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c5load
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Which T/R Is The Most Efficient?

Wed Jan 20, 2010 2:51 am

I was looking at these images and wondered is there any difference in efficiency or amount of reverse power between the three?


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Photo © Botterman Bram
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Photo © Johan Knijn

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DashTrash
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 3:15 am

Clamshells like on the DC-9 by a longshot. They redirect more thrust forward, nearly 100% of the total thrust of the engine is redirected in some fashion. With the translating cowl reversers engine core thrust is not redirected. I'm not sure about the petal type on the Airbus but I imagine it's about the same way.
 
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Starlionblue
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 4:02 am

As DashTrash says. Petals and translating cowls only redirect bypass flow. This is less efficient that redirecting all the flow as on the the old clamshells.

Then again on modern engines the majority of the flow is bypass so you don't lose as much as you would on a DC-9, which has a bypass ration of 1:1 or something like that. Also the old clamshells required more maintenance and at a guess they are heavier. As usual, a compromise.
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tdscanuck
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 4:19 am



Quoting C5LOAD (Thread starter):
I was looking at these images and wondered is there any difference in efficiency or amount of reverse power between the three?

Reverse power (in descending order):
1) Clamshell
2) Translating sleeve
3) Petal

Clamshells are the worst for maintenance though...I suspect translating sleeve's are next but I'm not positive.

Petals are almost certainly the lightest.

It's all a giant trade study...efficiency, in this case, is all a question of "efficiency of *what*"?

Tom.
 
AA737-823
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 9:30 am



Quoting Starlionblue (Reply 2):
Also the old clamshells required more maintenance and at a guess they are heavier.



Quoting Tdscanuck (Reply 3):
Clamshells are the worst for maintenance though

Agreed- they're horrendous. The rigging is a nightmare, the forward stow stops are a nightmare, the aft stow stops are a nightmare, the locking mechanisms are a nightmare (and leak), and pilots LOVE to write up things like, "Reverser #1 indicated CLOSED one-half second after reverser #2."

That said, translating cowls are prone to FOD, especially snow, on short-cowl engines like the JT-9D on classic 747s and early 767-200s. When this happens, there's no heat (in the bypass duct) to keep things warm, and you soon find you've not only got a reverser that is stuck deployed, but it is now also FROZEN deployed.
I've spent many a long morning trying to convince 747-200F reversers to stow.

Curiously, the airline I worked for originally had core-stream reversers fitted, but had since removed them.
That begs the question: which is more effective, a clamshell, or a dual-stream translating reverser?
 
PGNCS
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 7:14 pm



Quoting AA737-823 (Reply 4):
Agreed- they're horrendous. The rigging is a nightmare, the forward stow stops are a nightmare, the aft stow stops are a nightmare, the locking mechanisms are a nightmare (and leak), and pilots LOVE to write up things like, "Reverser #1 indicated CLOSED one-half second after reverser #2."

That is interesting. I suspected they were difficult to maintain, but there is a definite consensus on this one.

I am curious about the pilot writeup comment, though. I have never in 19 years at my current airline (or others before the current one) seen a writeup for anything like that for a reverser. The pilots I know who fly with clamshell reversers seem to understand that they don't always work in perfect synchronization. If you did get a writeup like that, isn't there a specification that says what the tolerances are allowing you to sign off the aircraft saying it's in tolerance per whatever MX manual specifies that? Just curious.

All operators are certainly different, but in my experience most pilots try to write up things that are airworthiness items and items that are clearly working incorrectly, not trivial tolerances that are normal and expected.
 
Northwest727
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 7:24 pm



Quoting DashTrash (Reply 1):
With the translating cowl reversers engine core thrust is not redirected



Quoting Starlionblue (Reply 2):
Petals and translating cowls only redirect bypass flow. This is less efficient that redirecting all the flow as on the the old clamshells.

Just to add, many 707s, early DC-10s and early 747s (all using translating cowl reversers) also used core reverse; however, the added weight and maintenance costs did not justify their use.

