FSXA Auxiliary hydraulic system (SOLVED)

#1
Since i am working with a jet the hydraulics only work with engines running.
Has anyone found a way to create an auxiliary system so there is a small amount of hydraulics before the engines are running?

Is there a table i can add to my air file to bypass engine state?
 
#3
Thanks for letting me know you can't add a section in the air file.

Well there is no electric hydraulic there is only electric. Which would then not respond to my auxiliary hydraulic switch and then when engines are running we would want even more hydraulic pressure indicated on the gauge. And this would be a very challenging re write to make this all work. I already have a GPU but again i think i will just let the engines produce hydraulic power.

Although in my other aircraft non jet you can get hydraulic pressure before the engines are running. And so i figure it's the air file that can be altered to get this result. This would be the way to make both auxiliary and engine hydraulic systems work.
 

Roy Holmes

Resource contributor
#4
Not that I have ever used it, but there is a standby electric pump for hydraulics as well as the possibility for hydraulic pressure to be generated electrically. If I did not know that I would never have suggested it.
Look carefully through this thread http://www.fsdeveloper.com/forum/th...-vc-but-not-in-2d-cockpit.250414/#post-432229
There is an event HYDRAULIC_SWITCH_TOGGLE which can address engine or standby hydraulic power and a variable CIRCUIT HYDRAULIC PUMP ON, Bool "Is electrical power available to this circuit"
So if you have a GPU which generates electrical power on the ground, you can turn on an electric hydraulic pump.
Two hydraulic pumps operating in parallel at 3000 PSI produce 3000PSI pressure, not 6000.

The air file has a series of records dedicated to generating readings for engine instruments, but both jet and piston files do not (in the latest version) include hydraulic pressure.
Record 514, which is UNUSED, was a table of hydraulic pressure.
Hydraulic pressure is a function of engine RPM and the values used in the aircraft.cfg. With an electric pump it would be a function of whether it is switched on and the same pressure value in the .cfg.
Roy
 

Heretic

Resource contributor
#5
I know that you can set up two separate hydraulic systems that are monitored with "(A:HYDRAULIC PRESSURE:index, psi)" and controlled with "index (>K:HYDRAULIC_SWITCH_TOGGLE)" (see Roy's link).

You could try to set up two engine-driven systems in the aircraft.cfg with engine_map=1,1,0,0 and see if the electric_pumps line accepts more than a simple "1" and "0" as values, maybe something like the engine map for the pumps, to set up an electrically powered system.

If this doesn't work either and you absolutely need an auxiliary system, you'll have power the default hydraulics with electric pumps and then put your custom system's code, including pressure simulation and effect on flight controls, gear, flaps, etc...on top of it.
 
#6
I will do some testing tonight. I also wanted to correct a statement i posted above that i said "non jet you can get hydraulic pressure before the engines are running" when using standard setup. My other aircraft also need the engine running. And i was wrong saying there is no electric hydraulic pumps.
 
#7
I see this is interesting....

1 is for toggle the first engine hydraulic pump
2 is for toggle the second engine hydraulic pump
3 is for toggle the backup electric hydraulic pump

Now we might get something here if this in fact works.
 
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#8
The above did not work.

I noticed the flaps are still working with the cfg set to = 0 for no electric pumps. But the flaps move really slow. So for some reason i wonder if this is a built in auxiliary pump. Anyone ever seen this?

Using electric pumps solves my issue but now my custom HYD SW must be a dummy switch because the sims voltage controls when the "CIRCUIT HYDRAULIC PUMP ON" is active.

Can we create a code to override this variable?
 
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Heretic

Resource contributor
#9
I think your aircraft spawns with residual pressure in the hydraulic system. It's been a while, but when I tested this, I could command 100% flaps, but get an actual movement of maybe 50% before it ceased.

Read again what I posted in #5. You can very well code your own hydraulic system as long as you keep the default system working underneath.
 

Roy Holmes

Resource contributor
#10
Like Bill says "The SDK is worth reading" Well, maybe he never said those very words, but that was the idea.

