A-10C Hydraulic System in event of left engine failure

Hello!

I was wondering if anybody had a diagram of how the hydraulic system in this aircraft is setup. I've been using the real A-10A manual to practice various types of emergencies (Engine failure at refusal speed) etc. I'm a little bit confused by how the hydraulic system works in the event of a failure.

I failed the left engine a few knots above refusal speed, continued the takeoff and everything seemed to react as normal. Gear took a while to fully retract (due to using residual pressure, and I got the airplane cleaned up. Ran through the checklist in the A-10A manual, which led me to turn off SAS switches, turn on the APU and turn on the APU generator. I used the fuel crossfeed switch to maintain fuel balance.

This is where the procedure gets murky for me. The left hydraulic system was showing good pressure. I did an emergency gear extension as per the checklist, and noted that "Normal brakes, flaps, nose wheel steering and antiskid would be unavailable. The left hydraulic system pressure had dropped to nearly zero by this point. Just as a test (It's training after all) I put the flaps down to see what kind of warning I would get. The flaps came down seemingly without issue and at normal speed, which I thought was odd. On landing, sure enough I had to use the emergency brake to slow down, and the nosewheel steering didn't work.

Did the flaps come down just because there was a bit of pressure remaining in the system? Or has there been a change in the A-10C that allows the flaps to be powered now by the right hand system? That's why I'd like to see a diagram. I noticed that in the A-10C manual provided by DCS that it says to just put flaps down like normal. Total flight time was about 15 minutes, from rotation to touchdown, if that matters.

*edit* I now see that a flap 0 approach should be flown to ensure adequate performance in the event of a missed approach, but my question still remains.

Thank you for the above pictures. The only thing I see connecting the two sides is the APU driven pump which after reading I think is a ground maintenance function. This led me into the right spot in the manual though. For anybody wondering (I will confirm this through tests) I continue to see reference to a seized engine causing an immediate loss of pressure to its associated hydraulic system. The engine in my scenario was windmilling during the approach which is probably why I still had a bit of pressure to lower the flaps. Once my speed reduced on the ground I lost the power to the system fully since the engine wasn't windmilling any more. This might explain my nearly full system pressure when I was flying higher at 200kts but why it bled off on approach. I suspect that I would not have been able to retract the flaps again on the ground though I didn't try it. I will post back with my findings for anybody who is interested.

This does seem to be the case in what I stated above. With the engine windmilling there will be enough pressure in the system to operate the gear, and flaps, albeit slowly. Pressure seems to stabilize around 1000psi and will drop off when operating any hydraulic equipment associated with that system. Pressure will slowly rebuild to around 1000psi at any time that the engine is still windmilling. Using the alternate gear extension will allow faster lowering of the gear. As soon as the engine stops windmilling say during the final stages of the landing rollout the pressure will drop to zero and the system will be inoperative. If anybody knows how to simulate a seized engine in flight please let me know. I'd like to try this in flight, but I couldn't get the engine to stop windmilling while flying.

This does seem to be the case in what I stated above. With the engine windmilling there will be enough pressure in the system to operate the gear, and flaps, albeit slowly. Pressure seems to stabilize around 1000psi and will drop off when operating any hydraulic equipment associated with that system. Pressure will slowly rebuild to around 1000psi at any time that the engine is still windmilling. Using the alternate gear extension will allow faster lowering of the gear. As soon as the engine stops windmilling say during the final stages of the landing rollout the pressure will drop to zero and the system will be inoperative. If anybody knows how to simulate a seized engine in flight please let me know. I'd like to try this in flight, but I couldn't get the engine to stop windmilling while flying.

This is a bug. In the real A-10 the windmilling doesn't produce enough pressure to operate the systems as it it possible in DCS. AFAIK this has been reported by people in the know, but never been acknowledged/fixed.

You won't be able to simulate the proper hydraulic consequences of an engine failure in Dcs :cry:

Dont believe everything you hear, this has been assigned to a dev responsible for these types of fixes, but would most likely be fairly low priority at this point because...

 

 

 

Isn't an exciting point for most people when they jump in and want to experience the A-10C... its not a blocking issue, therefore I cant see it being high priority right now.

Good to know it's noted by ED. IMO getting shot at and handling emergencies is a big part of the A10 flying experience. Of course if this was Fsx I'd say that would be a good extra, but in Dcs you're likely to have emergencies happen, so it's quite central.. The correct implementation of the consequences of these emergencies is something that a faithful sim should recreate.

Is it true that ED will give some love for the A-10 with 2.5 release?

Do you know exactly what is the pump delivery vs rpm? Do you know exactly the hydro-acc volume? Do you know exactly the dimensions and piston travel of the hydro-actuators?

 

What's the base for your conclusion?