707:


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DC-10:


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Photo © Frank C. Duarte Jr.





Boeing 747:


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Photo © Ellis M. Chernoff




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Photo © Ellis M. Chernoff

 
vikkyvik
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 7:29 pm



Quoting DashTrash (Reply 1):
Clamshells like on the DC-9 by a longshot. They redirect more thrust forward, nearly 100% of the total thrust of the engine is redirected in some fashion.

Just to clarify to avoid confusion - you might get about 100% of the airflow redirected in some fashion, but you won't be recouping 100% of the backward thrust as forward thrust, since the airflow is now at a significant angle upward and downward.

Hmmm, I'm not sure if I worded it any more clearly.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
474218
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 7:47 pm

It really depends on the engine. A high bi-pass like the RB-211 produces the majority of its thrust from the cold stream. Therefore having the clam shell reversers closing off the hot stream did little when compared to the translating cowl reversers. That is why the clam shell reversers were deleted from the RB-211's on the L-1011.

Clam shell reversers work best on low by pass engines.
 
stratosphere
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RE: Which T/R Is The Most Efficient?

Wed Jan 20, 2010 8:21 pm



Quoting PGNCS (Reply 5):
If you did get a writeup like that, isn't there a specification that says what the tolerances are allowing you to sign off the aircraft saying it's in tolerance per whatever MX manual specifies that? Just curious.

Yeah there are just like there are AMM references for a lot of write ups where there is nothing wrong with the A/C but it can be a MAJOR pain in the ass for us especially at departure because when it is in the book we need a proper AMM sign off to protect OUR butts and sometimes they are not easy to find. Add to that the mechanic may be far from a computer to look up the said reference. I cannot tell you how many times I had a pilot write something up that was not a big deal to him/her and said to me "It's no big deal you can just sign it off". Well what might not be a big deal to a pilot might be a major headache for us. I am not saying you do this but every now and then it happens..Also you have what I call the 1 percenters who will do it all the time just like there are the 1 percenters in every work group who like to make life miserable for their co-workers.
 
AA737-823
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RE: Which T/R Is The Most Efficient?

Thu Jan 21, 2010 2:21 pm



Quoting PGNCS (Reply 5):
I am curious about the pilot writeup comment, though. I have never in 19 years at my current airline (or others before the current one) seen a writeup for anything like that for a reverser. The pilots I know who fly with clamshell reversers seem to understand that they don't always work in perfect synchronization. If you did get a writeup like that, isn't there a specification that says what the tolerances are allowing you to sign off the aircraft saying it's in tolerance per whatever MX manual specifies that? Just curious.

I envy you and your pilots, they must be a dream to work with.
The pilots at my small private carrier (small and private, but still flying Boeings) are anything but a dream. Write ups such as this one are some of the more legitimate ones we receive.
And, for my carrier, the tolerances in the manual are COMPLETELY irrelevant- we must achieve perfection (at least, someone's view of perfection... which rarely coincides with my own view) every day, or the aircraft will be rejected in the morning, with no disciplinary action to the pilots whatsoever.

Quoting PGNCS (Reply 5):
All operators are certainly different, but in my experience most pilots try to write up things that are airworthiness items and items that are clearly working incorrectly, not trivial tolerances that are normal and expected.

Again, I long to work for your carrier. That said, my pay is pretty good, as is my job security! And, I love my job... it's just the pilots and F/A's that needs to spend 8 weeks with a real airline, and learn how things work in the real world. Not less safe, mind you... less stupid.

Quoting Stratosphere (Reply 9):
Yeah there are just like there are AMM references for a lot of write ups where there is nothing wrong with the A/C but it can be a MAJOR pain in the ass for us especially at departure because when it is in the book we need a proper AMM sign off to protect OUR butts and sometimes they are not easy to find. Add to that the mechanic may be far from a computer to look up the said reference. I cannot tell you how many times I had a pilot write something up that was not a big deal to him/her and said to me "It's no big deal you can just sign it off". Well what might not be a big deal to a pilot might be a major headache for us. I am not saying you do this but every now and then it happens..Also you have what I call the 1 percenters who will do it all the time just like there are the 1 percenters in every work group who like to make life miserable for their co-workers.

