Loss of hydraulics wasn't that bad

[Rongor]

Hey guys,

yesterday I lost hydraulics. After the Ekran told me there was a problem, I noticed both the main and the common hydraulics circuits showed zero indication. Yet besides losing the AP augmentation channels, I could continue my RTB just fine. I had to yank and keep the cyclic stick in weird positions at time, but as I was unable to trim, this was to be expected.

 

Now I wondering how I was able to maintain control at all after the hydraulics loss. As far as I'd expect from own RL experience, there is no way to apply reasonable steering forces with the controls without the amplifying hydraulic force. I mean, that's what it's job after all.

There is this hydraulics accumulator and of course we could assume, that my maintaining of control was supported by the remaining hydraulics pressure in the accumulators. The gauge showed the accumulator at around 80 %. Yet this indication never changed. However hard I did steering inputs, the indication didn't change at all.

 

So I am still clueless what happened exactly, how I could maintain control without any hydraulics and why the accumulators didn't show any pressure change. Sadly, hydraulics aren't among the well explained features in the flight manual.

 

Any ideas?

[AlphaOneSix]

It looks like you've simply run into something that isn't simulated very well.

[26-J39]

Hopefully BS3 will include "system refinement" as OP has mentioned.   As well as others i won't mention in this thread.

[Volk.]

I can confirm this - accumulator stays at about 80%.

The only thing that appears to drain it is each press of the wheelbrake drains it maybe 20-25%. Holding wheelbrake in doesn't appear to drain it (at least not very quickly) and control inputs from cyclic/collective appear to have zero effect on it. So some of the hydraulics loss and accumulator depletion is simulated.

Admittedly I popped gear before losing all hydro, though given some people often find they can't get the gear down after both hydraulics are lost I'd assume maybe that does bottom out the accumulator but doesn't quite get the job done, or alternately the gear even on emergency isn't fed from the accumulator.

 

This is with both hydraulic systems dead from damage (not simulated) and all the normal auto-switching from normal startup on to let the flight hydraulics get covered by common if main fails.

[Rongor]

Ok, so the bottom line appears to be:

- hydraulics system failures have some dubious effects but aren't really simulated deeply at the moment

- in critical hydraulic states, accumulators currently only get depleted by wheel braking

 

Btw Volk, I really like your youtube Ka-50 videos...

[Rogue Trooper]

It is very hard to replicate Hydraulic failure in a sim.

For sure you would need to pull your joystick around with some incredible force to manhandle that 9,000 Kg chopper.

That would be some serious FFB joystick.... I would love it if it was available and if I could afford it!

Edited June 14, 2021 by Rogue Trooper

[AlphaOneSix]

39 minutes ago, Rogue Trooper said:

It is very hard to replicate Hydraulic failure in a sim.

It's easy for the Ka-50. The controls just don't move. As far as buying a joystick to replicate it, I suppose you could just put a steel pipe into some concrete. 

[Quadg]

I like the way is simulated in the Huey.

even though its not realistic.

you start getting random stick inputs.

which are easy to deal with. At first.

so I carried on flying.

10 minutes later I'm flying a bucking bronco wishing I had landed straight away, while I still could, instead of trying to RTB.

 

so if you fly the huey and have a hydraulics problem, land straight away, like it says in the manual.

the simulation may not be accurate to real life, but it sure gets the point across.

 

[Reticuli]

1 hour ago, Rogue Trooper said:

It is very hard to replicate Hydraulic failure in a sim.

For sure you would need to pull your joystick around with some incredible force to manhandle that 9,000 Kg chopper.

That would be some serious FFB joystick.... I would love it if it was available and if I could afford it!

 

How hard is it to reduce control authority based on hydraulic pressure and have pressure fall faster when hydraulics are damaged based on how hard and frequently you move the controls?  Obviously at a certain point it's going to feed back and go to zero pretty fast, and certainly helos and unstable digital FBW fix-wing planes are going to use it up faster than a stable fixed-wing aircraft, but seems pretty easy to do beyond just having the wheel brakes use it up.

