Su-27 hydraulic systems

[Fouga]

It seems that with the new PFM Su-27, there was also some modifications on the hydraulic systems logic :

 

In case of Hydraulic failure (as defined in the ME), you rapidly loose any hydraulic pressure and can't move airbrake, flaps and any other control surfaces (on wings and stabilisers) which rapidly leads you to a catastrophic loss of control of the plane. That corresponds to a failure of both hydraulic systems.

 

In the past, In case of Hydraulic failure, you were not able to move the airbrake and flaps but could always move the different control surfaces and get back the plane to an airfield.

That was corresponding to a failure of one of the two hydraulic systems (assuming the flaps were controlled with the same hydraulic system as the airbrake).

 

If you switch off or loose one (or two) engine(s), you will keep every system functional as long as it remains some RPM – which is the case while you are flying.

 

After some tests on the ground, I concluded that :

- the Hydraulic system #1 is related to the left engine and controls the nose wheel steering

- the Hydraulic system #2 is related to the right engine and controls the airbrake

- Both Hydraulic systems are controlling the different control surfaces including flaps

 

To visualise the drop of pressure in those hydraulic systems, we are missing animated pressure gauges (they are always showing full pressure), I hope this will be added in a further update of the flanker.

 

 

I also tested Hydraulic systems of the other DCS-like planes of FC3 :

Su-25 & Su-25T loose their airbrake, flaps and nose wheel steering in case of drop of the hydraulic system #1 pressure. They will also loose the ability to release / retract landing gear in case of drop of the hydraulic system #2 pressure but they will keep their manoeuvrability in case of failure of both hydraulic systems – this might be because they are not using fly-by-wire.

In case of failure, you can monitor the remaining hydraulic pressure thanks to the accurate gauges.

 

F-15C only looses its airbrake and nose wheel steering in case of failure of both hydraulic systems, it cannot also retract the landing gear. But it will remain controlable as every control surfaces keep on working fine. Is this the case IRL ?

 

A-10A doesn't loose any system in case of failure of both hydraulic systems.

Edited December 30, 2014 by Fouga

[RvETito]

I notice another interesting fact. Pulling G's right after take-off is dramatically increasing the time for landing gear retraction. I think this is a bit of an overkill. True, the hydraulic pressure should overcome few times bigger weight but 210 bars at a good flow rate what a variable displacement pump is able to provide is a pretty solid power source. It feels like the flow supplied by the pump(s) is decreasing which is not right. There is plenty of footage of various modern fighters retracting their gears while maneuvering and can't notice a difference while the Su-27 in DCS takes ages to retract the gear if you're pulling 3-4 G's.

[Shadow KT]

For the A-10 might as well use the C model manual as the hydro systems are very detailed there as far I remember and as it is almost the same plane I'd believe that the hydro systems are pretty much the same

 

P.S. btw nicely constructed thread and finds

[aap_flanker]

I notice another interesting fact. Pulling G's right after take-off is dramatically increasing the time for landing gear retraction. I think this is a bit of an overkill. True, the hydraulic pressure should overcome few times bigger weight but 210 bars at a good flow rate what a variable displacement pump is able to provide is a pretty solid power source. It feels like the flow supplied by the pump(s) is decreasing which is not right. There is plenty of footage of various modern fighters retracting their gears while maneuvering and can't notice a difference while the Su-27 in DCS takes ages to retract the gear if you're pulling 3-4 G's.

That's so true...

And at take off the engines are at maximum rpm, so the same for all of the accesories attached to it (in this case the hydraulic pump), also any hydraulic system has an accumulator that provides some "help" in case the pump its not supplying enough flow.