Amen to all of that. We have one pilot in particular who is just absolutely out of control. I can't go into some of the stuff he has written up in the past on a public forum, but suffice it to say... I'm gaining gray hairs each day.
 
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tb727
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RE: Which T/R Is The Most Efficient?

Thu Jan 21, 2010 3:07 pm

Ahhh the only thing that sounds better than a JT8D is the sound of a JT8D with clamshells.
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2H4
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RE: Which T/R Is The Most Efficient?

Thu Jan 21, 2010 4:43 pm



Quoting C5LOAD (Thread starter):
I was looking at these images and wondered is there any difference in efficiency or amount of reverse power between the three?

Are you asking about thrust reverser efficiency, or thrust reverser effectiveness?
Intentionally Left Blank
 
c5load
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RE: Which T/R Is The Most Efficient?

Thu Jan 21, 2010 9:17 pm

Quoting 2H4 (Reply 12):
Are you asking about thrust reverser efficiency, or thrust reverser effectiveness?

Effectiveness was the word I was looking for at the time, but couldn't think of it, thank you. So that if you had no brakes for whatever reason, which ones would stop you in a shorter distance?

[Edited 2010-01-21 13:18:36]
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411A
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RE: Which T/R Is The Most Efficient?

Thu Jan 21, 2010 10:05 pm



Quoting C5LOAD (Reply 13):
So that if you had no brakes for whatever reason, which ones would stop you in a shorter distance?

L1011, equipped with RollsRoyce RB.211.524B402 engines....reverse thrust VERY effective.
T/R will back the airplane up on the ramp...have done it several times, when a pushback tug was not available.
-22B powered aircraft, also possible.

However, use absolute caution...much FOD is likely, if the ramp in not clean.
 
bond007
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RE: Which T/R Is The Most Efficient?

Fri Jan 22, 2010 2:40 am



Quoting C5LOAD (Reply 13):
Effectiveness was the word I was looking for at the time, but couldn't think of it, thank you. So that if you had no brakes for whatever reason, which ones would stop you in a shorter distance?

Well, none of them are that effective, even the most 'efficient' types. They are most effective on contaminated runways and less effective at slower speeds.

I'd be interested if there are any incidents where an aircraft has landed successfully without coming off the end, using thrust reversers only.

Jimbo
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DashTrash
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RE: Which T/R Is The Most Efficient?

Fri Jan 22, 2010 5:45 am

I can tell you this about clamshells. On the Citation X, when we open the buckets, the airplanes immediately starts decelerating. Those things are huge back there and the drag from them is like opening a small parachute. Start spooling up and the thing will put you into the shoulder harness.

They work so well I usually pop them, get 6 lights, then pull the levers to the stops. As soon as I hear them spool about halfway up, I go back to idle. That quick and you are at 65 kts where you have to be at idle anyway.
 
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aerdingus
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RE: Which T/R Is The Most Efficient?

Fri Jan 22, 2010 3:52 pm



Quoting DashTrash (Reply 16):
They work so well I usually pop them, get 6 lights

Sorry, what do these lights signify?

Cheers.
A306 A313 A319 A320 A321 A333 A346 A359 ATR42 ATR72 B734 B737 B738 B744 B772 B789 C152 MD80 RJ85 S340
 
BMI727
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RE: Which T/R Is The Most Efficient?

Fri Jan 22, 2010 4:14 pm



Quoting Tdscanuck (Reply 3):
Clamshells are the worst for maintenance though...

Not to mention the danger of hot gas ingestion. Incidentally, I was having a similar conversation with my uncle yesterday and he said that he had studied adding thrust reversers to the F-15, but it wouldn't have been worth it.

