Will your hydraulics be available IF..

[z.khalid]

This probably will sound silly for a lot of guys out there.
For example on the Airbus.
The green hydraulics system is pressurized by Engine number 1.

If you lose generator 1, I assume you've lost your green hyd system?

How exactly does the engine 1 pressurize the green hyd system.
Via bleed air?

I am just self studying a lot of things in general.
Thanks in advance. :ok:

[Capt Claret]

Not Airbus endorsed but usually it is a gear driven hydraulic pump, driven from the engine's accessory gearbox.

In the B717 & BAe 146 & DHC8, with which I am familiar, this is the case, and, there is a standby electric driven hydraulic pump as backup.

Modern aircraft are designed to avoid the scenario you cite, whereby a failure of a generator takes out another, non related system.

[dhardesthard]

If you lose the generator on number one engine you have lost electrical power from the electrical generator. Hydraulics have not been affected. The No. 1 engine provides green hydraulic power via an EDP (engine driven pump). It is a mechanical pump which is attached to the gearbox of the engine.

[z.khalid]

Capt Claret,

Thank you for the response.
There are 3 hydraulic pumps in the airbus, and flight controls are spread with more than just one kind, so that if ONE fails, you can still use it with another hyd system.

Do all hydraulic systems have a standby electric driven hydraulic pump?

[z.khalid]

dhardesthard,

Thank you for the response.
So you would lose the hydraulics of that engine IF you had an engine failure or EDP fail?

[Capt Claret]

DH8 (not current since 2001), 2 x AC generators, 2 x DC generators, 2 x Engine driven hydraulic pumps. 1 x standby electric driven Hyd pump.

BAe146 (not current since 2005) 2 x IDG (integrated drive generator), 2 x Engine driven hydraulic pumps, 1 x standby electric driven hyd pump plus 1 x transfer unit, which allowed one hydraulic system to power the other, if required.

B717 (current) 2 x IDG, 2 x Engine driven hydraulic pumps, 1 x electric driven hydraulic pump plus 1 x Transfer pump (similar to transfer unit in BAe146) allowing pressurisation of one hydraulic system by the other.

So you would lose the hydraulics of that engine IF you had an engine failure or EDP fail?

Not in the above three types. An engine failure, or an EDP failure, or both on one engine, would not necessarily render the hydraulic system inoperative. Open TSFR Pump/Unit, and pressurise the HYD system on the side of the failed engine/EDP with the opposite system.

[dhardesthard]

If the engine fails you would lose that SOURCE of electrics and hydraulics and bleed air. However the A/C would still have all its hydraulic, electrical and pneumatic systems powered by their respective back-up sources.

[z.khalid]

dhardesthard,

Thanks again, and a few more questions if you don't mind.
Respective back up sources are the other two systems yes?

Also, if you lost your engine generator only, can that engine still supply bleed air for aircon packs, wing anti ice, etc?

Sorry for asking too much..

[Avionker]

Generator failure will have no effect on bleed air or hydraulics.

A generator failure may trigger automatic load-shedding of non-essential systems, such as IFE and galley power, but all essential systems will continue to work as normal.

[Capt Claret]

Respective back up sources are the other two systems yes?

In most cases yes.

B717,

2 x IDG plus APU IDG, any one can supply whole electrical system requirements.

Aircon packs. One engine can supply air for both, but normally just one pack would be used for pressurisation.

2 x EDP plus STBY HYD Pump. Any one can supply hydraulic power to both HYD systems.

Also, if you lost your engine generator only, can that engine still supply bleed air for aircon packs, wing anti ice, etc?

Failsafe design means the aircraft and it's systems are designed so that one failure, say of an engine generator, won't cause other unrelated systems to fail.

Bleed Air requires electrical inputs for control and monitoring but 1 generator system failing, won't stop this electrical supply, just the source will change, therefore a generator failure won't stop the engine supplying bleed air as required.