I read through the electrical and hydraulic sections of "Aircraft Configuration Files" this morning and am including them below for y'all. Darn, 27 years of living in the States is finally getting at me!

[electrical]
These parameters configure the characteristics of the aircraft's electrical system and its components. Each aircraft has a battery as well as an alternator or generator for each engine.
Below is a table of electrical section parameters shown with default values for Bus Type, Max Amp Load and Min Voltage (the values applied if the parameters are omitted). The default Min Voltage equals 0.7*Max Battery Voltage. The list of components also reflects all of the systems currently linked to the electrical system. If a component is included in the list but the aircraft does not actually have that system, the component is simply ignored.

hydraulic_pump Bus type, max amp, min voltage (This is one of the list of electrical stuff).



[hydraulic_system]
The following parameters define the aircraft's hydraulic system:

Property Description Examples
normal_pressure The normal operating pressure of the hydraulic system, in pounds per square inch. Beech Baron 58( normal_pressure = 0.0 ) DeHavilland Beaver DHC2( normal_pressure = 1000.0 )
electric_pumps The number of electric hydraulic pumps the aircraft is configured with. Beech King Air 350( electric_pumps = 0 )

engine_map This array of positive integers sets the number of hydraulic pumps on the corresponding engines of the aircraft. The values correspond to the order of the engines, starting with the left-most engine first and moving right. By default, all engines are not equipped with any hydraulic pumps. DeHavilland Beaver DHC2( engine_map = 1 )
backup_reserve This system includes a backup reservoir for use after primary pumps have failed. ( backup_reserve = 1 )
max_reservoir_pressure_efficiency The approximate level in which the pumps will maintain the reservoir level. Set to 1.0 if a perfect system is desired. ( max_reservoir_pressure_efficiency = 0.98 )
min_pct_rpm_for_max_pressure The percentage of maximum engine RPM that engine driven hydraulic pumps will achieve 100% of normal pressure. The pressure will ramp up linearly. Omission of this constant will result in use of an internal mapping of RPM to pressure. ( min_pct_rpm_for_max_pressure = 0.2 )

So this is the place to state how many electrical hydraulic pumps there are. I have never flown with electrical hydraulic pumps, just ones driven by a gearbox from the engines, but I know the B737 has two electrical pumps in addition to two mechanical ones. Having a reservoir also explains the slow flaps with engine off movement that DG saw (and Heretics "residual pressure")

Like the man said "The SDK is worth reading". I had never studied those two sections in any detail.
Roy
 
#11
That explains why the flaps will still function with everything off as in my test window i do show max_reservoir_pressure_efficiency = 0.98. But since this never lowers i was not sure it came from this pressure. This is good to know in case of total failure.

From my testing i found using:

electric pumps 1
engine map 1,1,0,0

Allows the battery voltage to supply the electric pump and once the engines are running then the main hydraulic pressure takes over.
But when i tried to figure out a way to make a LVAR control the electric pump it fails as the voltage seems to be the only source to the electric hydraulic bus.
But i am going to try a few more things tonight.

"hydraulic_pump" hydraulic_pump Bus type, max amp, min voltage
Does not appear anywhere in the variables or event ID's.
 
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#12
SOLVED!
From my new testing i found using:

normal pressure 875.0
electric pumps 2
engine map 0,0,0,0

Allows my custom switch to control if hydraulic pump 1 will pressure up to 875 psi or if the switch is off and engine 1 running will also produce 875 psi.

