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Thrust Reverse Types

Mon Feb 16, 2004 1:38 am

Do some designs work better than others or more effective?
What lead me to ask the question is that on some airbus a/c some have the standard full 360 shroud moving back and some have the reverse setup as 4 doors opening at 10-2-4-8 o'clock.
Clamshell vs. cascade as well.

"And remember, Keep your stick on the ice"--->Red Green
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RE: Thrust Reverse Types

Mon Feb 16, 2004 9:08 am

Cascade reversers are the first you mentioned where the engine casing goes back and lets bypass flow come out in the forward direction. Since they only use bypass air as a reverse thrust generator, there is still idle core thrust being produced that counteracts a little of this reverse thrust. The clamshell and bucket type reversers reverse the entire flow (both bypass and core) and therefore are a bit more effective. I don't have too much information to get technical on the issue, but I hope this information helps you!

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RE: Thrust Reverse Types

Wed Feb 18, 2004 8:54 am

There was also the petal-type reversers you mentioned, with the 4 doors.

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RE: Thrust Reverse Types

Wed Feb 18, 2004 8:56 am

To answer the second part of your question, one would argue that clamshell reversers are somewhat more effective, as they divert 100% of the engine exhaust.
I got my head checked--by a jumbo jet
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RE: Thrust Reverse Types

Wed Feb 18, 2004 10:42 am

It is amazing you just asked this as I was thinking the same thing after looking at a pic of the A-320 reversers. My follow up question to this would be: Does diverting all thrust in the clamshell style result in any extra wear and tear or corrosion on the tailpipe/wing?
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RE: Thrust Reverse Types

Thu Feb 19, 2004 10:11 am

Do the GE90 series engines have both the bypass and core reversing at the same time, and would a clamshell type reverser be more effective on this type?

Appreciate the info guys!!!
"And remember, Keep your stick on the ice"--->Red Green
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RE: Thrust Reverse Types

Thu Feb 19, 2004 11:19 pm

The GE90 uses cascade reversers only. Yes, a clamshell reverser for the core would increase reverse thrust, but with the large bypass ratio of the GE90 the overall gain in reverser effectivity would be relatively small compared to smaller engines. Also, clamshells on a GE90 would weigh a lot. It's a trade-off, the increase in reverse thrust is not worth the increase in engine weight.

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RE: Thrust Reverse Types

Fri Feb 20, 2004 1:15 am

Thanks Darkblue!!!!

Does anybody have a sketch or diagram of how the CFM ( I think its CFM ) works with the 4 doors that open for reverse. Is this type only a special request by some airlines or determined by airbus?
"And remember, Keep your stick on the ice"--->Red Green
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RE: Thrust Reverse Types

Wed May 26, 2004 2:11 am

Was just about to ask a similar question, but I found this thread and it seems relevant so I'll ask it in here.

Am I right in thinking the RR Trent 600, 800 and 900 series have cascade thrust reversers? And if so, why does the 700 series, as in use on the A330, have the four-door petal "pop-up" type described above? Is there a fundamental design difference in the engine that requires this? Or is more to do with the shaping of the engine cowling due to aerodynamic requirements, that is the main reason?

It is indeed the CFM56-5 series in use on the A320 and A340 family that has that type of reverser. Regarding it being a special request by airlines - that is not the case. If the airlines order CFM engines, then that is the kind of reverser they come with, unlike the IAE which has the cascade type. The CFM56-3 and 56-7 on the 737, however, also have the cascade type. (As for the first part of your question, I'm unable to answer that I'm afraid, but I'm sure there's someone who can!)

[Edited 2004-05-25 19:12:37]
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RE: Thrust Reverse Types

Wed May 26, 2004 6:54 am


"Target" or "Bucket" or "Clamshell" reversers

Two or more clamshell deflector panels which redirects exhaust air forward. Their use is mainly on older turbojet engines, or very low bypass turbofans. Not many higher-bypass turbofans use clamshell reversers for a few reasons. One is that, like DarkBlue mentioned, they would have to be very large and heavy, and impractical on the whole. Another consideration is that, depending on the particular aircraft and engine, clamshell doors could actually hit the ground when deployed. Overall, clamshell reversers are more effective than other types (given the same engine), but not always what works best, of course.

^Clamshell reverser

"Cascade" reversers

A combination of panels to block bypass flow and opening vents on the sides of the engine to give the bypass air a place to exit. There are vanes in the vents, which redirect the flow forwards. Cascade reversers are a more practical reverse thrust mechanism for high-bypass turbofans than clamshell reversers, for the reasons mentioned already. Not many (or any, maybe?) low-bypass engined aircraft employ cascade reversers simply because there's not enough bypass air to slow the aircraft effectively enough.

^Cascade reverser

"Petal" reversers

A variation on the cascade reverser. Bypass air is redirected out of a vent and forward (by the petals). Like the cascade reverser, petal reversers are usually only used on high-bypass engine aircraft.

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RE: Thrust Reverse Types

Wed May 26, 2004 7:38 am

See - I told you there was someone who could answer!

Cheers, QantasA332  Smile
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RE: Thrust Reverse Types

Wed May 26, 2004 12:24 pm

Cool graphics Qantas!!!!!!  Smile Smile

FlytoEGCC thanks for getting this thread jump started again!!  Smile

Thanks everyone for the information.

Best Regards,

"And remember, Keep your stick on the ice"--->Red Green
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RE: Thrust Reverse Types

Sat May 29, 2004 8:34 am

Thrust reverser design is a bit of a black art. The 360 deg cascade on most aircraft are rather complicated because the cascades need to be designed with respect to the location on the engine. Those at the bottom of the engine try to direct the flow sideways rather than directly forward so that any debris isn't blown back onto the engine nacelle or reingested. Similarly those that might blow onto a surface on the aircraft (like on the CRJ700 where the fuselage and horizontal stabilizer might be affected) need to direct the flow away as well as forwards.

The 4 door version on the CFM engines avoids this problem. It also has the advantage that they are solid deflector doors that will act as air brakes which are more efficient than just a jet directed forwards, so the area they occupy is smaller.

The bucket reversers on the 737-200 used to be vertical before it was found that the reverse thrust directed straight down was affecting braking performance.

The ironic thing about reversers is that they are not part of any certification process, the aircraft should be able to land and stop on the brakes alone. They are there to reduce the runway length for landing and increase brake life.

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RE: Thrust Reverse Types

Sat May 29, 2004 11:15 am

The Citation X (Model 750) has clamshell reversers. During development testing, it was discovered that the nose gear could come off the ground under light weight, high thrust reversing. The solution was to put "spacers" at the back of the clamshells so that they wouldn't completely contact and close off the reverse flow. This reduced the effectiveness of the reversers and kept the nose gear on the ground.

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