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View Full Version : How much electrical/hydraulic power will the Ram Air Turbine Supply (a320)?


WhySoTough
17th Aug 2012, 05:22
Just randomly thinking of this earlier today.

Not sure where to find this answer.
On an unlucky day if both engines failed, and apu was inoperative.
You've lost all electrical and hydraulic supply.
How much electrical and hydraulic supply will the ram air turbine give.
Will the RAT pressurize the blue hydraulic system to it's full potential?

On another scenario, both engines fail but apu was operative, are you now in a much much better sitation than having it inoperative, or is it just as bac since hydraulics are still not working.

I know the questions sound stupid, but I'm a little curious, also a little confused.

Thanks guys.

BlackFly78
17th Aug 2012, 06:00
The rat will (of course) supply the complete blue system with 70l/min (the elec pump only have 25l/min, the EDPs 140l/min) and will also supply electrical power via CSM/G

If the APU is running, it is your lucky day ;) The APU will supply electrical power to every System/Bus, pneumatic to als pneumatic systems and hydraulic is working via both pumps (green and blue, yellow ist powered with the PDU from Green). This config is therefore nearly normal flying like with a glider ;)

IFixPlanes
17th Aug 2012, 06:25
... How much electrical and hydraulic supply will the ram air turbine give. ...CSM/G. . . . . . . . . . . 5 kVA
IDG . . . . . . . . . . . . 90 kVA

RAT Hydraulic Pump Output
Rated Flow Capacity . . . . . . . . . 18.5 gpm
Discharge Pressure . . . . . . . . . . 2,320 psi

EDP Output
Rated Flow Capacity . . . . . . . . . 37.5 gpm (minimum)
Discharge Pressure . . . . . . . . . . 3,000 psi

glum
17th Aug 2012, 09:09
Providing your APU can provide bleed air, I suggest you are in a much better position as you can maintain pressurization, and therefore don't have to descend quite so quickly.

It should also mean you can try to re-start the main engines. Without bleed air, you'd have to rely on windmilling, and this may not be possible in an A320.

I don't know about A320 specifically, but I suspect the APU output is capable of provoiding full electrical power and hydraulics whereas the RAT will only give you enough for emergency systems.

TURIN
17th Aug 2012, 10:55
If APU gen is operative then all Hydraulic systems can be powered but as the Green system will be being pressurised through the PTU from Yellow (electric) pump there will be limited flow/pressure during heavy use. Blue will be powered by the Blue standby electric pump.

The RAT gives absolute minimum, above a certain speed and with the nose gear up. Turbulence off the nose gear was a problem years ago, I don't know if that has been tackled with increased min speed or modified RAT.

I think. Not having the AMM handy could mean I'm talking utter bowlarks of course. :O

BlackFly78
17th Aug 2012, 13:09
The RAT gives absolute minimum, above a certain speed and with the nose gear up. Turbulence off the nose gear was a problem years ago, I don't know if that has been tackled with increased min speed or modified RAT.

The RAT is modified, visible on the RAT Door. The "old one" is flat and the "modified one" not.

But, the "old one" is working also with NLG down and it is stop working (if i'm remind me correct) with approx 90knots and then you don't really need hydraulic or electrical power. Then you will stop with the brake akku and evac with the emergency light and the slide raft

WhySoTough
17th Aug 2012, 15:17
Thank you guys very much for your responses.
Another confusion.
How exactly do the green and yellow engine driven hydraulic pumps start working with the APU?

vs69
17th Aug 2012, 15:32
Green and Yellow EDP's will not be providing output as a result of the APU running.... HOWEVER..... If you have the APU running and the apu gen is working as it should then the Yellow system can be pressurised by the electric pump and this in turn will cause the Green system to be pressurised by the PTU (Barking dog in the hold) as if a pressure differential is sensed between G+Y one will pressurise the other. (No fluid transfer takes place)

The above scenario assumes the engines aren't running and G+Y edp's are not giving system pressure.

There may be altitude restrictions for apu use so a descent to this height may be necessary, cant remember...

TyroPicard
17th Aug 2012, 20:33
TURIN..
Blue will be powered by the Blue standby electric pump
No such animal .. the BLUE ELEC PUMP will keep running if AC1 power is available from the APU when the engines fail. YELLOW ELEC pump is powered from AC2.

A windmilling engine hydraulic pump will provide a reasonable pressure and flow down to about Green Dot speed, enough for flight controls except flaps/slats.
(Caution....from observation in the simulator).

TURIN
17th Aug 2012, 21:28
Fair point Tyro, I'm used to calling it the standby pump as the override switch (for ground ops) is remote from the main panel. My mistake. :ok:

Of course the Blue electric pump only runs on the ground with an engine running or if in flight. (In Auto mode). :O