Left Engine = Left Hydraulics?

[roadrabbit]

Exploring the hydraulics systems on the DCS A-10C I shut down the left engine. I expected to lose the use of the flaps, nosewheel steering, wheel brakes, anti-skid and the hydraulic control of the left elevator and rudder actuators (along with loss of dual channel pitch and yaw SAS).

 

But no - I still had nosewheel steering and wheel brakes.The SAS warnings DID come up on the warning panel. So what is going on?

 

This all came about because I wanted to assign a "usable" keyboard stroke to activate the Emergency Brake - using HOTAS have you tried to operate the combination of 'W RWin'? Or maybe you have no trouble with mouse operation of the Emergency Brakes lever in the virtual cockpit :lol:

Look out grass - here we come!

[Robin_Hood]

Have you used the systems enough after losing the engine ? Some hydraulic pressure is left (but does not replenish anymore) when the engine is shut down and decreases as the system is being used - you should see the hydro indicator going down the more you use thoses relevant controls you mentionned. When it falls too low, systems stop responding.

 

I remember this used to work, but I'm not sure I tested thoroughly differentiating between left and right hydraulics.

[MTFDarkEagle]

The pressure will (if you don't do anything) bleed off slowly (talking minutes). If you use systems which use the L-HYD system (as you rightly pointed out) the pressure will bleed off quickly.

[Snoopy]

Some hydraulic pressure is left.....

 

That's actually a bug but for some reason ED doesn't believe me.

[MTFDarkEagle]

That's actually a bug but for some reason ED doesn't believe me.

 

So the pressure bleeds off completely when the engine is shut down?

[Snoopy]

Yes. All your left with is the left or right accumulator precharges which isn't enough to do anything. If we had as much pressure left real world as DCS has most of the hydraulic EPs (Emergency Procedures) wouldn't be needed.

 

When running engines on the ground the drop in pressure is immediate. In the air a small amount is generated by the fans spinning but again not enough to be meaningful. The psi varies by engine & aircraft.

[MTFDarkEagle]

Yes. All your left with is the left or right accumulator precharges which isn't enough to do anything. If we had as much pressure left real world as DCS has most of the hydraulic EPs (Emergency Procedures) wouldn't be needed.

 

When running engines on the ground the drop in pressure is immediate. In the air a small amount is generated by the fans spinning but again not enough to be meaningful. The psi varies by engine & aircraft.

 

Aha! Very interesting!

So no intention from ED to fix this? :(

[Robin_Hood]

Indeed, good to know! Thank you, paulrkiii :smartass:

[Eddie]

Yep, one of several long running bugs/inaccuracies with the A-10C that have long been reported.

[Sheepherder]

The actual reasoning behind it is pretty mundane: hydraulic fluid is largely incompressible, so for all intents and purposes they don't store energy. You can have a powered off hydraulic system reading 5k, but crack a valve a hair and the gauge will immediately go from 5k to 0.

Edited October 2, 2013 by Sheepherder

[MTFDarkEagle]

The actual reasoning behind it is pretty mundane: hydraulic fluid is largely incompressible, so for all intents and purposes they don't store energy. You can have a powered off hydraulic system reading 5k, but crack a valve a hair and the gauge will immediately go from 5k to 0.

 

True but one could also assume there would be some kind of accumulator.

[howie87]

Yeah, there is an accumulator but as snoopy said...

 

Yes. All your left with is the left or right accumulator precharges which isn't enough to do anything. If we had as much pressure left real world as DCS has most of the hydraulic EPs (Emergency Procedures) wouldn't be needed.

 

When running engines on the ground the drop in pressure is immediate. In the air a small amount is generated by the fans spinning but again not enough to be meaningful. The psi varies by engine & aircraft.

[roadrabbit]

The actual reasoning behind it is pretty mundane: hydraulic fluid is largely incompressible, so for all intents and purposes they don't store energy. You can have a powered off hydraulic system reading 5k, but crack a valve a hair and the gauge will immediately go from 5k to 0.

 

Very useful and informative thread.

