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

[Eddie]

A windmilling engine will produce some hydraulic pressure. As the engine decelerates to windmilling, for a short period of time (less than 60 seconds), this pressure may be enough to provide normal hydraulic operations

 

In more simple terms, as the engine spins down from the flight rpm range it MAY (assuming the EMAD, PTO shaft, AMAD, and Hyd Pump are all serviceable) continue to pump enough hyd oil to provide a usable pressure in the system for UP TO 60 seconds (depending on the rpm at engine shutdown and airflow etc.) assuming no physical damage to the core engine.

 

What that means in practice is that you have a few seconds to react to that failure. In the case of a single engine failure in the A-10 normal operation of the primary flight controls will remain unless it's a dual engine failure. A dual engine failure would require selection of MRFCS to retain aircraft control.

 

Yes a windmilling engine will motor the hyd pump (and electrical generator) provided the accessory drive is serviceable, however the speed that the high pressure compressor turns won't be sufficient to provide full system pressure (or even close to it). That amount of pressure supplied will be highly unlikely to be able to overcome the static friction of the actuators to move them at all, let alone provide normal function. For example I could hand you a control actuator from pretty much any aircraft and you would not be able to move extend or retract it yourself unless it's integrity was compromised (this is also why a/c flaps don't drop with no hyd pressure), a few hundred psi of pressure isn't going to be able to either.

 

The second you introduce battle damage and you can be pretty certain that any hyd integrity is gone. You can snap a hyd pipe easily with your hands, shrapnel etc has no problem doing it. And they run all throughout any aircraft. But that's perhaps another, more complex, discussion.

 

And to reiterate the point, these statement are not being made based on an untrained interpretation of a technical publication, but my experience with the systems in question (not the A-10C, however these things are not particularly type specific).

 

If as sobek suggests it's a case of not having the data to model the pump flow rates accurately then that is reasonable. However in such a case having the system produce zero pressure would be more accurate an estimation and result in a closer to reality aircraft behaviour.

[eaglecash867]

Would it help to have a -1 for the A-10C so everybody is playing from the same sheet of music when it comes to troubleshooting emergency procedures and how the A-10C in DCS responds?

[Eddie]

Why do the ailerons and elevators drop on an A320 without hydraulic pressure and the rudder moves with the wind?

 

Significantly larger control surfaces with more weight and of course more area for any airflow to act on and a different hyd system design (the actuators must have open return valves on shutdown). An installed control surface will happily act as a lever to move an unpowered actuator (assuming an open value for fluid to return through). It's just a matter of being able to exert enough force, which you can't do without a suitable lever. It's why doing it the other way around (actuator moving the control surface, especially under heavy air loads) requires ~3000 psi of system pressure. Low pressure isn't going to just move the control surfaces more slowly, it just won't move them at all (depending on air loads, and the actual pressure available of course).

[Sierra99]

They love all their modules equally.

 

Spoken like the true Father figure of the forums you are...

:thumbup:

[bkthunder]

 

If as sobek suggests it's a case of not having the data to model the pump flow rates accurately then that is reasonable. However in such a case having the system produce zero pressure would be more accurate an estimation and result in a closer to reality aircraft behaviour.

 

This.

[Scaley]

If as sobek suggests it's a case of not having the data to model the pump flow rates accurately then that is reasonable. However in such a case having the system produce zero pressure would be more accurate an estimation and result in a closer to reality aircraft behaviour.

 

This is what this boils down to in the finish really (and the same could be said about the repeated engine power debate). Accessing the technical specs of the engines in such a level of detail to actually know how the components are constructed is reasonably difficult. This means any system model designed component-up will contain some estimates. Mostly these produce reasonable behaviour.

 

Being as we do have (as a community) access to the aircraft flight manual we can see if the aircraft system behaviours match what the manual says they should be. In certain cases (like the hyd pressure on engine failure) they clearly don't. The model written may be largely sound, but for some reason it's producing behaviour divergent from how we know the real system behalves (assuming USAF documents are accurate). This divergent behaviour is probably due to missing data when the model was built being replaced by estimates.

 

In such cases even if we don't know exactly the components of the model that are inaccurate, parameters can be altered to produce a total system behaviour closer to the known behaviour.

