quoting tepidhalibut (Reply 9):
Admittedly, it's their in-house prototype aircraft, so they were just investigating cost/weight/noise/operability effects.

Exactly. By that metric Boeing was running chevrons in 2005.

Tom.

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