[Raptor9]

Not all helos with hydraulics in their flight-control servos require hydraulics to fly them in an emergency.  Some helos do, especially larger/heavier helos, and losing hydraulics will result in the controls locking up.  Other helos can still be flown with great effort and less stability.

 

Having said that, I have no idea what category the real-life Ka-50 falls into, but I would assume it would fall in the former due to it's size and weight.

[Reticuli]

That's true on aircraft where there's direct connections between the inputs & control surfaces and the hydraulics are then supplementing alongside.   If I recall correctly, the A-10 doesn't need its hydraulics.  Even in aircraft that can't continue flying much without the hydraulics, they're not usually out immediately and it's still often a gradual reduction of pressure up until that tipping point occurs when it drops rapidly.  This is the case in both hydraulic fluid leaks and pump failures.  I have no idea what happens with fluid contamination, but I don't think sims need to model every scenario and subsystem in order do a fairly-convincing and interesting recreation of such failures. 
 

The sim currently certainly registers 'hydraulics damage', right?  So just have the hydraulics pressure drop faster as a result of rough handling.  90% of normal pressure could even equal 90% cyclic control authority.  The cyclic at any deflection away from center would have a slight reduction rate % of pressure over time... because it's cyclical and requires some hydraulics work to keep doing its thing.  You then get a certain reduction % of pressure for each swing of any control axis from one extreme to another (-1 to 1 or vice versa) and it's a linear fraction of that when less.  I think they could start in testing with every full opposing swing being just a direct 2% reduction (1 - -1) and then let the fractions be just linear proportional.  Let's ignore the Y aspect trig for a moment and just look at one axis:  you move from X as -0.2 to 0.1 and you've just instantaneously dropped 0.3% further pressure over that other default rate that's occurring in the background from just having the cyclic off center.  That default rate could be as simple as like 1% of the trig distance the cyclic is from its center per second or something, so a max of 1% of 1%-ish per second or max of 0.01%/sec or 6% loss in 10 minutes if the cyclic was full forward.  So you have this slow cyclic positional loss and the aforementioned loss from being dynamic on any of the controls.  I have no idea if these values are too high or low, but I'm sure ED would quickly figure out if they need double or half or something to make it reasonably-playable for a while if you're gentle.  If their current damage tracking is based on values, that could figure into it.  You have a high damage value hit on this system, the losses could be greater and faster than a lower damage hit. 
 

Now, the 'control authority' in this sense I would think would be absolute cyclic position, such that degraded authority in the cyclic is defined as inputs resulting in less translated actual cyclic influence on the main rotor for a given input as if you didn't deflect as far as you think, and in the case of collective or pedals degraded authority would be less dynamism such that it's correspondingly slower to respond to the changes you make.  If the real shark can't do much when it's out of pressure, then when it runs out I hope you're on a good glide into a safe landing and the gear is already down.  The cyclic I'd assume would behave like it was centered (not necessarily a good thing) and I presume you'd just have the collective and pedals' influence frozen in their current position.

Edited June 16, 2021 by Reticuli

[AlphaOneSix]

The hydraulic systems are far more binary than that. They will work 100% effectively until they run out of fluid (in the case of a fluid leak) or the accumulator is empty (in the case of a pump failure), at which point they go straight to 0% effective. There is no point where they work "a little bit". Wherever the controls happen to be when this happens is where they will stay.

 

The switchover from the main hydraulic system to the common hydraulic system for the flight controls is automatic. So if you lose the main system, the common system can power the flight controls 100% effectively as long as the common system continues to function. This can be tested by turning off the main hydraulic system and seeing that the common system valves open. If you lose the common hydraulic system and not the main system, there is no effect on the flight controls, since they weren't powering the flight controls anyway.

[Reticuli]

Ok.  If you want it that way there's no reason you still can't just have pressure drop from controls usage using the same math but instead do nothing with the controls authority part until pressure actually reaches zero and that's when controls authority disappears (not freezing your physical sim controls, obviously, but the red controls indicator box).  Or you could even start a short & rapid but still gradual controls authority degradation phase when the pressure finally reaches 10% remaining for just a brief period before it goes out completely... even less time to zero if you give into the temptation to really push them hard to compensate for the sudden loss of authority.