[justinm11]

Wow! I didn't realise what I'd start haha I stepped away for a few days...I agree with Eddie and a few people above. In a game where there is serious chance of an engine failure and or damage I think that the systems should react realistically. I don't care what the pump can put out volume wise, where it's connected to the engine or any of that stuff, as stated above, I'm the pilot not an engineer. What matters to me is that in the event of a left engine failure at refusal speed, I have only a few seconds to get the gear up before pressure bleeds to zero and I can no longer retract the gear. Having pressure drop to zero in the event of an engine failure would require you to use airplanes emergency systems the way they were designed. Thats the way I read the manual, and I think thats all that needs to be done to make it react realistically. In the event of an engine failure on either the left or right side, you have only maybe 20 seconds before the pressure starts to bleed off. Any usage of that system causes the pressure to bleed off faster and once it's at zero, thats it, it's not coming back. I'm not programmer though, so maybe it's not that simple. Either way, it would be a better system then what is currently in place. Very happy to see that it's being looked at!

 

 

*Edit* Just did some further testing

 

In the mission as above I set another failure, this time to failure the left hydraulics 20 seconds after the left engine failed. It produced slightly better results. When the engine failed at about 20 feet in the air, I pulled the gear up and retraction was normal. 20 seconds after that the pressure dropped to around 500psi. I climbed to a safe altitude, lowered the gear and tried to raise them again. They would only come up about halfway and hang. They would extend normally, but would not fully retract. I expected no movement at all in the retraction sequence, but at least it's better than having the operate almost normally. Mind this only works in my very specific situation where I planned an engine failure at low speed, and low altitude in the takeoff configuration (One of the harder non-combat flying skills IMO). Without setting the hydraulic system to also fail, I could raise and lower the gear repeatedly without much issue.

Edited August 21, 2016 by justinm11

[NineLine]

 

*Edit* Just did some further testing

 

In the mission as above I set another failure, this time to failure the left hydraulics 20 seconds after the left engine failed. It produced slightly better results. When the engine failed at about 20 feet in the air, I pulled the gear up and retraction was normal. 20 seconds after that the pressure dropped to around 500psi. I climbed to a safe altitude, lowered the gear and tried to raise them again. They would only come up about halfway and hang. They would extend normally, but would not fully retract. I expected no movement at all in the retraction sequence, but at least it's better than having the operate almost normally. Mind this only works in my very specific situation where I planned an engine failure at low speed, and low altitude in the takeoff configuration (One of the harder non-combat flying skills IMO). Without setting the hydraulic system to also fail, I could raise and lower the gear repeatedly without much issue.

 

 

Interesting, thanks for taking the time to test it. Sounds more reasonable than what was originally thought.

[sobek]

Sounds more reasonable than what was originally thought.

 

That test had nothing to do with the originally lamented issue. He set the hydraulic system to fail, not just the engine. Nobody really questioned that the hydraulically operated systems won't work when there is no pressure. The issue is that there is pressure even when the engine is only windmilling.

[justinm11]

I set both the engine and the hydraulic system to fail in an effort to see that there was a realistic outcome from failing both. It still wasn't perfect, but it was a bit better. Even with a failure of the hydraulic system, pressure still shows in the system. My point was that maybe there could be a way that in the event of an engine failure, a quick work around would be to fail the hydraulic system a few seconds after. Either way, there's something a bit off here, but theres light at the end of the tunnel I think.

[Snoopy]

I don't know if this is enough information to fix the issue, but wanted to share what the TS (troubleshooting guide) for maintenance says concerning the A-10 hydraulic system.

 

It still doesn't say in "black and white" (except the statement "With the engine operating" below) anything about a windmilling engine shouldn't produce enough hydraulic power to work the system, although I know from real world knowledge that is the case.

 

Engine-Driven Hydraulic Pump

The major components of the engine-driven hydraulic pump are the geroter pump, the hanger, nine pistons, nine cylinder barrels, a compensator housing, an auxiliary pump (cooling) relief valve, and internal drive shafts. The engine-driven pump is mounted on the top right aft face of the accessory gear box of each engine.

 

The pump maintains a rated discharge pressure of 3100 psi (±75) (nominal pressure is 3000 psi).

 

Minimum full flow pressure is 2950 psi. The pump is capable of delivering hydraulic fluid at 43 (±0.2) gpm while operating at a speed of 5870 rpm.

