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Saab Hydraulics Pump - Confused

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Hi all,

 

I've just started flying the Saab and I've hit on a slightly confusing behaviour from the hydraulics, which doesn't seem to have an obvious answer (at least based on my reading of the Systems manual).

 

For my first few flights, the hydraulics pump would activate for a couple of seconds every few minutes and then switch off, this was irrespective of phase of flight or config, as long as I had started up it kept happening.  No warning lights were showing, and it didn't seem to have any effect, so I put it down to a quirk of the type (never having flown a real one).

 

On my last flight, it seemed that after startup, the hydraulics pump activated continually, again, irrespective of flap or gear actuation.  If I used the Hydraulic Pump switch and moved it to OVRD then back to AUTO, it would turn off, only to re-activate a minute or so later.  I was additionally getting Low Hyd Pressure warnings on the panel.  The only thing I could see that didn't look like the previous flights was that the Hyd Fluid quantity was slightly lower, but still in the middle of the green arc.

 

From the Systems Manual, the only things simulated that should influence this are wheel brakes, gear & flap actuation and the pump switch, but I've been following the checklists and given for the bulk of the flight the pump was on auto, gear was up, flaps were up and wheel brakes were off, I'm rather stumped as to what could be causing this.

 

Any thoughts?

 

Cheers,

 

Jamie

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Hi all,

 

I've just started flying the Saab and I've hit on a slightly confusing behaviour from the hydraulics, which doesn't seem to have an obvious answer (at least based on my reading of the Systems manual).

 

For my first few flights, the hydraulics pump would activate for a couple of seconds every few minutes and then switch off, this was irrespective of phase of flight or config, as long as I had started up it kept happening.  No warning lights were showing, and it didn't seem to have any effect, so I put it down to a quirk of the type (never having flown a real one).

 

On my last flight, it seemed that after startup, the hydraulics pump activated continually, again, irrespective of flap or gear actuation.  If I used the Hydraulic Pump switch and moved it to OVRD then back to AUTO, it would turn off, only to re-activate a minute or so later.  I was additionally getting Low Hyd Pressure warnings on the panel.  The only thing I could see that didn't look like the previous flights was that the Hyd Fluid quantity was slightly lower, but still in the middle of the green arc.

 

From the Systems Manual, the only things simulated that should influence this are wheel brakes, gear & flap actuation and the pump switch, but I've been following the checklists and given for the bulk of the flight the pump was on auto, gear was up, flaps were up and wheel brakes were off, I'm rather stumped as to what could be causing this.

 

Any thoughts?

 

Cheers,

 

Jamie

Jamie,

 

In addition to the items you mentioned, we have modeled "leakage" in the hydraulic system.  Over time the hydraulic pressure will diminish and the pressure switch will activate causing the pump to re-charge the accumulators.  We also track how long it has been since you last used the Saab in X-Plane and then calculate the leakage accordingly.  So, if you load the Saab after a long period of time the hydraulic system will leak and the pressure will diminish.  If you load the Saab after only a short period of time, the pump should not run as the system will not have leaked enough.  

 

The pump SHOULD NOT run continously unless you override it.  If that happens please report back with all the details to recreate the issue and I will investigate.

Edited by JGregory
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Jamie,

 

In addition to the items you mentioned, we have modeled "leakage" in the hydraulic system.  Over time the hydraulic pressure will diminish and the pressure switch will activate causing the pump to re-charge the accumulators.  We also track how long it has been since you last used the Saab in X-Plane and then calculate the leakage accordingly.  So, if you load the Saab after a long period of time the hydraulic system will leak and the pressure will diminish.  If you load the Saab after only a short period of time, the pump should not run as the system will not have leaked enough.  

 

The pump SHOULD NOT run continously unless you override it.  If that happens please report back with all the details to recreate the issue and I will investigate.

 

Hi Jim,

 

Thanks for the prompt response  :)

 

To clarify about leakage, would this just impact at the start or do you simulate leakage during the flight?  If the latter, that would explain the occasional pump activation throughout the flight.  I've only had the Saab 3 days and have flown it each day, so I wouldn't expect a huge amount of leakage between flights (it's not a rusty Ford I assume?).

