Hydraulic systems

Operating an F-16 on the ground or in the air - from the engine start sequence, over replacing a wing, to aerial refueling procedures
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simonlwa

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Unread post24 May 2009, 19:05

slay0r wrote:Does that means I couldn't lower my landing gear when i flyin under EPU,since EPU can only provide pressure for System A?



Bro slay0r, I guess you might have overlooked some of the replies that others added. It is true that when the aircraft is running on EPU, we do not have the hyd pressure to lower the gears but remember we still have the alternate landing gears? It relies on Nitrogen as mentioned above so the falcon can still land with its landing gears.

Bro aim-120c5, to your question regarding the FFP. I guess its a safety feature that it is still important to have the falcon fuel system balance. Imagine the aircraft on EPU yet still fuel imbalance. The aircraft might crash due to lost of control because the aircraft CG is not balanced. agree?



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Simon
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slay0r

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Unread post24 May 2009, 20:13

simonlwa wrote:
slay0r wrote:Does that means I couldn't lower my landing gear when i flyin under EPU,since EPU can only provide pressure for System A?



Bro slay0r, I guess you might have overlooked some of the replies that others added. It is true that when the aircraft is running on EPU, we do not have the hyd pressure to lower the gears but remember we still have the alternate landing gears? It relies on Nitrogen as mentioned above so the falcon can still land with its landing gears.

Bro aim-120c5, to your question regarding the FFP. I guess its a safety feature that it is still important to have the falcon fuel system balance. Imagine the aircraft on EPU yet still fuel imbalance. The aircraft might crash due to lost of control because the aircraft CG is not balanced. agree?



Regards,
Simon


oh, U r right. NacyFalcon has alreay mentioned that ...I was staring at that Pic ...

BTW: What are those accummulators? They are not Nitrogen bottles, are they?

Abut EPU: Does EPU automatically kicking in as soon as engine stop working, or it has to be actived manually?
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simonlwa

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Unread post25 May 2009, 16:54

slay0r wrote:
simonlwa wrote:
slay0r wrote:Does that means I couldn't lower my landing gear when i flyin under EPU,since EPU can only provide pressure for System A?



Bro slay0r, I guess you might have overlooked some of the replies that others added. It is true that when the aircraft is running on EPU, we do not have the hyd pressure to lower the gears but remember we still have the alternate landing gears? It relies on Nitrogen as mentioned above so the falcon can still land with its landing gears.

Bro aim-120c5, to your question regarding the FFP. I guess its a safety feature that it is still important to have the falcon fuel system balance. Imagine the aircraft on EPU yet still fuel imbalance. The aircraft might crash due to lost of control because the aircraft CG is not balanced. agree?



Regards,
Simon


oh, U r right. NacyFalcon has alreay mentioned that ...I was staring at that Pic ...

BTW: What are those accummulators? They are not Nitrogen bottles, are they?

Abut EPU: Does EPU automatically kicking in as soon as engine stop working, or it has to be actived manually?


1) Ya,the accumulators are stored with Nitrogen,serviced to 3000psi.
2) EPU can be selected manually or automatically. Its discussed in some other threads.

a) When your main gen and standby gen both fails
b) When both your hyd sys pressure drops below 1000psi

i think there's still another condition for auto firing...i've got a bad memory haha....i gotta check it out.


Regards,
Simon
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dukey172

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Unread post26 May 2009, 13:33

You have your alt gear handle to blow the gear down. Nevermind didn't see the post that talks about this
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mikevh

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Unread post10 Jul 2009, 15:22

Does anyone have the hydraulic system test procedures for the F-16 when using a mule to validate operations? The hydraulic schematic posted is extremely valuable, but flow and pressure data would be quite valuable to configure a test stand.
Thanks
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abc123

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Unread post11 Jul 2009, 10:48

