R.A.T. Redundant operating systems?

[DanAir1-11]

Can anyone enlighten me on the operation of RAT's.
What I am interested in ascertaining is if there are redundancies built in to the operating system. Ie how is the RAT released and if the system controlling the release fails, is there a redundancy?

I am not even sure if all systems operate in the same manner, but any info from a wide range of equipment will be greatly appreciated.

Thank-you.

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[None]

The automatic deployment on the 757/767 occurs with dual engine failure. If the auto deployment fails, manual deployment can be accomplished. A green light on the manual deployment button lets you know it is providing hydraulic pressure for the prescribed flight controls, the only items powered by teh 757/767 RAT.

Electrical systems may be powered on other types.

[HotDog]

L1011 RAT supplied Hyd.Sys. B and C. Two ATM control switches on FE's upper panel marked OFF-AUTO-ON-OVSP TEST positions. Normal selection AUTO. In air conditions for AUTO RAT deploy: >100KTS, <5500RPM all engines.

[Max Angle]

On the A320 family the RAT deploys automatically in the event of loss of both main AC buses. It powers the blue hydraulic system which is used to power a small generator to provide essential electrics. Can be deployed and coupled manually if required.

[QAVION]

The 767 Manual and Auto RAT deployment system uses different relays and limit switches. The same "extend" electric motor is used in both cases however.

Hot Battery Bus only is required for Manual deploy. Battery and Hot Battery Bus is required for Auto Deploy.

I assume the BAC111 has something similar? (Not sure if you're asking about RATs in general... or BAC11 RATs?).

Regards.
Q.

[allthatglitters]

The BAC 1-11 did not require a RAT as flying controls had full manual reversion, Elecs supplied by battery and clock work instruments.
The L1011 Rat did not power the B and C systems. It supplyed B System only. Rat operation by Auto function with manual override.
"Two ATM control switches on FE's upper panel marked OFF-AUTO-ON-OVSP TEST positions. Normal selection AUTO"
These were Air Turbine Motors, which were powered from the pneumatic systems. One powered B sytem and the powered C system

[HotDog]

allthatglitters, of course you are correct. I got confused, the RAT manual deploy switchlight is positioned below and slightly to the right of the B SYS. ATM control switch. It's a long time since I operated the Tristar. Cheers, HD.

[Compass Call]

allthatglitters

The BAC 1-11 had an APU supplying electrical power & aircon only. I do not recall the 1-11 having manual reversion at all. The ailerons were manually 'flown' by a cable operated tab (no hydraulics at all) and the rudder & elevators were hydraulic powered. Emergency elevator was powered by a DC operated trim tab. There was no emergency control over the rudder. Emergency flaps could be selected by a DC pump (down selection only). If the APU could supply AC power, then hydraulics was not a problem as there were two AC hydraulic pumps, one for each system, assuming each system was intact!

But I stand ready to be corrected.

CC

[fixa24]

some variants of the b767 also have HMG's (hydralic motor generators) which provide emergency power to the bus. its a small generator in the lh wheel well driven by hydraulic pressure , doesnt have to be only when the rat deploys either...

[mono]

The RAT on the 767 does not supply hydraulics for the HMG. If the RAT has deployed the hydraulic fluid is routed via an isolation check valve which ensures that the output is used for primary flight controls only.

This will be:-

i/b ailerons
spoilers 3,4.,8,9,10
elevators
rudder

It will also supply the centre a/p servos, left Yaw damper primary stab trim and elevator feel.

If the HMG was also supplied it would over load the RAT and not enough power would be available for flight controls.

Conditions for deployment are a/c in the air, 80+kts airspeed and both engines less than 50% N3

There is also a priority valve in the circuit of the A320/1 which reduces hydraulic output to the emergency generator and slats if hydraulic pressure is low or demand is high. Not sure what effect this would have if the electrical power was lost due to a dual engine failure. Perhaps a question for the next sim check?!!

Airbus deployment conditions a/c in the air, 100+kts airspeed and both main ac busses failed.

Both a/c types are able to deploy the RAT manually from the hot batt bus

[DanAir1-11]

"There was no emergency control over the rudder"

I am fairly sure that the rudder can be moved manually due to the mechanical linkage of the servo valve operating rods. A small degree of lost movement will occur prior to the rods reaching E.O.T. and reacting against the PCU

Elevators can definitely be manually operated and have geared tabs and mare mass balanced to assist.

Regards