Hydraulics provided by the APU ?

Do I have my full hydraulics with APU on? If no, what do I lose? The manual says the APU gets a hydraulic pump running but doesn't give me more precision as far as I know.

I noted that the maple flag amplified checklist tells me to switch to manual reversion if my engines are out even if I have the APU running. So it would suggest that the hydraulics provided by the APU aren't sufficient to make proper use of the flight controls. Is it correct? Thanks for the help!

Do I have my full hydraulics with APU on? If no, what do I lose? The manual says the APU gets a hydraulic pump running but doesn't give me more precision as far as I know.

 

I noted that the maple flag amplified checklist tells me to switch to manual reversion if my engines are out even if I have the APU running. So it would suggest that the hydraulics provided by the APU aren't sufficient to make proper use of the flight controls. Is it correct? Thanks for the help!

AFAIK, the APU operates a 10 gallons per minute (GPM) pump, compare that to the two main pumps that are 43gpm. Also the APU can only power one of the systems at a time and can not be use in the air.

Auxiliary Power Unit Driven Hydraulic System

The APU driven hydraulic system provides hydraulic pressure to the left or right

hydraulic system for limited ground maintenance. The APU driven hydraulic system is

for ground use only and cannot be selected in flight. The APU hydraulic pump operates

whenever the APU is operating. The pump has a rated capacity of 3,000 psi at 10 gpm.

Pressure from the pump is directed to the left or right hydraulic system by use of manual

transfer valves. The electrical portion of the APU driven hydraulic system is supplied by

the right Direct Current (DC) system bus through the EJCTR AIR/CAN SEAL circuit

breaker. The APU driven hydraulic system contains an electrical fan mounted on a

cooler, which cools the hydraulic fluid when the manual transfer handle is stowed. The

cooling fan is powered by the APU generator. APU operation is limited to 5 minutes

when the APU generator switch is not set to PWR.

APU can be used to drive the hydraulic systems, but that's only for maintenance.

The APU can only operate one system at a time and has to be manually selected (left or right) by a handle. The handle can only be accessed through a panel near the APU.

Very good information. Thanks a lot guys! :)

I also have a question regarding the APU. In the emergency checklist for a failed AC Generator, it says that if the generator doesn't come back online after three reset attempts, then you should start the APU below 15000 MSL and engage the APU Generator once the APU RPM has stabilized.

If the APU can only power one system at a time, and the system can mostly only be set on the ground, what's the logic in turning it on in the first place?

I also have a question regarding the APU. In the emergency checklist for a failed AC Generator, it says that if the generator doesn't come back online after three reset attempts, then you should start the APU below 15000 MSL and engage the APU Generator once the APU RPM has stabilized.

 

If the APU can only power one system at a time, and the system can mostly only be set on the ground, what's the logic in turning it on in the first place?

Two different systems. The Hydraulics can only be used on the ground and it can only power one hydraulics system at a time. The Generator is a different story.

Emergency Power System

The emergency power system consists of the battery and inverter. The battery supplies

power to the DC essential bus in the absence of converter output. The inverter is

powered by the DC essential bus, and in turn supplies 115 VAC, three-phase power to the

AC essential bus, AC auxiliary essential buses, and 26 VAC instrument transformer bus

in the event of total loss of all AC generator outputs. The emergency power system also

supplies battery power for Auxiliary Power Unit (APU) starting when generator or

external power is not available. When the BATTERY switch on the ELEC PWR control

panel is set to OFF, and the external BATTERY switch is set to ON, the battery supplies

power directly to the battery bus. When the BATTERY switch on the ELEC PWR

control panel is set to PWR battery power is applied to the DC essential bus and APU

start relay

[ATTACH]170462[/ATTACH]

I understand the generators fairly well, but what I meant was; if the APU can power only one hydraulic system at a time, and is only useful on the ground, then why turn it on in the event of a generator failure? It seems to me like the APU would be useless in the air.

I understand the generators fairly well, but what I meant was; if the APU can power only one hydraulic system at a time, and is only useful on the ground, then why turn it on in the event of a generator failure? It seems to me like the APU would be useless in the air.

??? The emergency procedure is for electrical (generator) failure. Not sure why you’re confusing hydraulic pump and electrical generator.

Ok, I think I see where I'm getting confused. The APU can provide electrical power in the air in the event of an emergency, but it CANNOT provide full hydraulics, since that's only provided on the ground, one system at a time.

If the above is correct, then my confusion was that the ONLY thing the APU could do in the air was provide hydraulics to one system at a time, predetermined by a lever set on the ground. The fact that it also provides electrical power in air somehow blew right over my head.

In the flight configuration the APU provides no hydraulic power at all. It is either not permissible or possible to configure the APU for hydraulic power except when on the ground.

APU is good for AC and bleed air.

MRFCS selection on dual engine failure is a distinct different between the real and sim airplane with the real airplane not retaining hydraulic pressure very well with the engines off (few seconds). Sim airplane you can put on an air show and the PFCS won't drain off enough of the latent pressure to ever matter. You'll even get some pressure back if it drops just be the engines windmilling (inaccurate)!

MRFCS back in beta of the sim was also pig. The model was "joystick input is stick movement" so if you put the stick 1% left it would keep going left until the stop unless some limit was reached. It was very awkward and counter intuitive "for the sake of being hard because MRFCS should be hard" they said. They've since changed it to matched position which is much easier.

Manual Reversion was so bad, and windmilling engines produced to much hydraulic pressure (Big cough cough) that I haven’t tried Manual Reversion in forever.

Need to test the windmilling engine hydraulics issue and man rev to see how it is now.

Need to test the windmilling engine hydraulics issue and man rev to see how it is now.

I'm pretty sure windmilling engines still provide almost full hydraulic power so that engine failure hardly ever triggers hydro failure.

As for manual reversion, I know too little about how it works and feels in the real aircraft. I think its DCS implementation hasn't changed much in recent years, though.

Need to test the windmilling engine hydraulics issue and man rev to see how it is now.

You will see, when in manual reversion mode the stick vibrates like crazy. It's a pretty weird bug and quite a big immersion killer. The rudder pedals do vibrate as well but only when actuated if I remember correctly.

Didn't notice the vibration the first time. It quits below ~145 knots (speed varies) or so. It must be the check against pilot strength. Yeah that's weird.

Fun story the pitch trim in MRFCS is reversed. Nose up makes nose down :P Both primary and backup trim hats. We don't notice normally since the PFCS pitch trim simply repositions the artificial feel device (stick neutral position moves). The tabs are only moved (geared) such that transition to MRFCS won't be too violent.

I wonder if the pilot has enough strength to sheer the elevator interconnect in MRFCS.

MRFCS seems perfectly flyable with flaps out which should not be the case. The flaps emergency retract is there almost solely for that reason, not that the flaps retract does much.

AIL TAB caution lights are not coming on. Roll authority seems way too good.

Remember that whole "joystick input continues to drive elevator when not centered." That's still there. Sit on the ground MRFCS and input a tiny aft stick. It'll run the elevator to full stop unless you recenter.

I think there's something wrong with the systems dependency. I schedule a L/R hydraulics failure by the ME and it lists it in the action log but hyd continues unaffected.