BR715-A1-30
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CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 4:11 pm

If you look at the early DC-10s engines from the 70s, It looks like there is a flat piece where the exhaust cone is today.

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Photo © Frank C. Duarte Jr.



But then if you look at the DC-10s of today, even the -10 models, that "flat piece" is no longer there, and has been replaced with the conventional cone. Can anybody tell me why this is? What was the purpose of this design?

Thanks

[Edited 2008-03-04 08:20:29]
Puhdiddle
 
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jetmech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 4:53 pm



Quoting BR715-A1-30 (Thread starter):

From the looks of the photo, it seems that this particular engine has thrust reversing on the core flow as well as the bypass flow. I assume that the flat piece allows the entire cone part to translate backward, which also actives the core reverser buckets. Most if not all newer turbo fans have done away with core reversing, so this may explain why the flat piece is not apparent through the exhaust cone on newer DC-10's.

Regards, JetMech
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BR715-A1-30
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 5:20 pm

Wow... Thanks JetMech... It would be interesting to see a core reverser in action on a CF6/JT9D. Are there any pictures out there?
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jetmech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 5:40 pm



Quoting BR715-A1-30 (Reply 2):

I must confess that I am only taking an educated guess with respect to your question. I do know that some early turbofans had core reversing, such as the JT3 on the 707. I'm really not sure for the CF6-6. I could not find any pictures of the CF6-6 with this particular exhaust cone in reverse.


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Regards, JetMech
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DC-10Tech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 7:10 pm

That's right, Jet Mech. The DC-10's originally had a turbine reversing system on its engines. The system was deactivated at some time and then eventually removed altogether. There's still references and info on this system on some companies' microfilm maintenance manuals.
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HAWK21M
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 9:03 pm



Quoting DC-10Tech (Reply 4):
The system was deactivated at some time and then eventually removed altogether.

Any reason for that.Was it ineffective or problematic?
regds
MEL.
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113312
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 9:26 pm

Hot stream reverse was abandoned on high bypass turbofans, such as the CF-6 series, at a relatively early point in their use. Since the percentage of thrust from the cold stream (bypass) increased, it was considered that the mechanics of deflecting the hot stream were not worth it.
 
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jetmech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 9:40 pm



Quoting HAWK21M (Reply 5):
Any reason for that.Was it ineffective or problematic?

Pretty much what 113312 says. The JT3D-3 was very low bypass, with a ratio of only about 1.4:1, thus; core reversing would provide a significant amount of the total reverse thrust. The CF6-50 has a bypass ratio of 4.26:1, the CF6-80C2 5.15:1, with the GE90-115B having a bypass ratio of 9:1. Thus, the core reversing on newer turbofans would only provide a very small amount of reverse thrust.

Regards, JetMech
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DC-10Tech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Tue Mar 04, 2008 11:16 pm



Quoting HAWK21M (Reply 5):
Any reason for that.Was it ineffective or problematic?

Both.
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aloges
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Mar 05, 2008 1:20 am

Are the RR Tays on the Fokker 70/100 the last engines to reverse both core and bypass (on commercial airliners)?
Don't cry because it's over, smile because it happened.
 
boeing767mech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Mar 05, 2008 1:56 am



Quoting Aloges (Reply 9):
Are the RR Tays on the Fokker 70/100 the last engines to reverse both core and bypass (on commercial airliners)?

I think the MD90/95 B717 also has fan/core thrust reversors. Which the MD95/717 finished production long after Fokker went out of business, I also think the ARJ-21 has core/fan reversors like the MD90/95.

David
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N231YE
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Mar 05, 2008 2:12 am

As some have already stated, that is/was the core thrust reverser mechanism. Like those found on the early JT9Ds, they were deleted in later models, deactivated and/or removed in the early models. I have some drawings of the CF6-6 reverser on the DC-10-10 if you'd like (me to post).
 
avioniker
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Mar 05, 2008 4:05 am

The BR715 as well as the JT8 engine have clamshell reversers which simply deflect all air out of the engine forward or, more accurately, not aft.
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aloges
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Mar 05, 2008 10:15 am

Thanks! I hadn't thought of the later MDs and the 717.
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F14D4ever
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Thu Mar 06, 2008 1:13 pm



Quoting Boeing767mech (Reply 10):
I also think the ARJ-21 has core/fan reversors[sic]

Negative. The ARJ-21 is powered by the GE CF34-10A, which is a 70% scale of the CFM56. Neither the CF34-10, nor the CFM, have core reversing.
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ex52tech
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Sat Mar 08, 2008 5:05 am



Quoting HAWK21M (Reply 5):
Was it ineffective or problematic?

A lot of delays, and a mechanics nightmare, I was more than happy to deactivate those........ah........fine pieces of equipment..
Even the deactivated tailpipes caused some problems until the dedicated tail pipes came out, then the trouble finally went away.
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Buzz
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Sat Mar 08, 2008 12:47 pm

Hi MEL, Buzz here. The Turbine Reversers on the CF6 engines would cause a lot of problems...hard to keep the mechanism running well. So as the engines cycled through the shop the turbine reverser mechanism was removed.