 

The geroter pump provides the means for depressurizing the engine-driven hydraulic pump for reduced torque during engine startup. A check valve downstream of the engine-driven hydraulic pump prevents reversal of flow at the pump to prevent the engine from rotating while an external hydraulic power source (such as a test stand) is in use.

 

Fluid from the reservoir enters the inlet supply port in the engine-driven pump (EDP), where it is directed to the geroter (gear) pump (located in the EDP port cap), the pump rotating group, and the compensating valve. As the speed increases, the EDP discharge remains depressurized, until the pump speed reaches 2200 - 2800 rpm, at which time the outlet immediately changes to rated discharge pressure. Geroter pump discharge pressure is determined by its discharge flow rate through sensing orifices until the geroter relief valve setting is reached. The discharge pressure of the geroter pump pressurizes the compensator bias piston, varying its position, thus changing the pump pressure. When the bias piston is unloaded, the EDP is balanced and ported so that it generates only 725 psi maximum. At rest, the bias piston is spring-loaded against its adjustment stop. When the pump speed reaches the desired 2200 - 2800 rpm (37 to 47% engine core speed), the increased flow from the gerotor pump increases its discharge pressure across the speed-sensing orifice and the startup orifice, thus increasing the pressure differential across the bias piston, which causes it to move and cut off the startup orifice. The cutoff of the start-up orifice results in a rapid increase in pressure behind the bias piston, snapping it onto the normal run position and providing EDP discharge flow at rated pressure. Operation of the pump at speeds above 2200 - 2800 rpm is of the standard variable displacement EDP and compensation configuration.

 

In addition, the integral gerotor pump works together with the compensating valve-to serve as an unloading network to provide proportional depressurization of the EDP discharge as speed is reduced to between 2800 - 1600 rpm. When the EDP drops to the desired 2800 - 1600 rpm, the decreasing flow from the gerotor pump decreases its discharge pressure across the speed-sensing orifice. The lowering pressure permits bias piston movement in proportion to the gerotor discharge pressure. The speed-sensing orifice and the compensator spring rates are selected to shape the EDP discharge pressure to provide a smooth pressure transition as the speed reduces to the 1600 - 1200 rpm range. At this point, the bias piston backs off to the 725 psi maximum discharge control point and the startup orifice opens, thus unloading the gerotor pump and allowing the bias piston to bottom against the adjusting screw.

 

The EDP discharge pressure then drops below the 725 psi maximum dropout pressure and remains at the unpressurized discharge level until the pump stops rotating. Until the 725 psi maximum dropout pressure is reached, the EDP will remain on the system. If the EDP speed drops to the 1500 psi discharge point, for example, a speed increase would result in a proportional buildup to rated pressure at the speed level where the decay started, 1600 - 2800 rpm. A relief valve in the pump reduces the load on the gerotor pump as its output flow increases. Instead of directing all flow through the orifices (speed-sensing and startup), a portion is bypassed through the relief valve and reduces the discharge pressure of the gerotor pump. At rated speed, the combination of gerotor pump output and main pump internal leakage provides a flow of 4.1 gpm through the cooling loop of the gerotor pump and air/oil heat exchanger, and reduces heat rejection of the pump

 

General Hydraulic System Operation

Hydraulic power at approximately 3000 psi is supplied to operate the left and right hydraulic systems. With the engine operating, hydraulic fluid from the reservoir enters the engine-driven pump (EDP) through the pump inlet supply port.

 

Fluid from the case return port of the EDP flows through the hydraulic air/oil heat exchanger (cooler) to the R5 port of the supply module. The fluid then goes through the return filter back to the reservoir through the R4 reservoir return. If the return filter element becomes clogged, the return filter bypass valve opens, permitting return fluid to bypass the return filter and flow directly to the reservoir through the R4 reservoir return. Pressurized fluid flows from the EDP pressure out port through a check valve at the P1 pump pressure port of the module to the supply module. The pump output fluid is then filtered in the module by the pressure filter.

[Hansolo]

Thank you very much Snoopy for your valuable information. Good to have you back, Sir. A small questions if you do not mind.

 

1. Looking at the pictures in post #2 of this thread (also Figure FO-6 of T.O. 1A-10A-1) it seems like the APU is capable of supplying hydraulic power to right or left system via a a changeover switch/valve. Is this something which can be done from the cockpit or is it solely a mechanical one for maintennance?