An accumulator isn't just a nitrogen reservior. An accumulator is a hollow cylinder with a moving piston in the middle. The piston seperates the cylinder into 2 sealed chambers. One end of the cylinder gets serviced with nitrogen, the other end is connected to the aircraft hydraulic system. The nitrogen is serviced with no hydraulic fluid in the cylinder, so the piston is bottomed out against the inside of the hydraulic end of the cylinder. The specific pressure to which you service the accumulator with nitrogen is refered to as the precharge. Precharge is always less than aircraft hydraulic system operating pressure. When hydraulic pressure is applied to the accumulator by the aircraft hydraulic system the piston is pushed back into the cylinder. This increases the pressure of the nitrogen charge until it becomes equal to the pressure of the aircraft hydraulic system. Some accumulators have check valves so they keep the hydraulic fluid inside, so even when hydraulic pressure drops to 0 the accumulator is still at 3000 psi. An accumulator's basic job is to store potential energy. In the event of a B sys hydraulic failure, application of the brakes causes hydraulic fluid from the JFS/brake accumulators to be ported into the brake system. The 2000 psi precharge is greater than that of the failed B system, so the precharge pushes fluid into the brakes. When the brakes are released the fluid flows into the B system return, so it's gone forever. Thus, once you lose the B system you still have brakes, just not for very long. Remember, the parking brake holds its pressure without releasing, so if you come to a complete stop and then set the parking brake you can sit there until the battery dies.
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abc123

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Unread post11 Jul 2009, 11:08

One more thing. I've been reading on here for years. VarkVet, you're a frigging bad a$$. You know technical info that no operator has a right to know. I've been hands on the jet for 9 years now, and you still throw out info that I didn't know sometimes. So, with the disclaimer aside...

Dumping the reservior accumulators to precharge is definately carded in the recovery. It's not just something we do. I don't know the card #, but it's in there. I can specifically recall showing it to a rookie who tried to talk his way off of my sh*t list. He didn't dump his accumulators, I busted him, and he said it wasn't his fault because he didn't preflight it yet. He was wrong. If it was something we just do because we like to do it people would be getting QA fails on recovery PEs for doing it. Plus, in my opinion, checking the reservoir accumulator precharge is a critical task. A bad reservoir accumulator precharge can lead to pump failure. It's gotta be carded

We don't memorize tech data, and I haven't done a recovery in about a year, so let me get my hands on a -6 and verify before the flames start...
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VarkVet

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Unread post11 Jul 2009, 20:19

abc123 wrote:We don't memorize tech data, and I haven't done a recovery in about a year, so let me get my hands on a -6 and verify before the flames start...


No flames, you are correct it’s in the 6WC (I’ll look it up as well)
Dumping the reservoir accumulators is one of those things that everyone just does! Sometimes your help dumps the system sooner than you want … especially when you need to bleed down “A” a bit. :lol:
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abc123

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Unread post11 Jul 2009, 20:40

This is way off of the OP's question, but I guess I don't get why it's "one of those things that everyone just does". It's in the -6. Nobody does things that are carded in the -6 just to do them. They do them because they're in the -6. We don't help the system dump, be it too soon or not, we dump it intentionally because we have to. It isn't going to do it on it's own unless it has a bad pressure relief valve, check valve, or dump valve. More often than not the system doesn't need to be bled according to the servicing charts until after it's dumped, so whoever dumps the system may not know he's shooting himself in the foot when he dumps it. That's why some of the more experienced guys will burp their hydraulic systems before dumping them even if they don't appear to need it. It'll release any trapped nitrogen from the reservoir if it's in there, and if there isn't any it won't drop the servicing more than a percent or 2, so there's no harm. Top it off once every few days and rock on.

Anyhow...way OT. My apologies to the OP.
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VarkVet

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Unread post12 Jul 2009, 00:02

abc123 wrote:This is way off of the OP's question, but I guess I don't get why it's "one of those things that everyone just does". It's in the -6. Nobody does things that are carded in the -6 just to do them. They do them because they're in the -6. We don't help the system dump, be it too soon or not, we dump it intentionally because we have to. It isn't going to do it on it's own unless it has a bad pressure relief valve, check valve, or dump valve. More often than not the system doesn't need to be bled according to the servicing charts until after it's dumped, so whoever dumps the system may not know he's shooting himself in the foot when he dumps it. That's why some of the more experienced guys will burp their hydraulic systems before dumping them even if they don't appear to need it. It'll release any trapped nitrogen from the reservoir if it's in there, and if there isn't any it won't drop the servicing more than a percent or 2, so there's no harm. Top it off once every few days and rock on.
Anyhow...way OT. My apologies to the OP.