 

 

 

And finally - how must the pressure of the pump be dependant on the rpm, for your mind?

I don't know, but then, why should I?

I'm using DCS A-10C to simulate how the plane is flown and operated, and challenge my piloting skills, not my engineering knowledge...

Sith already said the bug was acknowledged and assigned to an ED programmer to be fixed, so it seems the bug is confirmed. You obviously know the numbers, so why don't you share them with us? I for one would love to know such details :smilewink:

Maybe I can ask you a question: why can't we follow the procedures outlined in the a-10 manual, in case of engine failure? What happens in the sim differs from what is described in the RL manual, I'm not aware if any changes to the hydraulic systems between the A and C versions.

People that do have access to info like that, stated above, are banned.

Do you know exactly what is the pump delivery vs rpm? Do you know exactly the hydro-acc volume? Do you know exactly the dimensions and piston travel of the hydro-actuators?

 

What's the base for your conclusion?

 

 

 

And finally - how must the pressure of the pump be dependant on the rpm, for your mind?

It's not really anything to do with the pump. If the TF34 is anything like it's CF34 counterparts, or any free turbine, the accessories are not driven off the fan stage (N1), but through the gas generator (N2). The large RPM variances of N1 make it extremely difficult to make efficient accessory gearboxes driven off it.

N2 of a windmilling engine is negligible, as it's usually only in the range of 5-20% - not enough to provide any useful RPM at the accessory gearbox.

I've never seen an application where any accessories are driven off a fan stage. You want as much power to the fan as possible.

In addition, by combining the starter (in this care - an air turbine starter) and accessories in a single accessory gearbox, you save weight. You don't need a seperate gearbox to drive the N2 stage off the starter, and another to drive accessories. Ya get to combine both.

So in our case with the A-10 - the hydraulic engine-driven-pumps (EDP - Variable displacement constant pressure type) are driven off N2, not N1. If the engine is windmilling in flight, insufficient N2 RPM doesn't allow sufficient hydraulic pressure nor volume to be attained.

I mean, that the dispalcement of this pump is definitely low at low rpm, but the pressure remains almost the same because of basic principles of this pump.

But If the displacement of the pump is to low it will not reach the system working pressure (apr. 3000 PSI Mostely).

A variable displacement pump will be delivering its max volume per cycle if 3000 psi is not reached yet (bij angeling the wobbleplate to the max).

But if the RPM is to low, this volume/min is not enough to reach the 3000 PSI.

Simply because the oil is seeping away through the system components, to the return in the reservoir, to fast for the pump to compensate.

The pump can only reach the 3000 PSI if it is delivering enough volume/min of oil, so that there is a backpressure build up in the system of 3000 PSI.

If the system pressure is reached the pump will adjust to get a reduced volume/min.

Just to see if whe think alike...on this.

Greetings

Thanks,

I understand the reasoning behind it now and it sounds practical.

Yep..i think it is not easy to find out at what RPM the Pump is with a certain Fan and Core rpm.

And it seems to me that it is even harder to find out what the capacity of the pump is at a lower than normal RPM !!

Well ehhh...Good Luck with That :)

Thanks again.

I think it's a matter of the time to fill the accumulator volume. Now, it's about 30 seconds to reach 3000 psi IF NO MOVMEENT IS PERFORMED with the stick and rudder.

 

The main question is the maximal delivery of the pump at the certain rpm. As we had no exact pump specification (I think) we use pressure drop at the certain operation (like gear up, for example) and how fast it is built again.

I works fine if you know hydro-acc working volume and actuator dispalcement.

Yo-Yo, in an effort to further this without directly referencing material the I can't give you. Are you suggesting that all the aircrew flight manuals and emergency checklists are wrong and that there is no need for aircrew to worry about loss of hyd pressure with a windmilling engine?

If that is your intent, which is what comes across, then how can you possibly make this claim? What source are you basing this on?

And to raise another point, under what scenario do you believe MRFCS and other emergency systems in the A-10 are used for?

At present, in DCS there is no occasions where MRFCS is required, nor is there an occasion where control surface emergency disconnects are required.

It is also not necessary, at any time, to follow the A-10 emergency procedures with reference to engine/hydraulic system faults/failures as the failure modes of the real aircraft do no occur in DCS. Do you consider this to be correct?

If that is your intent, which is what comes across, then how can you possibly make this claim? What source are you basing this on?

What his post boils down to for me is that in the absence of correct information about the pump output at anything other than nominal RPM, they had to estimate the behaviour. Estimates are by their nature faulty. What you are seeing is the error stemming from having to estimate the behaviour. Yo-Yo isn't saying that the manual is wrong, he's saying that with the data he has available to him, it is not possible to model it better.

Knowing that the model is wrong is not enough to make a better model. It is only the first step.