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HAWK21M
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B752 RAT Safety Cage

Mon May 29, 2006 10:08 pm

How practically is the B752 RAT safety cage used during RAT ground checks.
Any Pics.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
A/c train
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RE: B752 RAT Safety Cage

Wed May 31, 2006 6:06 am

Not too sure what answer your looking for here Mel, its just a round cage which sits around the rat, it comes in 2 halves and you bolt the two halves together when there in position either side, can be a bit of a fiddle. Then you do the backdrive, theres a panel you have to take off in the back of the r/h main gear bay, there is a switch there to stow the RAT with HYDs on and in that area there is the wirelocked rocker arm which you actually use to backdrive the RAT, been over a year since I did one though!
 
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HAWK21M
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RE: B752 RAT Safety Cage

Wed May 31, 2006 10:47 pm

Thanks A/c train.I'm aware of the RAT Checkout module & the Ground control module.
What I was curious was that Is the RAT cage attached to the Aircraft or touching it at any time.Or just on the Ground.
Have not done a RAT check yet so not sure & we dont have a cage as yet.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
AvionicMech
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RE: B752 RAT Safety Cage

Thu Jun 01, 2006 4:57 am

Mel,

The cage that we use is not attached to the aircraft at all or even touching it. It is a very basic bit of kit, it is only 2 U shape cages which bolt together to completely surround the RAT but I have seen more often than not people doing back drives without a cage.
 
broke
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RE: B752 RAT Safety Cage

Fri Jun 02, 2006 1:30 am

RAT safety cages are used on every airplane that I know of that has a RAT. There have been cases during a ground test of a RAT, where it had shed one of its blades. You don't want to be in the plane of the RAT rotor when it loses a blade during a ground test, especially if the unit is not caged. It will definitely ruin your day.
 
OldAeroGuy
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RE: B752 RAT Safety Cage

Fri Jun 02, 2006 4:00 am

Given the energy in a RAT blade at full RPM, I suspect that the cage is there to keep people from walking into it although the you'd think that the noise alone would be sufficient.

The cages I've seen probably wouldn't stop a RAT blade released at full RPM.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
saintsman
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RE: B752 RAT Safety Cage

Fri Jun 02, 2006 3:54 pm

I'm curious here. Why would you test a RAT on an aircraft? isn't that a bay job?

The only test I have seen done is a drop test and that was done with people holding onto it to stop it banging against the stops.
 
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HAWK21M
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RE: B752 RAT Safety Cage

Fri Jun 02, 2006 6:30 pm

Quoting Saintsman (Reply 6):
Why would you test a RAT on an aircraft

To check if it would deploy under the Given conditions & thats its running at the Correct RPM to supply Hyd pr at the required level.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
saintsman
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RE: B752 RAT Safety Cage

Fri Jun 02, 2006 6:46 pm

I don't know anything about the B752. Does it just supply just hydraulics or electric as well?

Given that the RAT is air driven, how do you ensure that it is running at the correct RPM?
 
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HAWK21M
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RE: B752 RAT Safety Cage

Fri Jun 02, 2006 6:55 pm

Quoting Saintsman (Reply 8):



I don't know anything about the B752. Does it just supply just hydraulics or electric as well

On the B752 only Center system Hydraulics.
For Electrics there is an Optional HMG [Hydraulic Mechanical Generator] Available on some Aircraft.Mainly those requiring ETOPS certification.

Quoting Saintsman (Reply 8):
Given that the RAT is air driven, how do you ensure that it is running at the correct RPM

Indicator lights on Test Module Red/Green for Speed generated in Backdrive mode.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 1:10 am

Hey Fellas, this is my very first post! I've been reading and learning on A.net for a while, and thought I would join in the conversation.

Yes, the RAT is backdriven in the hangar, and can occasionally throw a blade from the turbine. I'm not sure if the cage would contain the blade, because the turbine spins at approx. 12K RPM. As Broke said, it would most definitely ruin your day.

We test these units, as well as the RATs for the B767, A300-600, A320, A300B2/B4, L1011 and several others in our wind tunnel. We've been pretty lucky that a blade hasn't been thrown, but we've had stuff impact them during the test. Pretty ugly.
"The only people for me are the mad ones...." Jack Kerouac
 
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HAWK21M
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 2:22 am

Quoting EasternSon (Reply 10):
We test these units, as well as the RATs for the B767, A300-600, A320, A300B2/B4, L1011 and several others in our wind tunnel.

Any Pic of this Tunnel.BTW Welcome.  Smile
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 2:27 am

Thanks for the welcome, HAWK21M, but unfortunately, the wind tunnel and its design are proprietary information. There are lots of people in the industry who'd like to know what it looks like!

All I can tell you is it's very large, very loud, very expensive, and can blow like, well, the wind.

I'll check to see if I can upload a movie of a RAT in the tunnel, but my boss would probably say no.
"The only people for me are the mad ones...." Jack Kerouac
 
EasternSon
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 2:29 am

BTW, I misspoke before, the RAT spins at approx. 6.5K, not 12K RPM.

I got it confused with some of the smaller Air Driven Generators that we work on, like the CRJ and Challenger, which spin much faster.
"The only people for me are the mad ones...." Jack Kerouac
 
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HAWK21M
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 2:34 am



Quoting EasternSon (Reply 12):
unfortunately, the wind tunnel and its design are proprietary information. The

Understandable.

I watched the Deployment of an A320 RAT in Slow motion & it was Fast.
Comparably the B752 RAT was slower.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 2:51 am

Big version: Width: 1166 Height: 1535 File size: 351kb


Sorry, I'm not allowed to upload the video, but here's a pic of one hanging in the test rig.