Code:
(L:SW_HYD, Bool) 1 == (A:ENG N1 RPM:1, Percent) 20 > or (A:HYDRAULIC SWITCH:1, Bool) 0 == and if{ 1 (>K:HYDRAULIC_SWITCH_TOGGLE) }
(L:SW_HYD, Bool) 0 == (A:ENG N1 RPM:1, Percent) 20 < and (A:HYDRAULIC SWITCH:1, Bool) 1 == and if{ 1 (>K:HYDRAULIC_SWITCH_TOGGLE) }
Allows engine 2 to also produce 875 psi. So with both engines running you get a total of 1,750 psi.
Code:
(A:ENG N1 RPM:2, Percent) 20 > (A:HYDRAULIC SWITCH:2, Bool) 0 == and if{ 2 (>K:HYDRAULIC_SWITCH_TOGGLE) }
(A:ENG N1 RPM:2, Percent) 20 < (A:HYDRAULIC SWITCH:2, Bool) 1 == and if{ 2 (>K:HYDRAULIC_SWITCH_TOGGLE) }
Using 2 pumps in the cfg and no engine maps solved the issue for a custom setup. With the custom hyd switch off engines off and battery voltage the flaps will move very slow from the emergency reserve pressure.

I can now say the system works exactly like the real aircraft and i managed to come up with a solution that gave me exactly what i wanted. :yikes:

As usual lot's of testing came to the rescue. I do appreciate everyone for trying to help me on this issue but it came down to working long hours and trying different values to succeed.
I am glad i tried 2 pumps and no maps as this was the key!


 
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#13
I know of no hydraulic system that is 'additive'. Are you certain regarding the pressure level doubling with both pumps active?
 

Roy Holmes

Resource contributor
#14
"hydraulic_pump" hydraulic_pump Bus type, max amp, min voltage
Does not appear anywhere in the variables or event ID's.
Quite true, they are in the aircraft.cfg file which is what I was talking about.

Since your engine map is 0,0,0,0 neither of your engines are producing hydraulic power. See the excerpt from post 10:
"engine_map This array of positive integers sets the number of hydraulic pumps on the corresponding engines of the aircraft. The values correspond to the order of the engines, starting with the left-most engine first and moving right. By default, all engines are not equipped with any hydraulic pumps."
What is happening is that you have coded the electric pumps to operate when the engines are above idle.

You have not told us what aircraft you are modeling, but usually the electric pumps would be a back-up for engine driven pumps. As such, they would be connected to the hydraulic system in parallel with or in separate lines from the engine pumps. That means they would not be affected by a leaking system or seized engine driven pump. This is necessary to give the required system integrity and extremely low total failure probability (in the region of 1E-9 per flight hour). In parallel, as opposed to being in series, means the pressures are not "additive" as WarpD said. You would not want a back-up system to double hydraulic pressure for several reasons, like increasing the size of leak and not being at the normal operating pressure.

It may be that the sim does add pressures, but if so that is unrealistic.
Roy
 
#15
I know of no hydraulic system that is 'additive'. Are you certain regarding the pressure level doubling with both pumps active?
Well if your using 2 pumps the sim supplies pressure for each pump. So i have created my gauge to add them as a total. This way the auxiliary pump will use pump 1 for low pressure and when the engines are running you have high pressure.

So yes the sim hydraulic's is additive if your gauge uses variables including each pump. I was glad to see it does as i needed low and high pressure.

Quite true, they are in the aircraft.cfg file which is what I was talking about.

Since your engine map is 0,0,0,0 neither of your engines are producing hydraulic power. See the excerpt from post 10:
"engine_map This array of positive integers sets the number of hydraulic pumps on the corresponding engines of the aircraft. The values correspond to the order of the engines, starting with the left-most engine first and moving right. By default, all engines are not equipped with any hydraulic pumps."
What is happening is that you have coded the electric pumps to operate when the engines are above idle.

You have not told us what aircraft you are modeling, but usually the electric pumps would be a back-up for engine driven pumps. As such, they would be connected to the hydraulic system in parallel with or in separate lines from the engine pumps. That means they would not be affected by a leaking system or seized engine driven pump. This is necessary to give the required system integrity and extremely low total failure probability (in the region of 1E-9 per flight hour). In parallel, as opposed to being in series, means the pressures are not "additive" as WarpD said. You would not want a back-up system to double hydraulic pressure for several reasons, like increasing the size of leak and not being at the normal operating pressure.