Nonetheless, I strongly suspect when you lose all authority the cyclic effect on the blades as they go around is not going to remain as it was but is going to go to an untrimmed & centered state as if nothing cyclical is happening anymore on the main rotor.  The long-pole cyclic in real life might freeze, but even if it froze in a skewed position, it seems like the loss of control on the main rotor should simply keep the current collective pitch state minus the cyclic portion... correct me if I'm wrong.  Doesn't the cyclical action require hydraulics pressure to occur at all or is this current cyclical pitch changing independent of the hydraulics as long as the pilot's input isn't changing the swash-plate angle?

Edited June 16, 2021 by Reticuli

[AlphaOneSix]

The swashplates have no ability to center themselves if there is no hydraulic pressure. They will just stay where they were when the servoactuators stopped moving them. After all, they are physically connected, the swashplate cannot move independently of the servoactuators. Likewise, the controls in the cockpit are physically connected to the servoacuators. So the cockpit controls will also lock up and become immovable.

 

Also, this thread is using percentages quite a bit, which I'm not sure is appropriate. The operating pressure of the hydraulic systems is 65-90 kg/cm2. The accumulators are probably pressurized with nitrogen to somewhere between 30 and 50 kg/cm2. So this means that once the pressure in the system drops to the level of the nitrogen precharge, the pressure should in the system would immediately drop to zero. For example, if the precharge is 50 kg/cm2, then once the system pressure dropped to 50 kg/cm2, it would just drop off immediately to zero. So you really only have from wherever the pressure was (somewhere between 65-90 kg/cm2), until it drops to 50 kg/cm2 before the system completely fails. I'm just using 50 as an example, it could be higher or lower...but at least 30. The Mi-8 precharge is 30-32 kg/cm2 and it's operating range is only 45-68 kg/cm2.

 

Finally this also assumes a complete failure of both the main and common hydraulic systems, as each is capable of operating the servoactuators completely fine by itself.

 

I think it's just a system that is not very deeply simulated and I very much doubt it's something that ED is looking to change. But I'm happy to talk about it all day long.

[Reticuli]

4 hours ago, AlphaOneSix said:

The swashplates have no ability to center themselves if there is no hydraulic pressure. They will just stay where they were when the servoactuators stopped moving them. After all, they are physically connected, the swashplate cannot move independently of the servoactuators. Likewise, the controls in the cockpit are physically connected to the servoacuators. So the cockpit controls will also lock up and become immovable.

 

Ok, that is very interesting.  So the cyclical main rotor action would completely freeze in orientation at zero pressure.  Thank you.

On the pressure vs percentages, that should only matter at the pressure gauges vs the full pressure.  Going by just a freeze of the pilot controls, it's for reducing the pressure and either how you drop some other set of values or convert it when it's shown on the gauge.  You're just trying to crudely reduce the shown pressure until control become degraded (including completely frozen) based on amount of pilot controls handling and/or other factors.

On the cliff being higher up and not directly related to controls usage (an 'other factor'), I don't see why that would be an issue, rather it means to me it's a bit faster and changes what's shown on those gauges when.  You have rough controls increasing pressure drop until that cliff point, and at the cliff point it drops off rapidly.  Still seems easily doable. 

As for the two separate hydraulics systems... you then need these pressure loss behaviors on each one separately, right, and then if both fail, that's when controls degrade, as you said if the mains is lost the common takes over automatically and if the common 'backup' is lost you're already on the mains?  So that would mean you have two hydraulics systems that potentially incur damage to them separately.  Each look they have their own separate gauges below the hydraulic valve lamps.

Edited June 16, 2021 by Reticuli

[AlphaOneSix]

4 hours ago, Reticuli said:

As for the two separate hydraulics systems... you then need these pressure loss behaviors on each one separately, right, and then if both fail, that's when controls degrade, as you said if the mains is lost the common takes over automatically and if the common 'backup' is lost you're already on the mains?  So that would mean you have two hydraulics systems that potentially incur damage to them separately.  Each look they have their own separate gauges below the hydraulic valve lamps.