Yeah, those things really snap down hard. I'm not sure if we do a drop down test into the airstream, but it wouldn't surprise me if we did.

The Boeing RATs are tested at slower wind speeds, I believe, as compared to the Airbus RATs, but the deployment speeds are similar.

How did you get your hands on the Sundstrand flyer? Do you work for them?
"The only people for me are the mad ones...." Jack Kerouac
 
OldAeroGuy
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 9:54 am

Quoting EasternSon (Reply 15):
The Boeing RATs are tested at slower wind speeds, I believe, as compared to the Airbus RATs, but the deployment speeds are similar.

All RATs have operate at airplane speeds up to Vmo/Mmo. Check these speeds to see what a given RAT's capabilities are.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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HAWK21M
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RE: B752 RAT Safety Cage

Sat Jun 03, 2006 8:01 pm

Quoting EasternSon (Reply 15):
How did you get your hands on the Sundstrand flyer? Do you work for them

No.But our B752s have them.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Mon Jun 05, 2006 9:46 pm

Mel,

Just out of curiosity, have you heard anything regarding the 20 yr. overhaul requirement?

It was rumored that Boeing and the RAT manufacturer were pushing for a mandatory removal, much like those instituted for many of the Airbus RATs. The OEM even went as far as to write the requirement into the CMM.

Any buzz in your maintenance department regarding a possible AD?

Thanks,

Paul
"The only people for me are the mad ones...." Jack Kerouac
 
EasternSon
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RE: B752 RAT Safety Cage

Mon Jun 05, 2006 9:57 pm

"All RATs have operate at airplane speeds up to Vmo/Mmo. Check these speeds to see what a given RAT's capabilities are."

Forgive me, but I have no experience with the RAT when it's on the aircraft, only being tested in the tunnel. If you would, please explain what Vmo/Mmo are?

I just checked the test procedures for the Boeing vs. the Airbus RATs, and the B757 RAT is blown at significantly lower speed than the A310 RAT. Would this have to do with the glide speed of the respective aircraft in a total power loss?
"The only people for me are the mad ones...." Jack Kerouac
 
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HAWK21M
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RE: B752 RAT Safety Cage

Mon Jun 05, 2006 10:12 pm

Quoting EasternSon (Reply 19):
please explain what Vmo/Mmo are

Maximum Operating Velocity.
Maximum Operating Mach.

Quoting EasternSon (Reply 18):
Any buzz in your maintenance department regarding a possible AD

Not yet.
20yrs for a RAT Replacement is a long time.What is the Reason,as RATs are seldom used.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Mon Jun 05, 2006 10:47 pm

The reason for the potential AD is corrosion.

There have been several ADs issued for RATs in the past years. Beginning with the L1011 RAT, then the A300B2/B4, and on to the A300-600/A310 RATs. The next issued will most likely be for the A320.

However, several of our customers (large US operators) have told us that the OEM and Boeing have both approached them to gather information regarding removals and the subsequent findings. While the Boeing RATs do not seem to corrode as easily as the Airbus, the OEM is still pushing for an AD to be written. They salivate when they think about a mandatory removal of a component used on thousands of aircraft worldwide, especially when they get to charge $100K for each overhaul.
"The only people for me are the mad ones...." Jack Kerouac
 
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HAWK21M
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RE: B752 RAT Safety Cage

Mon Jun 05, 2006 10:55 pm

Quoting EasternSon (Reply 21):
While the Boeing RATs do not seem to corrode as easily as the Airbus,

Is there a Material Difference.
Where is the Corrosion noticed.
On the Arm.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Mon Jun 05, 2006 11:14 pm

Big version: Width: 2576 Height: 1952 File size: 1295kb


No, there is no material difference. We believe that the corrosion is accelerated by where and how the RAT is stowed on the Airbus vs. Boeing. I have to plead ignorance on the Airbus, but you and I both know where the RAT is on a Boeing. Maybe better seals to the doors, less condensation?

I've attached a picture of one of the main areas of the strut arm that has the most corrosion. This is the top of the strut, where the main post connects the RAT to the aircraft. Corrosion is also noted where the turbine mounts to the strut. The worst corrosion, however, is always found in the hydraulic pump sub-assembly.

The corrosion, plus the fact that undue pressure is put on the pistons and plates in the pump during backdrive, usually causes failures.

How many have you tested? Any failures? Do you remove the entire RAT, or just the turbine and the pump?
"The only people for me are the mad ones...." Jack Kerouac
 
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HAWK21M
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RE: B752 RAT Safety Cage

Tue Jun 06, 2006 12:38 am

Quoting EasternSon (Reply 23):
How many have you tested? Any failures? Do you remove the entire RAT, or just the turbine and the pump

Our B752s have just started flying last month.Not much Experience there.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
EasternSon
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RE: B752 RAT Safety Cage

Tue Jun 06, 2006 1:05 am

Good luck with the B757s. They're great aircraft.

Please let me know if you ever do drop a RAT in the hangar for testing. I'd be interested to hear what your thoughts are and any problems you encounter.

Though I may not be able to help with any answers, I've got roughly 15 RAT mechanics at my disposal who I could pass any questions along to.

BTW, thanks for making my entrance into a.net a painless one. Look forward to posting again.

Kind Regards,

Paul
"The only people for me are the mad ones...." Jack Kerouac
 
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HAWK21M
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RE: B752 RAT Safety Cage

Tue Jun 06, 2006 1:37 am

Quoting EasternSon (Reply 25):
Please let me know if you ever do drop a RAT in the hangar for testing. I'd be interested to hear what your thoughts are and any problems you encounter.

Will Def use your Experience If the need arises.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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