And... the reference was still in the Maint. Manual and A check paper package.

g'day
 
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Sat Mar 08, 2008 3:30 pm



Quoting Ex52tech (Reply 15):
And... the reference was still in the Maint. Manual and A check paper package

We ran about 50% of the fleet on deactivated turbine reversers, and the deactivated reversers got neglected. They would occasionally remind you that they were there when the bolts that held them shut would wear down spinnning in the holes, then break off and the translating tail pipe would deploy.........and then depart the aircraft.
This all started to happen when the heavy checks got farmed out. We kept an eye on them in heavy check.........they didn't.  Wow!
An airplane would show up at the gate with no tailpipe, and no conical nozzle, or center body. Management would blame us, when they farmed it out.  banghead 
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Northwest727
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Fri Nov 19, 2010 11:05 pm

Sorry about bringing this post up from the dead, I saw it at the bottom of the screen, and thought I'd add to it

Quoting JetMech (Reply 1):
I assume that the flat piece allows the entire cone part to translate backward, which also actives the core reverser buckets.

JetMech, the cone part stayed fixed, it was the flat "blade" that slid backwards, which exposed a set of cascades that would "pop-out" into the core flow:

CF-6 Core Thrust Reverser
 
kiwiandrew

RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Sun Nov 21, 2010 7:47 am

Quoting BR715-A1-30 (Thread starter):
If you look at the early DC-10s engines from the 70s, It looks like there is a flat piece where the exhaust cone is today.

Thanks for starting this thread , I have wondered about that for a long time , but never actually thought to ask on here . Glad to have my question answered after 30 years   
 
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Sun Nov 21, 2010 11:51 pm

Quoting Northwest727 (Reply 18):

Thanks for the info! What an interesting design. You would never think anything so delicate as those vanes could withstand the heat and force of the core exhaust stream!

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
Northwest727
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Mon Nov 22, 2010 3:52 am

Quoting jetmech (Reply 20):

Glad to see you liked the info. By the way, I always enjoy reading your posts, good info you put on here yourself!

As for the delicate vanes, I'm not sure they even could withstand the heat and force of the core exhaust stream, that's why they were later removed  
 
Fly2HMO
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Mon Nov 22, 2010 5:13 am

Quoting Northwest727 (Reply 21):

As for the delicate vanes, I'm not sure they even could withstand the heat and force of the core exhaust stream, that's why they were later removed

Probably just not worth the extra MX, weight and cost, as it always is with these type of things.
 
kiwiandrew

RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Mon Nov 22, 2010 6:05 am

Was this only on the number 2 engine ? I don't recall ever noticing it on other engines.
 
access-air
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Dec 08, 2010 4:03 pm

Quoting kiwiandrew (Reply 23):
Was this only on the number 2 engine ? I don't recall ever noticing it on other engines.

It was on all three engines....

Actually the L1011 also was first produced with a bucket type system on the core stream section of the ole RB211s...

Access-Air
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Northwest727
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Wed Dec 08, 2010 6:32 pm

Quoting Access-Air (Reply 24):
Actually the L1011 also was first produced with a bucket type system on the core stream section of the ole RB211s...

You can see the "tracts" for the core stream thrust reversers on the L1011 in the photo


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kiwiandrew

RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Thu Dec 09, 2010 5:25 am

Quoting Access-Air (Reply 24):
It was on all three engines....

Thanks for that ,    when I look at photos in the database I can see it on numbers 1 and 3 in some photos ... it is just a lot more obvious on the number 2 engine
 
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Faro
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Thu Dec 09, 2010 9:12 am

Quoting Buzz (Reply 16):
The Turbine Reversers on the CF6 engines would cause a lot of problems...hard to keep the mechanism running well. So as the engines cycled through the shop the turbine reverser mechanism was removed.
Quoting Ex52tech (Reply 15):
A lot of delays, and a mechanics nightmare, I was more than happy to deactivate those........ah........fine pieces of equipment..
Quoting Ex52tech (Reply 17):
We ran about 50% of the fleet on deactivated turbine reversers, and the deactivated reversers got neglected. They would occasionally remind you that they were there when the bolts that held them shut would wear down spinnning in the holes, then break off and the translating tail pipe would deploy.........and then depart the aircraft.

So what has changed since the early 1970's to make MD/Boeing go back to turbine thrust reversers on the C-17's PW engines, or can we assume that these are also a maintenance nightmare?

Faro
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tdscanuck
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RE: CF6-6 Engine On DC-10... Why The Weird Cone?

Thu Dec 09, 2010 2:10 pm

Quoting faro (Reply 27):
So what has changed since the early 1970's to make MD/Boeing go back to turbine thrust reversers on the C-17's PW engines, or can we assume that these are also a maintenance nightmare?

I'd hope they learned something and they're not as much of a maintenance nightmare, but I fully expect them to be a pain in the a$$. The C-17 has an overriding short-field requirement that makes that extra work/cost/parts worth it...that requirement doesn't exist for large commercial jets.

Tom.

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