 

On the second point, yesterday it was definitely activated the whole flight (except when specifically turned off).  I'll try recreate it again tonight, what sort of info would you regard as "all the details"?  Just want to be sure that I give you the right information the first time!  :lol: 

 

Cheers,

 

Jamie

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Jamie,

 

Yes, the hydraulic system leaks continuously, even during flight.  We had three real-world Saab 340 captains as consultants on this project, and they all confirmed that the system leaks to the point that the pump will run 2-3 times per hour.  Keep in mind that the amount of fluid lost does not have to be significant to have the pressure drop to the point of tripping the pressure switch.

 

As to the "details" when recreating the problem... it is very helpful to know what steps you took just prior to the issue occurring. ie. does this only occur on the first flight?, Was the Saab loaded when the sim was first loaded, or was there another aircraft loaded first?.  Does this only occur after takeoff, or only in flight?, Were the flaps extended or "in the process of extending? (same for the gear).  Situations and circumstances that are repeatable to create the problem are what we are looking for.

Edited by JGregory

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Interesting. So if we haven't flown the SAAB for a while and the Hydraulics have been leaking, how do we fix this before a flight? How do we reset the system?

Sent from my iPhone using Tapatalk

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Interesting. So if we haven't flown the SAAB for a while and the Hydraulics have been leaking, how do we fix this before a flight? How do we reset the system?

Sent from my iPhone using Tapatalk

You don't have to do anything.  Once the Saab has power, the hydraulic pump will run and bring the pressure back up to normal.

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Ok thanks, so the actual quantity is not modelled?  In other words, it leaks but the quantity never diminishes?  I don't mind, just trying to understand how far it is simulated

 

Can't stop flying this thing!

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In other words, it leaks but the quantity never diminishes?  I don't mind, just trying to understand how far it is simulated
The quantity will not go to zero when the aircraft is not loaded.  We didn't want to force the user to have to use "virtual" oil cans and refill the system after a long layoff :)  

 

Note:  Technically, hydraulic oil is virtually uncompressible, unlike pneumatics.  So, it only takes a small leak (very little oil volume) to reduce the pressure significantly.  In addition, once the system is de-pressurized, you have less of a leak or maybe none at all!  Completely draining the oil supply is unlikely and therefore not something we modeled.

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Flying today, the pump is activating every 20 seconds or so. The system leaks noticably, and when the needle reaches the bottom of the green arc, pump activates and brings the pressure to about half way of the green arc. Surely this is not normal behavior? I had to disable the sound in cruise because it is driving me insane! It started right after powerup and has continued to cruise. 

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Taken from an email I received from 1 of the pilots with regards to this very thing.  I asked him what the frequent, high pitched whine was in 1 of the videos I got from him.

"That's the Saab mating call.
It's the hydraulic pump kicking on because he's using nose wheel steering and brakes.
Pressure dropped below 2100psi on Main Accumulator with Hydraulic Pump Switch in Auto Mode. Shuts off at 2900psi.
I remembered a bunch of Saabs parked out on the ramp with external power plugged in and they would "talk" to each other."
 
Followed by:
"The hydraulic pump comes on any time with external power or 28v generators operating, or in Override. 
Frequency of it coming on depended on how "leaky" system was. On ground with engines off and external power plugged in, the pump would come on about every 10-20 minutes. Comes on during every aircraft power up if it sat for a while. 
I imagine that would be interesting to simulate. Pressure cycling below 2100psi every 20 min on ground and higher frequency with more hydraulic usage."
 
Can you confirm the time is actually 20 seconds, or is it actually longer?  I ran the Saab on my installation, and it is nowhere near 20 second intervals between hydraulic pressurizations.  If it IS 20 seconds between pressurization, then that would be a serious issue that we would need to look into.
Edited by Goran_M
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It might not have been exactly 20 seconds but definitely less than a minute intervals. I have also noticed, that on the ground wind tends to move the Saab's rudder and pedals. It is a slightly weird behavior but I guess plausible... I don't know if it is normal, if there is a connection or if it is noteworthy but worth a mention. I will do another flight today and see if anything is changed / measure the intervals if it is important. 

 

//Today, without any rudder movement the interval is exactly 65 seconds. Don't really know how to completely "reset" the aircraft without a reinstall?

Edited by heinz92

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Steering, flaps, and brakes are the main hydraulic consumers.  With the plane sitting on the ramp and not moving, the pump SHOULD NOT cycle every 65 seconds.  Re-installing the aircraft would not change this.  What version are you using?