 

Yes that's correct. When both systems are operating normally, the main system supplies pressure to the flight controls, while the common system supplies pressure to the cannon actuators, landing gear extension/retraction system, and the wheel brakes. If the main system fails, the common system automatically switches over to supply pressure to the flight controls (in addition to the cannon actuators, landing gear, and brakes). If the common system fails, the main system continues to supply pressure to the flight controls, the cannon is no longer movable, the landing gear still work but have to be manually switched over to use the main system, and the brakes continue to operate using pressure from their own separate accumulator, although this accumulator is no longer being refilled/pressurized (the pressure gauge for this accumulator is the third one from the left in the bank of hydraulic gauges).

 

The good news is that if both systems fail, your brakes will still work for a while. But then again, if both systems fail I would be checking the operation of the ejection seat, not the wheel brakes.

[dimitriov]

IRL from retex in french army if you loose hydraulics on a puma you land fast or you're gonna die, controls simply are extremely hard and piloting the helo will be impossible( 4 tons pressure). And a Puma weighs from half to minimal kamov weight. A puma has 2 independant hydraulic circuits though. It's already been done surprisingly easily on gazelles though (they actually didn't bother landing until rtb) but a gaz weighs 2 tons, not 10 and the rotor-head weight is not the same.

 

The huey comparison is pertinent as the rotor blades themselves weigh nearly half the helicopter. (steel) Which leads to it being impossible to steer without assistance. 

 

Being able to manually direct a huge coaxial system with 6 blades on which is attached a 10 tons piece of metal sounds weird to me too. But hey, won't complain, in its current status 80% times you get hit you loose your hydro...

 

So well... 

Edited June 19, 2021 by dimitriov

[HuggyBear]

With regard to the Huey, you can fly it all day without hydraulics.

One of the checks carried out during Maintenance Test Flights was to ensure that you could hover with hydraulics turned off.

 

The blades don't weigh anywhere near half the weight of the helicopter.

[Rogue Trooper]

On 6/21/2021 at 1:22 AM, HuggyBear said:

With regard to the Huey, you can fly it all day without hydraulics.

One of the checks carried out during Maintenance Test Flights was to ensure that you could hover with hydraulics turned off.

 

The blades don't weigh anywhere near half the weight of the helicopter.

The weight of the chopper is in the blades.

An empty chopper maybe, 6 fully kitted muscle men..... hmmm... maybe.

[HuggyBear]

I'm not sure what you mean here, sorry if I've mis-read your post.

 

I don't recall how much a Huey's blades weighed, but the Chinook's blades are around 300lbs each and they're of a similar construction while being much bigger.

 

With the empty weight of the Huey at around 5800lbs, those two blades make up a very small fraction of the helicopter's weight.

 

Or did you mean the weight of the flight-control system?

 

It's completely controllable at MAUW of 9500lbs.

 

I've flown for around 20 minutes back to the field with failed hydraulics in a heavy Huey. We carried out a run-on landing to the runway as that was SOP, but it was completely controllable and could have been brought to the hover.

[Rogue Trooper]

It is the entire weight of the airframe you need to man handle once hydraulics are lost. 

9500 lbs are 4309 kgs.

the kamov is more than double that at 9000 Kgs empty of external loads.

 

Lets see if you find that so easy when you experience it.

 

The Huey was a superb design at the right time, basic and simple to keep costs down, everything was just about right on the Huey when it came into the Vietnam war in the 1960s. I think once the MI-8 gets a full reboot, the Huey should be next.

 

Edited July 22, 2021 by Rogue Trooper

[HuggyBear]

Okay, think I understand you now.

I was only talking about the Huey as it seemed as if posts were claiming the Huey couldn't be flown without hyds.

No idea about the Shark, never sat in a real one and can't read Russian.

[Volk.]

IIRC Barundus mentioned the AH-64 you had about 2 seconds of stick input before it was practically immovable, while in the OH-58D you could still fly it without boost.

Boosted also mentioned the Blackhawk was mostly a no-go without hydraulics. Got it timestamped in a video, but they mentioned pressures etc.

But by gross speculation, I'd guess the Shark's accumulator should also run dry after some amount of input from collective/cyclic movements. I think only pressing the wheelbrake (but not the act of holding it) currently depletes it.