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1337Delta764
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RR BR715 (717) Thrust Reversers Question

Wed Jul 11, 2012 10:18 pm

I have a question about the thrust reversers on the RR BR715 engines on the 717. The BR715s on the 717 use clamshell thrust reversers, unlike most high-bypass turbofans which use cascade reversers. What is the reason for this?

I am pretty sure that on low-bypass engines, cascade reversers would not be possible, but what advantage does clamshell thrust reversers have over cascade for high-bypass engines?
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Mir
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RE: RR BR715 (717) Thrust Reversers Question

Wed Jul 11, 2012 10:38 pm

Clamshell reversers are more effective, since they direct the whole exhaust rather than just the bypass. But they're difficult to do when engines are mounted on the wings due to ground clearance and the presence of the wing itself.

Since the 717 has its engines mounted on the fuselage with no opportunity for disruption from the wing, clamshell reversers are the logical choice.

-Mir
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Viscount724
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RE: RR BR715 (717) Thrust Reversers Question

Wed Jul 11, 2012 10:39 pm

Quoting 1337Delta764 (Thread starter):

I am pretty sure that on low-bypass engines, cascade reversers would not be possible

The JT3D, a low-bypass turbofan, as used on the DC-8-50 and -61 series, had cascade reversers.
 
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1337Delta764
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RE: RR BR715 (717) Thrust Reversers Question

Wed Jul 11, 2012 10:56 pm

Quoting Mir (Reply 1):
Clamshell reversers are more effective, since they direct the whole exhaust rather than just the bypass. But they're difficult to do when engines are mounted on the wings due to ground clearance and the presence of the wing itself.

Since the 717 has its engines mounted on the fuselage with no opportunity for disruption from the wing, clamshell reversers are the logical choice.

-Mir

The MD-90 (which has tail-mounted engines) has cascade reversers, and the 737 Jurassic (which has wing-mounted engines) has clamshell reversers. I don't see what you mean here.
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NWADC9
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RE: RR BR715 (717) Thrust Reversers Question

Wed Jul 11, 2012 11:44 pm

Quoting 1337Delta764 (Reply 3):
The MD-90 (which has tail-mounted engines) has cascade reversers

They're the same IAE engines used on the A32X. Doubt they would engineer a different thrust reversing system for a specific aircraft type that decided to be the oddball.

Quoting 1337Delta764 (Reply 3):
and the 737 Jurassic (which has wing-mounted engines) has clamshell reversers

The clamshell doors are aft of the wing, not under it.
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1337Delta764
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RE: RR BR715 (717) Thrust Reversers Question

Thu Jul 12, 2012 12:12 am

Quoting NWADC9 (Reply 4):
They're the same IAE engines used on the A32X. Doubt they would engineer a different thrust reversing system for a specific aircraft type that decided to be the oddball.

Interesting though that CFM used target-type (flower petal) thrust reversers on the A320 family and first-gen A340, while they used cascade reversers on the 737. I'm guessing the reason for using cascade reversers on the 737 might be due to ground clearance. I wonder what will the LEAP-1A engines on the A320neo will use.
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Mir
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RE: RR BR715 (717) Thrust Reversers Question

Thu Jul 12, 2012 12:23 am

Quoting 1337Delta764 (Reply 3):
The MD-90 (which has tail-mounted engines) has cascade reversers

The engines were already designed with cascade reversers - it's not worth redoing the design for just one aircraft type.

Quoting 1337Delta764 (Reply 3):
the 737 Jurassic (which has wing-mounted engines) has clamshell reversers

And that's only possible because the engine passed all the way underneath the wing, and they were able to rotate it enough to get the appropriate ground clearance. Not something you could reproduce on a modern design.

-Mir
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