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727glasair
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Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 6:20 am

I have always marveled at the visual mechanics of the clamshell type reversers on older 737 and 727 jets. I have several questions:

Did other engines also employ the clamshell system?
Was ground clearance one reason we don't see them any longer?
It seems these modern sliding nacelle type reversers would be less efficient?
Any likelyhood we will see these clamshell types again?

It appears that clamshell reversers create a true physical barrier that actually deflects the thrust backward....how does the modern sliding type actually reverse the thrust?
 
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BartSimpson
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 6:24 am

For clamshell type reversers the DC-9, Fokker 70 / 100, Ilyushin Il-62, Tupolev 154 come to mind.

PS: this site (http://aerospaceengineeringblog.com/thrust-reversal/) gives you a nice overview on the different reverser types.
 
WIederling
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 7:30 am

"It appears that clamshell reversers create a true physical barrier that actually deflects the thrust backward....how does the modern sliding type actually reverse the thrust?"

Same. Difference is that only the Bypass airstream is deflected. the core flow continues to go out the back.
(one) Advantage: The engine does not ingest its own exhaust ( too hot, lack of oxygen.).
 
opticalilyushin
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 8:08 am

I imagine part of it may come down to engine location. Nowadays aircraft typically don't use the class he'll design if the engines are mounted on low wings, I guess for fear of self-ingestion. This is less of an issue on tail mounted engines due to the added height and protection from the nearby wing
 
Dalmd88
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 9:05 am

It appears that clamshell reversers create a true physical barrier that actually deflects the thrust backward....how does the modern sliding type actually reverse the thrust?

The sliders open up the side of the reverser and actuate internal blocker doors for the bypass airflow. The bypass air flow tends to be the largest portion of the thrust of high bypass engines.
 
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LAX772LR
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 9:05 am

727glasair wrote:
clamshell reversers create a true physical barrier that actually deflects the thrust backward

You mean "frontward." And even then, there was still a considerable up/down angling.



BartSimpson wrote:
For clamshell type reversers the DC-9, Fokker 70 / 100, Ilyushin Il-62, Tupolev 154 come to mind.

Add Concorde to that list as well.
 
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Starlionblue
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 9:15 am

You can see here how modern reversers also deflect the flow somewhat frontward. However only the bypass flow.

Besides the ingestion issue, you avoid the whole "hot gases" issue and design complexity is reduced. With 90%+ of thrust from the fan you're getting most of the good stuff anyway.

Image

Image
 
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CarlosSi
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 9:20 am

Aside from reducing design complexity due to fewer hot surfaces, is there any efficiency to having the nacelle slide rather than just "clamming" it?
 
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Starlionblue
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 9:26 am

CarlosSi wrote:
Aside from reducing design complexity due to fewer hot surfaces, is there any efficiency to having the nacelle slide rather than just "clamming" it?


Hmmmm. I guess you're avoiding a massive door moving close to the ground. Ground clearance on many modern engines is not massive.
 
StereoTechque
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 10:07 am

Modern tail engine mounted business jets however are still using Clam shell type T/R due their relatively small size and simplicity
 
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rjsampson
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Re: Thrust Reversers: Clamshell vs Sliding Nacelle?

Mon Aug 14, 2017 5:31 pm

727glasair wrote:
It appears that clamshell reversers create a true physical barrier that actually deflects the thrust backward....how does the modern sliding type actually reverse the thrust?


Here's a good video of how a sliding/cascade type engine diverts thrust somewhat frontwards. As the nacelle slides back to open up the cascade, several angled doors block the bypass air:

http://www.youtube.com/watch?v=bvpj1BV-sCk

This is a RR Trent on a 777 which, for obvious reasons, could never utilize a bucket system.

Believe it or not, there's an even better visualization of this on YouTube -- using a 777 model that some mad-genius-artist built using only glue and manila folders, right down to major systems. This video demonstrates the GE-90 cascade reverse system in surprisingly excellent detail:

http://youtu.be/1LckG_P135Q?t=63

Hope this helps.

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