 

2. Just to make heads and tails of it all the hydraulic reservoir's are the ones shown in Jake Melanpy 'The modern Hog guide' page 55 top and the accumulators are in same book page 43 bottom, right?

 

3. Last but not least. If I understand the above correct (and I may not) then there shouldn't be any pressure in the hydraulic system until EDP reaches 2200 - 2800 rpm (37 to 47% engine core speed).

 

Again good to have you back Sir.

 

All the best

Hans

Edited September 26, 2016 by Hansolo
Post no was wrong

[Yo-Yo]

I don't know if this is enough information to fix the issue, but wanted to share what the TS (troubleshooting guide) for maintenance says concerning the A-10 hydraulic system.

 

It still doesn't say in "black and white" (except the statement "With the engine operating" below) anything about a windmilling engine shouldn't produce enough hydraulic power to work the system, although I know from real world knowledge that is the case.

 

Engine-Driven Hydraulic Pump

The major components of the engine-driven hydraulic pump are the geroter pump, the hanger, nine pistons, nine cylinder barrels, a compensator housing, an auxiliary pump (cooling) relief valve, and internal drive shafts. The engine-driven pump is mounted on the top right aft face of the accessory gear box of each engine.

 

The pump maintains a rated discharge pressure of 3100 psi (±75) (nominal pressure is 3000 psi).

 

Minimum full flow pressure is 2950 psi. The pump is capable of delivering hydraulic fluid at 43 (±0.2) gpm while operating at a speed of 5870 rpm.

 

The geroter pump provides the means for depressurizing the engine-driven hydraulic pump for reduced torque during engine startup. A check valve downstream of the engine-driven hydraulic pump prevents reversal of flow at the pump to prevent the engine from rotating while an external hydraulic power source (such as a test stand) is in use.

 

Fluid from the reservoir enters the inlet supply port in the engine-driven pump (EDP), where it is directed to the geroter (gear) pump (located in the EDP port cap), the pump rotating group, and the compensating valve. As the speed increases, the EDP discharge remains depressurized, until the pump speed reaches 2200 - 2800 rpm, at which time the outlet immediately changes to rated discharge pressure. Geroter pump discharge pressure is determined by its discharge flow rate through sensing orifices until the geroter relief valve setting is reached. The discharge pressure of the geroter pump pressurizes the compensator bias piston, varying its position, thus changing the pump pressure. When the bias piston is unloaded, the EDP is balanced and ported so that it generates only 725 psi maximum. At rest, the bias piston is spring-loaded against its adjustment stop. When the pump speed reaches the desired 2200 - 2800 rpm (37 to 47% engine core speed), the increased flow from the gerotor pump increases its discharge pressure across the speed-sensing orifice and the startup orifice, thus increasing the pressure differential across the bias piston, which causes it to move and cut off the startup orifice. The cutoff of the start-up orifice results in a rapid increase in pressure behind the bias piston, snapping it onto the normal run position and providing EDP discharge flow at rated pressure. Operation of the pump at speeds above 2200 - 2800 rpm is of the standard variable displacement EDP and compensation configuration.

 

In addition, the integral gerotor pump works together with the compensating valve-to serve as an unloading network to provide proportional depressurization of the EDP discharge as speed is reduced to between 2800 - 1600 rpm. When the EDP drops to the desired 2800 - 1600 rpm, the decreasing flow from the gerotor pump decreases its discharge pressure across the speed-sensing orifice. The lowering pressure permits bias piston movement in proportion to the gerotor discharge pressure. The speed-sensing orifice and the compensator spring rates are selected to shape the EDP discharge pressure to provide a smooth pressure transition as the speed reduces to the 1600 - 1200 rpm range. At this point, the bias piston backs off to the 725 psi maximum discharge control point and the startup orifice opens, thus unloading the gerotor pump and allowing the bias piston to bottom against the adjusting screw.