[dhardesthard]

On the Airbus you have Green, Blue and Yellow hydraulic systems. The names have noting to do with the colour of the hydraulic fluid. Different manufacturers call them left, right, A, B etc. They all use the same fluid out of the same container. The systems are isolated from each other in that they do not mix. You have engine driven mechanical pumps in each engine. You also have a power transfer unit (PTU). And you also have an electrical pump. Finally you also have a Ram Ram Air Turbine (RAT). The EDPs are self explanatory. The electric pumps are also I believe easy to understand. The PTUs connect two systems mechanically but not chemically. If the normal source (EDP) fails then the PTU from the pressurised remaining system will spin a shaft (for lack of words) that will create hydraulic pressure in the failed system. The RAT is a little turbine(pump) that has a little propeller attached to it that sits folded(props) and concealed in the belly of the A/C somewhere between the two main gear. It is armed to automatically deploy under certain conditions or can be manually deployed by the crew. I have been off the A320 for the last 6 years so my explanations may be a bit inadequate.

[dhardesthard]

Forgot to answer your second question. The hydraulic, electrical and pneumatic sources on each engine are separate and thus the loss of any one or two will not affect the others. The only way that all three would be affected is if the engine fails or the engine goes to a sub(below) idle speed. You will get normal electrics and hydraulics down to idle speed. Pneumatics may be affected at idle speed.

[capt. solipsist]

dhardesthard,

you may have been off the bus for the last 6 yrs but your knowledge is still spot on :ok:

[grounded27]

Do all hydraulic systems have a standby electric driven hydraulic pump?

To simplify things on the A300/A310each motor has 2 EDP's G&Y then G&B, there are transfer pumps from green to yellow and green to blue. Green has 2 standby or electric hyd pumps. If all EDP's died you could still power all 3 systems via the elec pumps on G transfering power to the B&Y. Then the rat.

the engine goes to a sub(below) idle speed

Are you sure about that one? I have observed 3000 psi prior to max motor on start. I do not know how much A/S you would need to keep the n2 spinning fast enough.

[dhardesthard]

Thanks for the kind words capt solipsist. I spent 8 years on the 320/321 so had time to get to know the systems quite well plus I like to meddle with cars, motor bikes and anything mechanical.

[spannersatcx]

It's not mention which type of Airbus, unless I have missed it somewhere.

The 330 has 2 green EDP's 1 on no1 eng 1 on no2 eng, so if you lost No1 eng as asked you would not loose the green system.
A340 also has 2 green system EDP's 1 on no1 eng 1 on no4 eng, so again loosing no1 eng you will not loose the green system.

[dhardesthard]

You are quite right re 3000 psi being achieved prior to idle speed during the start sequence. However sub idle means any rpm below idle including in the area from 0 to 5 or 6 or 7%. I doubt that you would get 3000 psi at those low rpms. My point was that 3000 psi was only guaranteed down to idle speed. Between idle and 0% the pressure would fall from 3000 psi to eventually 0 psi.

[dhardesthard]

I am only familiar with the systems on the A320 family and thus my explanations do not necessarily cover to the other types of Airbus equipment.

[Tu.114]

For the Dash 8-400:

#1 Hydraulic system is powered by #1 engine and/or an electrically driven standby pump.

#2 Hydraulic system is powered by #2 engine and/or a power transfer unit taking power from #1 Hydraulic and pressurising the #2 system. There is also a little pump to pressurise the parking brake reservoir in case it has bled off during longer ground times. Nothing like a little workout during the walkaround - this pump is muscle-driven and also mounted in a position in the R/H wheel well that requires many shorter guys to stand on the wheel or another stand to operate it.

And two oddball systems are there as well (it IS a Dash after all):

#3 Hydraulic system exclusively powers the elevators (they are not connected to the yoke via cables and so require hydraulics to operate). It operates in standby mode, keeping a reservoir at 3000psi during normal operation. If either #1 or #2 hydraulics lose pressure in flight, either engine fails or the system is manually activated, the valve opens and pressure will be admitted to the #3 elevator actuators.