 

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Version 1.3. Using XP 10.45. Tried reinstalling, obviously no help. Tried loading a default Cessna, then the Saab, still the same results. Tried it on a Cargo and a Pax version. Hydraulics system is still leaking considerably while on the ground. Uploading a log file. 

Just to confirm, is it normal to sometimes see quite violent rudder movement, I'm presuming caused by wind? Its not really smooth, but quite firm. Doesn't happen all the time though and hydraulics system leaks regardless. Log.txt

Edited by heinz92

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I had a situation where the pump would not stop running.  I had to switch it to manual and operate it when the level dropped.  That was quite some time ago and the current version, just thought it was a programmed "glitch".  Last time I flew I disabled the autopilot and the warning chime never stopped until engine shutdown.  That may have had something to do with enabling using the default XP mapped switch and then also flicking in on with the mouse and then disabling it with the mouse...not sure.  You guys must hate us.

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5 hours ago, heinz92 said:

Version 1.3. Using XP 10.45. Tried reinstalling, obviously no help. Tried loading a default Cessna, then the Saab, still the same results. Tried it on a Cargo and a Pax version. Hydraulics system is still leaking considerably while on the ground. Uploading a log file. 

Just to confirm, is it normal to sometimes see quite violent rudder movement, I'm presuming caused by wind? Its not really smooth, but quite firm. Doesn't happen all the time though and hydraulics system leaks regardless. Log.txt

First, are you using any hardware?  It may be possible that "noise" is causing the flaps or brakes to constantly activate, which may cause a higher rate of leakage.  Maybe try disconnecting your hardware and testing.  

Second, you have quite a few other plugins installed.  I would suggest you remove them and see if anything changes.  You can then put them back one at a time and see what happens.

Edited by JGregory

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I only have a simple joystick, nothing assigned for brakes and flaps but buttons. There's no visual evidence of any noise on any aircraft, but I will examine the controls closer. I've also encountered a situation when after powering up, immediately the pump activates and doesn't stop running. 

I will also remove every other plugin and report results tonight. 

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Removed plugins and controller and returned them, the issue seems to be gone for now. Raised the null-zones a little bit to remove any adverse effects from noise. Still encountered the issue where the pump wouldn't turn off after power-up, but a reload helped. 

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Hello. I'm a new member to this forum and interested in the simulated hydraulics system re saab 340a. 

I've understood all that has been said so far but there doesn't seem to be a resolution to the 'problem'.

Indeed, if there is a problem. I continue to experience all the above and find no other recourse but to turn

off the dedicated sound provided for the hydraulics pump alert signal. I was manually activating the pump

when needed (in flight, on the ground, pre/post start-up ...etc). The other thing noticed: the Hyd fluid level gage

was at the end of its arc (full). I apologize if this topic has been concluded else where but I can't seem to locate it.

cheers

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Further trouble shooting seems to suggest a conflict with my controller/config  etc ...

Toe brakes were coupled with rudder cmd ( can't seem to separate the two )  ...so ... everytime

a rudder command was issued the simulation would read it as a toe brake cmd as well ....

... thanks to JGregory for the suggestion.

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....further to the above observations ... it appears the saab reads the rudder cmd along w/ the tiller/nose wheel ( say in a twist joystick config)

and the hyd psi drops like a rock ( on the ground or in the air ...) 

...if i use only L/R brakes for navigating ground, the hyd psi will drop but at a much slower rate... there seems no way around this ...

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ok jim .... so .... i was able to separate t/brakes from the rudder on a twist/joystick (by coupling second joystick) and satisfied myself

that that was not the issue: i.o.w. hyd psi still dropped quickly regardless of t/brakes being isolated. I concluded the 'problem'

is in the  rudder/tiller pairing ...and i believe there is no way to separate the two. the effect is the same in the air as it is on the ground

i guess that's the problem: whenever one inputs on the rudder it is also read as a tiller input and psi drops dramatically.

when i deplete the hyd system of psi, flaps are lost but nothing else...interestingly i notice the tiller wheel left of the captain's seat

appears to do nothing altho' suggestions are made as tho' it should be functional.

...thoughts?

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Tiller is something we will be upgrading/modifying/?fixing? for the next update :)

I will look into the tiller/rudder pairing issue and discuss with Laminar if necessary.

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