It may be that the sim does add pressures, but if so that is unrealistic.
Roy
I know that the engines are not supplying pressure if i use engine map 0,0,0,0 but this makes the system work exactly how i need it. Is there a downside, yes. Electrical failures would be one. And if you have the generators off and no electrical then you have no hydraulics. But i think a hydraulic failure will still fail the system regardless of electric or engine driven. So this seems to be ok for the route i have gone.

It's a Learjet 35A. And customers want the working auxiliary hydraulics. I prefer to use electric with engine 1,1,0,0 mapping but then the battery controls the circuit for the electric pumps. No way around this. If there is i am all ears. But all my tests showed this was the closest way to produce a working auxiliary with low hyd pressure and full pressure when engines are running.
 
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#16
Just a single engine running should provide full pressure... your approach doesn't do that.

If you're saying the system should have 50% of nominal pressure with just an electric pump... that's one thing. But in no way is the system 'additive'. The system's pressure is either the low value or the high value... based on what's running. Electric pump: low value. Either or both engines running: high value.
 

Roy Holmes

Resource contributor
#17
LEAR 30 series hydraulics_75%.jpg

This is the LEAR 30 Series hydraulics system. Look at the yellow blob, which is the hydraulic reservoir. It feeds the engine driven pumps (boxes with figure 8 in them) and a separate 0.4 gal reservoir feeds the electric pump (with its ON/OFF switch). It does not say what the electric pump pressure is, but it does say it can only be run for 3 minutes then needs 20 minutes to cool down. There is a check valve in the main feed line to the left of the spoilers section, so the electric pump can only supply brakes, gear and flaps. You can see that all three pumps operate in parallel so their pressures are not additive. For the pressures to be additive, the output from one pump would have to go in the input of another, that is they would have to be in series. Normal pressure is below about 1700 PSI.

The flight control system on the Lear is manual so the hydraulic system does not need the very low probability of failure I mentioned earlier. There is emergency pneumatic pressure in the event of a total hydraulic failure.
I believe the electric pump would only be used for ground checks or in the event of a both engine pumps failing and the pilot did not want to fill the hydraulic lines with air.
Roy
 
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#18
Just a single engine running should provide full pressure... your approach doesn't do that.

If you're saying the system should have 50% of nominal pressure with just an electric pump... that's one thing. But in no way is the system 'additive'. The system's pressure is either the low value or the high value... based on what's running. Electric pump: low value. Either or both engines running: high value.
Yes if engines are off and you want to do ground checks then the pressure would be low pressure and the annunciator LOW HYD lights will be on. So this is why i made the gauge additive with 2 pumps. And to get the system the way the real Lear works just like Roy's post above which i already am aware of.

So with the code i wrote above the switch can stay off and based on the engines rpm and the electric pumps will run as if they were hydraulic. And with engines off we can still do ground checks. Or if there is a hydraulic failure you can use the electric pump as a backup. And yes it's the same 3 minute max or it will overheat.

So instead of putting
normal_pressure = 1750.0
I use
normal_pressure = 875.0
And if you use 2 pumps then the system is indeed additive as my gauge which uses 2 pump variables seems to read both and show 875 with 1 pump running and 1750 with 2 pumps running.

If you use a variable that just read hydraulic pressure then you would need to use
normal_pressure = 1750.0
to get this value.

So this is additive right?
 
#19
No it's not additive... you're the one adding it. We're telling you that a hydraulics system doesn't work that way. The pumps work in parallel and thus the pressure you would actually read for the system would be the highest pressure value. The sim's variables are like taking a direct read of the pressure off the physical pumps.

If all pumps are on... the pressure in the system would be 875, not 1750. I also can find nothing in the schematic above that indicates the electric pump runs at 50% pressure of the engine pumps. Also based on the schematic... electric pump would power everything except the spoilers. There also appears to be a pressure switch that will trigger the electric pump to run if system pressure drops below a certain value. Thrust reversers may or may not work one time after loss of hydraulics, depending on what reversers are installed on the aircraft.
 
#20
Aircraft hydraulic systems have accumulors. A fully pressured system will retain its pressure even when the pumps are turned off.
 
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