 

Re the above: actually a hydaulic reservoir doesn't just contain hydraulic fluid - it also contains gas (air?) which is compressible. Other aircraft have reservoirs at e.g. 3,000 psi, which is often enough stored pressure to operate emergency brakes following an RTO. The trick is NOT to pump the brakes as you will, as described previously, use up all the stored pressure. :smartass:

Edited October 2, 2013 by roadrabbit
emphasis

[Eddie]

Very useful and informative thread.

 

Re the above: actually a hydaulic reservoir doesn't just contain hydraulic fluid - it also contains gas (air?) which is compressible. Other aircraft have reservoirs at e.g. 3,000 psi, which is often enough stored pressure to operate emergency brakes following an RTO. The trick is NOT to pump the brakes as you will, as described previously, use up all the stored pressure. :smartass:

 

Well, to be pedantic, a hyd reservoir won't typically store pressure only increase the systems fluid capacity. The accumulators however do store pressure, using nitrogen bladders which are compressed as fluid is pumped into the system.

[Snoopy]

it also contains gas (air?)

 

Negative, if there is air in an A-10 reservoir that means there is air in the hydraulic system which is a bad thing.

 

The only air (nitrogen), as Eddie pointed out is in the accumulators.

[Hansolo]

Good informative thread thanks :thumbup:

 

A small picture for reference which shows a accumulator with bladder which contains nitrogen, and how it works.

 

Cheers

Hans

[roadrabbit]

Good informative thread thanks :thumbup:

 

A small picture for reference which shows a accumulator with bladder which contains nitrogen, and how it works.

 

Cheers

Hans

 

:music_whistling: Fancy me forgetting that the gas is in a bladder!

[Comrade Vodka]

Yes. All your left with is the left or right accumulator precharges which isn't enough to do anything. If we had as much pressure left real world as DCS has most of the hydraulic EPs (Emergency Procedures) wouldn't be needed.

 

When running engines on the ground the drop in pressure is immediate. In the air a small amount is generated by the fans spinning but again not enough to be meaningful. The psi varies by engine & aircraft.

 

That is interesting.....because as much as I can recall, all the military aircraft I've worked on store the pressure after shutdown until it's bled off via moving flight controls. Pity ED are not taking your advice though Paul, as if anyone should know, it would be you.

 

It does make me wonder where it goes though.....maybe a valve opens when it detects a drop in pressure as the EDP (hyd pump) starts to slow up :dontgetit:

[tomcatter]

Yep, one of several long running bugs/inaccuracies with the A-10C that have long been reported.

 

I´m reading with much interest all the info here, amazing what you guys make me learn.

 

That´s why I love aircraft, all the brain power needed behind the engineering needed to make a man fly..¡¡¡¡

 

o Hell my english is horrible...

 

By the way Eddie, which more bugs/inaccuracies can we find in the Hog as is today....?

 

Don´t want to complain on anythig, just looking for the info to know where our Hog differs frol RL one..

Edited October 2, 2013 by tomcatter
re-thinking of the question

[PondLife]

Accumulators usually only store enough pressure to work the brakes for a short time. On some aircraft there is an EHP or electro hydronic pump (not an A10) otherwise there's usually a manual way of pumping up the accumilatir for breaks on towing and for hydraulically operated canopies.

[Snoopy]

Per the -1

 

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.

 

Notice is say's short period, less than 60 seconds!

 

That is interesting.....because as much as I can recall, all the military aircraft I've worked on store the pressure after shutdown until it's bled off via moving flight controls.

 

Without the hydro pumps running the only pressure available is the accumulators and those are only to "stabilize" hydraulic pressure.

 

It doesn't matter if you are running engines, using APU for hydraulic power, or using a hydraulic test stand, as soon as they are shut down hydraulic power goes to zero.

 

Just an example of how quickly pressure bleeds off when shutting down an engine, one of our checks when we recover a jet is as soon as the #1 engine is shutdown and hydraulic pressure bleeds off (less than 60 seconds) the pilot cycles flight controls to make sure they all operate off the right system only. We do the same check when starting #1, as soon as 1 is up and stable they cycle the controls to make sure all primary work off of only the left system.

[roadrabbit]

Per the -1

 

 

 

Notice is say's short period, less than 60 seconds!

 

 

 

Without the hydro pumps running the only pressure available is the accumulators and those are only to "stabilize" hydraulic pressure.

