Author Topic: RAT query  (Read 11327 times)

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Offline nickwilcock

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RAT query
« on: January 20, 2011, 11:33:50 PM »
A query for the eletrickery chaps.

If the RAT is dropped in flight, does it automatically connect to the Synch Busbar, or is it selected manually after the volts and frequency are first checked?

Once the RAT is on the Synch Busbar, I know it can only then be deselected by operation of the RAT field isolation switch; this mod. was fitted after the XM600 accident near Spilsby caused by an over-volting RAT.
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Offline Rushy

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Re: RAT query
« Reply #1 on: January 21, 2011, 07:41:10 AM »
Where's the AEO when you need him? BARRY!!!!!!!
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Offline Grumpyjohn

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Re: RAT query
« Reply #2 on: January 21, 2011, 09:15:30 AM »
The Haynes workshop manual doesn't answer this question, but then car workshop manuals don't usually give much operational information. I suppose we need the owner's handbook!
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Offline brains_mt

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Re: RAT query
« Reply #3 on: January 21, 2011, 11:13:26 AM »
You just need a bigger trap for a rat!!!!! :lol:  ;)
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Offline Zero One

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Re: RAT query
« Reply #4 on: January 21, 2011, 12:24:05 PM »
I'll check my AP101B-1902-1B- Cover 1-Sect.6 this afternoon
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Offline Oberon

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Re: RAT query
« Reply #5 on: January 21, 2011, 01:46:15 PM »
Quote from: "nickwilcock"
A query for the eletrickery chaps.

If the RAT is dropped in flight, does it automatically connect to the Synch Busbar, or is it selected manually after the volts and frequency are first checked?

Once the RAT is on the Synch Busbar, I know it can only then be deselected by operation of the RAT field isolation switch; this mod. was fitted after the XM600 accident near Spilsby caused by an over-volting RAT.


The RAT breaker closes automatically if:
1.  The RAT output is above 180 volts.
2.  There is no supply on the sync busbar.
3.  Number 2 "A" breaker is tripped.




Oberon
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Offline Zero One

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Re: RAT query
« Reply #6 on: January 21, 2011, 03:28:56 PM »
To expand sleightly on Oberons' answer.....

Main Alternator Failure

Assuming failure of all four main alternators above 40,000 ft, the pilot deploys the RAT by pulling the handle top centre main console.

Two micro-switches operate and performs the following functions..

1] Excites the RAT alternator field coil, thus making the RAT ready to accept loads.

2] Sheds Non-Essential Loads, and prepares the AAPP for a Cartridge Start for use under 30,000ft

Voltage & Frequency Check

They are checked by pressing  RAT Test button on panel 10P, this connects the RAT output to the SYNC Bar Volts/Frequency meters, once checked OK the output is now fed, under the control of  the Sync Voltage Pick-up Unit,[VPU]  to the RAT Circuit Breaker which makes and supplies RAT output to the SYNC Bar

Reestablishment of No.2 Main Alternator

Reestablishment of No.2 Main Alternator output to line, the RAT will automatically be TRIPPED and replaced by No.2 Alternator.

Should it be No.s 1, 3, or 4 Main Alternator that comes back on line, the RAT must be TRIPPED by using the extra supplies trip pushbutton on panel 10P  this will trip the RAT  Circuit Breaker and switch the selected alternator onto the Synchronizing  Bus- Bar.


 :)
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Offline nickwilcock

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Re: RAT query
« Reply #7 on: January 21, 2011, 03:52:14 PM »
Thanks for the gen.

OK, during a RAT/AAPP drill, presumably there is another alternator already on the Synch Busbar when the RAT is dropped?

Then the RAT volts/freq are checked before it is connected to the Synch Busbar?  

I can't remember the sequence of actions in a normal practice RAT/AAPP drill; the question is basically if whether it is possible to detect an overvolting RAT before connecting it to the aircraft AC system.  If the overvolting is detected, until the RAT field isolation switch mod. was fitted, would the RAT still power something, even just the RAT circuit breaker?
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Offline Zero One

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Re: RAT query
« Reply #8 on: January 21, 2011, 04:05:38 PM »
Quote from: "nickwilcock"
Thanks for the gen.

OK, during a RAT/AAPP drill, presumably there is another alternator already on the Synch Busbar when the RAT is dropped??