Quoting AA737-823 (Reply 4):
When this happens, there's no heat (in the bypass duct) to keep things warm, and you soon find you've not only got a reverser that is stuck deployed, but it is now also FROZEN deployed.

I've never heard that one before, but it can't be much fun to fix.
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slimshady
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RE: Which T/R Is The Most Efficient?

Fri Jan 22, 2010 9:17 pm

https://www.airliners.net/photo/USA--...d=66e663306eb446a8c5a78db7008319d6

Both bypass and core have reversers. Sorry, dont know how to imbedd photos..

[Edited 2010-01-22 13:19:09]
 
DashTrash
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RE: Which T/R Is The Most Efficient?

Sat Jan 23, 2010 3:10 am



Quoting Aerdingus (Reply 17):
Sorry, what do these lights signify?

Cheers.

Arm, unlock, and deploy lights. Arm means one latch is unlocked, unlock is two latches, and deploy means all four latches are open. Each reverser has that set of three lights.

Different airplanes indicate in different means. This is how Cessna did it. The Sabreliner had arm and deploy lights (I think).
 
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aerdingus
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RE: Which T/R Is The Most Efficient?

Sun Jan 24, 2010 2:21 pm



Quoting DashTrash (Reply 20):
Arm, unlock, and deploy lights. Arm means one latch is unlocked, unlock is two latches, and deploy means all four latches are open. Each reverser has that set of three lights.

Thanks
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ex52tech
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RE: Which T/R Is The Most Efficient?

Wed Jan 27, 2010 7:27 am



Quoting Tb727 (Reply 11):
Ahhh the only thing that sounds better than a JT8D is the sound of a JT8D with clamshells.

Without the hushkit please. Not to stomp on your nostalgic moment by any means, but a JT3C in water, without the organ pipes in the exhaust was a sound like no other. The KC135As were soooo loud.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
ex52tech
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RE: Which T/R Is The Most Efficient?

Thu Jan 28, 2010 2:24 pm



Quoting AA737-823 (Reply 4):
Curiously, the airline I worked for originally had core-stream reversers fitted, but had since removed them.
That begs the question: which is more effective, a clamshell, or a dual-stream translating reverser?

The dual stream was not effective enough on the high bypass JT9s, and CF6 to justify it's continued use. I have no experience with the turbine reverser on the L1011, but would venture to guess they were similar to the JT9/ CF6 in effectiveness.

They were maintenance hogs, heat, vibration, and soot were enemies of this system.

They were not effective enough to justify their continued use. Even after they were de-activated the translating tailpipes on the CF6's were known to occasionally deploy in flight and then depart, due to the lack of jackscrews to restrict their range of travel. Essentially they were bolted shut, and then forgotten. The bolts that held them shut would wear in the holes, from vibration, expansion and contraction due to engine operation. The bolts would wear down, break off, the translating portion of the tailpipe would move aft, then keep right on going, sometimes taking the center body plug (cone) with it. The dedicated tail pipe solved this problem, but some operators were slow to spend the money on them.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
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747classic
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RE: Which T/R Is The Most Efficient?

Thu Jan 28, 2010 3:09 pm



Quoting Ex52tech (Reply 23):
The dual stream was not effective enough on the high bypass JT9s, and CF6 to justify it's continued use.



The problem was not the effectiveness of the dual (core and fan) reverser on the CF6 and JT9D engines. The combined reverser was very effective.
The problem was the high failure rate (very Low MTBF) of the core reverser on both engines, producing long delays and high maintenance costs. These costs were not offset by the reduced maintenance costs of the (steel) brakes.

After the deletion of the core (we called it : turbine)reverser the effectiveness was actually halved.
If you select reverse only the fan thrust is partly reversed (eff . approx.50 %), the core engines is delivering full FWD thrust.
Operating a twin over the ocean, you're always one engine failure from a total emergency.

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