 

It doesn't matter if you are running engines, using APU for hydraulic power, or using a hydraulic test stand, as soon as they are shut down hydraulic power goes to zero.

 

Just an example of how quickly pressure bleeds off when shutting down an engine, one of our checks when we recover a jet is as soon as the #1 engine is shutdown and hydraulic pressure bleeds off (less than 60 seconds) the pilot cycles flight controls to make sure they all operate off the right system only. We do the same check when starting #1, as soon as 1 is up and stable they cycle the controls to make sure all primary work off of only the left system.

 

I have just done some more checks of hydraulic action after shutting down the left engine. On the DCS A-10C the pressure remains at 3,400 psi provided you don't touch anything (I was stationary on a runway!). Exercising the flight controls didn't have any effect on hyd pressure and nor did moving the nosewheel. After more than 60 secs after shutdown (no hyd pressure reduction), cycling the wheelbrakes did have an effect and I was able to reduce the hyd pressure to an effective zero with about 10 cycles. Prior to this I did have effective nosewheel steering. Afterwards I had lost both wheelbrakes and nosewheel steering. I had probably lost hyd flap operation as well but the 'other' pilot :huh: forgot to check!

 

It may all seem a bit pedantic, but I feel I am really getting to know how this DCS ship operates.

 

One thing occurs to me: if you lost the left engine and rejected the take-off, it would be nice to know that a little (accumulator) hyd pressure was left to steer and brake the aircraft. Dealing with the primary effects of engine loss wouldn't leave much headspace to deal with alternate brakes and reduced steering capability. Just a thought :D

Edited October 2, 2013 by roadrabbit
spelling

[Snoopy]

One thing occurs to me: if you lost the left engine and rejected the take-off, it would be nice to know that a little (accumulator) hyd pressure was left to steer and brake the aircraft. Dealing with the primary effects of engine loss wouldn't leave much headspace to deal with alternate brakes and reduced steering capability. Just a thought :D

 

That's not what the accumulators are for. if you lost the left engine on takeoff you would still have all primary flight controls.

 

Here is a breakdown of what the left and right systems power respectively.

 

Left Hydraulic system:

• Flight control - Left rudder, left elevator, left and right aileron, flaps
  
• Landing gear - Landing gear extend and retract, wheel brakes, anti-skid, and NWS
  
• Armament - One half of gun drive

 

Right Hydraulic system:

• Flight control - Right rudder, right elevator, left and right aileron, speed brakes, slats
  
• Emergency Auxiliary landing gear systems extend, emergency wheel braking and associated accumulators
  
• Armament - One half of gun drive
  
• Air refueling - Slipway door and receptacle lock

 

Accumulators usually only store enough pressure to work the brakes for a short time. On some aircraft there is an EHP or electro hydronic pump (not an A10) otherwise there's usually a manual way of pumping up the accumilatir for breaks on towing and for hydraulically operated canopies.

 

Not on the A-10. We have 4 accumulators, one each on the RT and LT systems. Their only function is to regulate hydraulic pressure. Two more are located in the nose, one for emergency brake pressure and the other for auxiliary extension of the landing gear. Both emergency accumulators are powered by the right hydraulic system.

[howie87]

Awesome info paulrkiii. Wish ED would realise you know what you're talking about and fix it in DCS!

[roadrabbit]

That's not what the accumulators are for. if you lost the left engine on takeoff you would still have all primary flight controls.

 

 

:thumbup: Yes, I am agreeing with you - what I meant by primary effects was the assymetric power causing a swing, and the need to brake during an RTO, i.e. before take-off.

 

The primary controls are there to be used to counter the swing, but with a left engine failure you would have only right rudder powered (are they connected - both work in ED with zero left hyd pressure?) and no nosewheel steering. Avoiding going off the side of the runway would be your primary object, with going off the end of the runway being secondary (at first!). I now think that setting the lever switch on the control stick to Emergency Brakes (on the Thrustmaster HOTAS control stick) will be a good idea - as I've said elsewhere, using the keyboard as set requires two hands and 'looking in'!

 

Question: with a left engine failure will speedbrakes still be available? The manual suggests not, which seems at odds with how the systems are set.

Secondary question: If they do work with a left engine fail, is the RW RTO drill to try and extend them anyway?

Edited October 3, 2013 by roadrabbit
New information