Normally No.2 would sit on the SYNC Bar, during a drill, presumably, the No.2  "S" Breaker would be tripped disconnecting it from the SYNC Bar onto it's own loads only


?
Quote

Then the RAT volts/freq are checked before it is connected to the Synch Busbar?  
?

Have to read my book again but would assume ( I know never ASSUME it makes an ASS out of U and ME) that that is part of the VPUs function??

?
Quote

I can't remember the sequence of actions in a normal practice RAT/AAPP drill; the question is basically if whether it is possible to detect an overvolting RAT before connecting it to the aircraft AC system.  If the overvolting is detected, until the RAT field isolation switch mod. was fitted, would the RAT still power something, even just the RAT circuit breaker?

Pass, never haveing been involved with a RAT/AAPP drill... At Bruntingthorpe, RAT was a little redundant as we never got to 40,000ft :lol:  :lol: .... will try to find out

 :)
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Offline Zero One

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Re: RAT query
« Reply #9 on: January 21, 2011, 07:24:59 PM »
Just read my FRCs...

card 20(AL11)... Electrical Limitations
RAT
1.. Voltage..............................115+/- 5v (one phase to earth)
2.. frequency...........................400+/-20Hz
3.. Max loading.........................17kw
4.. Altitude..............................60,000 to 20,000ft
5.. Airspeed.............................Above 0.85m/250knots
6.. Max duration........................10 mins above 50,000[off load] or 30,000[on load].. Land within 90min in training case

Card21(AL21)...RAT DRILL..
1.. Initial checks[card 20R].......................Complete)
2.. RAT Test Button...............................Press
3.. RAT
            (a). Order Release
            (b). check NE loads, indicate.. Shed
            (c).  check output within limits[card 20] within 2secs

4.. Airspeed.........................................Ajust in descent to keep RAT within limits
5..  NE supplies.....................................Crew confirm off[card 26]
6..  Alternator Panel
      (a) No.2 on SYNC, 1,3,4 isolated
      (b) RAT within limits
      (c)  No.2 switch off
      (d)  RATon SYNC Bar within limits
7.. RAT Output.......................................Ajust speed to keep RAT in limits


So it looks to me as though the action of switching off No.2 Alternator is the control.... for switching the RAT onto the Sync Bar...

So regarding the overvolting question this would probably happen (card 21 3c above) before No.2 Alternator is switched off....any ex-AEOs out there to confirm or correct?

I'll get back to my Nimrod APs now... :D

Have I got too much time on my hands??? :twisted:

Opinions please?


 :)
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Offline nickwilcock

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Re: RAT query
« Reply #10 on: January 21, 2011, 08:45:53 PM »
Many thanks for all that research - it's pretty well what I'd (vaguely) remembered from 35 years ago.

Not a well-written drill - it doesn't tell the AEO what to do if the RAT is outside limits (although most would probably know).  There should be something stating "If RAT outside limits, DO NOT attempt to connect to SYNC bar.  Descend to FL300 or below and land as soon as practicable" or similar.  I suspect most AEO's FRCs would be full of pencil notes though!

But usually we did the RAT/AAPP drill at the end of a high-level borex, then landed.
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Offline StAthan lecky

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Re: RAT query
« Reply #11 on: January 22, 2011, 09:31:52 AM »
I'll get back to my Nimrod APs now...  

Have I got too much time on my hands???  

Opinions please?


Get yourself a Harrier to play with,that should keep you busy

 :lol:  :lol:  :lol:  :lol:  :lol:

Mike
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Offline Zero One

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Re: RAT query
« Reply #12 on: January 22, 2011, 09:47:46 AM »
Quote from: "StAthan lecky"
I'll get back to my Nimrod APs now...  

Have I got too much time on my hands???  

Opinions please?

Get yourself a Harrier to play with,that should keep you busy

 :lol:  :lol:  :lol:  :lol:  :lol:

Mike

Fine get me the money to buy one and I'll look after it..... I'm the next in line for one of my own...or a Dominie will do ... ;)  :twisted:
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Offline nickwilcock

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Re: RAT query
« Reply #13 on: January 22, 2011, 05:58:03 PM »
Or perhaps some VCTenderness??

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Offline za150

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Re: RAT query
« Reply #14 on: January 23, 2011, 12:40:24 PM »
Quote from: "nickwilcock"
Or perhaps some VCTenderness??

Yes Please, ZA150 would be just fine.......
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