And the fourth hydraulic system uses good old muscle grease - a lever can be installed in a pump found below a hatch in the cockpit floor in order to manually pump down the landing gear in case of an abnormal extension. This levers plane of operation was selected such as to maximise discomfort in either pilot having to struggle with it all through the about 100 strokes it takes. But not all is lost: I had to run the alternate gear extension once and found that pumping was not needed - the gear fell down into its locks simply by gravity; in this case the checklist allows skipping the fitness training.

The -300 is similar with regards to #1 and #4 system, but as the elevator is not powered here, #3 system is not installed. There is a little feature on #2 (on aircraft that have received a certain mod whose number escapes me at the moment): the system has an electric driven pump in addition to the engine driven and the PTU to supply pressure. Most of the system is encapsuled in the tail to keep the pipes short. This is to keep on supplying power to the rudder in case of major hydraulic or power plant malfunctions - the rudder can run on #2 as long as there is electric power, the shutdown valve in the tail is closed and there is fluid left in that part of the system.

[spannersatcx]

You are quite right re 3000 psi being achieved prior to idle speed during the start sequence. However sub idle means any rpm below idle including in the area from 0 to 5 or 6 or 7%. I doubt that you would get 3000 psi at those low rpms.

hmmm, I'd have to check but you will get (on some a/c) 3000psi way below idle, I did a dry motor on a 744 CF6-80 today, just to check the start valve, got to about 3% N2 and the hyd fault or sys light went out before I switched the starter off, that light goes out around 1800psi, when I get a chance I will have another look and at a 330 as well.

[dhardesthard]

I believe that my statement is still accurate in that the hydraulic pressure will fall to below 3000 psi below normal idle speed. I did not say how far below but for argument sake 1/2 or 1% is below normal idle speed and you are certainly not going to get 3000 psi at 1%. Your hydraulic "light" that you refer to is a low pressure light and therefore will go out as the pressure increases to or reduces past a certain level. That light would be set to trigger at BELOW the NORMAL hydraulic pressure. Once again, if the hydraulic pressure(normal) is 3000 psi at idle rpm then it must at some time reduce to less than 3000 psi as the engine goes BELOW the normal idle speed, which is what I said.

[grounded27]

Next time I idle a motor I will pay more attention, I believe I was looking at a pw4000 on an MD-11 and it developed 3k psi by 10% N2.

[fizz57]

Aren't the EDP's positive displacement pumps? The question to ask is not what pressure it reaches when turning at low speed, but what will happen to that pressure if you put any demand on it.

[EW73]

Exactly, same with the airplanes I'm used to, at very low RPMs during starting, the hydraulic pressures are up fairly quickly, but it's pressure, not capacity until the pump RPM gets somewhere near normal.

Also, did I see someone earlier mention that he can run both aircon packs from one engine on a twin!
Not where I come from, a 737NG!

EW73

[FE Hoppy]

The E-jets idle the hydraulic pumps during engine starts to reduce starter loads so you don't see pressure until the start is well under way.( this is for in flight starts) Also for EW73, the E-jets can run 2 packs from one engine but the reduced flow restricts the aircraft to 31000ft. Above this it wouldn't meet the required lbs of air per passenger per minute. Some other aircraft are restricted to lower altitudes in the same condition.

[grounded27]

Aren't the EDP's positive displacement pumps? The question to ask is not what pressure it reaches when turning at low speed, but what will happen to that pressure if you put any demand on it.

You now have me recalling my DC-10 days, the electric pumps would often fault a full A/P systems RTS when used. 2 electric pumps feeding the two RMP's could not maintain the pressure upon demand. It was common practice to dry motor #2 engine, the output (volume) was much greater.