 

The EDP discharge pressure then drops below the 725 psi maximum dropout pressure and remains at the unpressurized discharge level until the pump stops rotating. Until the 725 psi maximum dropout pressure is reached, the EDP will remain on the system. If the EDP speed drops to the 1500 psi discharge point, for example, a speed increase would result in a proportional buildup to rated pressure at the speed level where the decay started, 1600 - 2800 rpm. A relief valve in the pump reduces the load on the gerotor pump as its output flow increases. Instead of directing all flow through the orifices (speed-sensing and startup), a portion is bypassed through the relief valve and reduces the discharge pressure of the gerotor pump. At rated speed, the combination of gerotor pump output and main pump internal leakage provides a flow of 4.1 gpm through the cooling loop of the gerotor pump and air/oil heat exchanger, and reduces heat rejection of the pump

 

General Hydraulic System Operation

Hydraulic power at approximately 3000 psi is supplied to operate the left and right hydraulic systems. With the engine operating, hydraulic fluid from the reservoir enters the engine-driven pump (EDP) through the pump inlet supply port.

 

Fluid from the case return port of the EDP flows through the hydraulic air/oil heat exchanger (cooler) to the R5 port of the supply module. The fluid then goes through the return filter back to the reservoir through the R4 reservoir return. If the return filter element becomes clogged, the return filter bypass valve opens, permitting return fluid to bypass the return filter and flow directly to the reservoir through the R4 reservoir return. Pressurized fluid flows from the EDP pressure out port through a check valve at the P1 pump pressure port of the module to the supply module. The pump output fluid is then filtered in the module by the pressure filter.

 

THank you very much! This is the starting point engineers have to start communication with. :)

Unfortunately, we did not have this detailed description as we were working on the systems, so we used the info of the available pumps from the different planes.

 

Is it possible to take a look at the schematics to be sure as we are starting to model it?

Edited September 26, 2016 by Yo-Yo

[Snoopy]

1. Looking at the pictures in post #2 of this thread (also Figure FO-6 of T.O. 1A-10A-1) it seems like the APU is capable of supplying hydraulic power to right or left system via a a changeover switch/valve. Is this something which can be done from the cockpit or is it solely a mechanical one for maintenance?

 

It is not available from the cockpit. The handle is located just forward of the APU. It is accessed through a small panel that has been modified to not allow the panel to close with the hydro handle in the up (right system) or down (left system) position and is strictly for maintenance purposes.

 

2. Just to make heads and tails of it all the hydraulic reservoir's are the ones shown in Jake Melanpy 'The modern Hog guide' page 55 top and the accumulators are in same book page 43 bottom, right?

 

I'll make a note to check the book when I get home from work today.

 

3. Last but not least. If I understand the above correct (and I may not) then there shouldn't be any pressure in the hydraulic system until EDP reaches 2200 - 2800 rpm (37 to 47% engine core speed).

 

That is correct.

[Hansolo]

Many thanks for the answer and for looking into the subject.

 

Cheers

Hans

[Snoopy]

 

Is it possible to take a look at the schematics to be sure as we are starting to model it?

 

I don't have a copy of the schematics but I'll see what I can dig up.

 

2. Just to make heads and tails of it all the hydraulic reservoir's are the ones shown in Jake Melanpy 'The modern Hog guide' page 55 top and the accumulators are in same book page 43 bottom, right?

 

Page 43, lower left is the emergency accumulator bottles. Page 54, two middle pictures are of the left reservoir and accumulators, page 55, top left picture is the right reservoir and accumulators.

Edited September 27, 2016 by Snoopy

[SCU]

as we are starting to model it

 

Does this mean the proposed information will actually be implemented in the DCS A-10C?

[NineLine]

Does this mean the proposed information will actually be implemented in the DCS A-10C?

 

Means he is taking a look at what Paul has to offer up.

[SCU]

Means he is taking a look at what Paul has to offer up.

Either way I'm happy that new info or incorrectness are getting looked at for this oldish module :).

[bkthunder]

Glad to see this being looked at and hopefully made close to RL behavior

[Hansolo]

Thanks a lot Snoopy for the assistance :thumbup:

 

Cheers

Hans

[NineLine]

This is a bug thread if you dont have anything meaningful to bring to this thread please dont muddy the waters so that good information gets lost among it. If you want to have long meaningless arguments and quote-fests, you know the forum that enjoys that.

[Snoopy]

 

Is it possible to take a look at the schematics to be sure as we are starting to model it?

 

Schematics sent to Sith.

[Snoopy]

Curious of the information I provided was enough for Yo-Yo to understand the issue or not?

[NineLine]

I think they may all be on vacation now, but I sent him a link to this on Skype, so will find out one way or the other.