Flame-on

Ya, like I said I’ll look it up.
The system is dumped to pre-charge regardless and reservoir accumulator pressure will not build to 3000psi if pre-charge is low. Something we look for on Launch. (Most important)

Doesn’t make sense to dump pressure on recovery, as system pressure to suction of the pumps is a bonus in my opinion if you have multiple flights. (But it’s done) Like I said I’ll look it up … T.O. change may be in order? (Less important)

I’m actually embarrassed because I can’t recall (right now) what section of the 6WC deck it actually tells you to dump the reservoir accumulator, but I know it’s in there, I know it has to be done, and I know when I build my routine to turn a jet within an hour, it will get done!

a. 6WC specifically states you can have help doing a thru flight but CC signs off the entire inspection
b. Please don’t preach T.O. (-6) usage because we all use them … I can’t control others when I’m down the tube, I just have to trust my collogues and assume they know what they’re doing or better communication process from me!

More on Pneudraulics
You know your system is sweet when it’s in range pressurized and un-pressurized especially when you work in an area that has a vast 40-50 degree temperature split during the summer. No need to burp it after every flight? She’s not an F- 4

Viper has a very, very good hydraulic system and other notes.
a.Only pumps I’ve ever replaced were for time change requirements. No cavitation issues, seen one or two case drain DPI’s popped! Never flushed a Viper due to a catastrophic pump failure … do dah, do, dah
b.I’ve seen numerous Code one Vipers return from flight with so much air, fluid vented out of overflow upon dump. (normally bad JFS accumulator) {IF IT WAS AN F-111 SHE BE VERY SQUIRLLY to fly} In matter of fact Lakenheath almost lost one when the pilot had to blow the gear down and the pneumatic pressure by-passed the shuttle valve in the nose gear down actuator and filled Utility with Air!
c.Have you noticed the plaquard change for reservoir temperatures on the F-16? (After 30 years, now a problem and an increase?)
d.I’ve got 7 years on the Viper, and for a jet that’s been around for so long, I am amazed at some of the T.O. errors and how week the FI’s are?
e.Yup, the Viper shouldn’t be a crew chiefs first jet because you’re going to get spoiled!

I don’t TEXT message so it took me a while to figure out OP and OT … I much sooner pick up the phone and talk to someone.
TPWWOT (this post was way off topic) AIDGAS (and I don’t give a sh*t)
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abc123

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Unread post12 Jul 2009, 12:21

VarkVet wrote:Flame-on


:?

Really? I'm just asking why you'd say it's just something people do when it's actually a carded item. That's like saying some crew chiefs like to do intake inspections because it's just something they do. Nobody's preaching. You don't have to get all defensive. Everybody knows you know your business. Sheesh... And why would you be embarassed that you can't recall specifically where it's carded? You're not supposed to be able to recall, you're supposed to look it up everytime. At least, the crew chiefs are supposed to. Maybe you are supposed to know for whatever job you have right now. Still, I'm not embarassed that I can't recall.

Since you brought it up, yes it does make sense to dump the reservoir accumulators on every recovery. You said yourself, with a low precharge it won't properly build pressure. It needs to be checked for proper precharge prior to every single flight. The variable volume pumps come up to pressure and begin pressurizing the reservoir accumulators waaaay before there's a volume demand high enough to worry about cavitation.

Yes, the system is sweet when it's within the correct pressure range both pressurized and unpressurized, but this isn't always the case. Theories of operation are cool, but most of the jets I've crewed must have forgotten to read their GS. Burping the system is harmless, and it can save you having to hook up a mule on a thruflight. Ultimately, this is an indication of an accumulator that's failing, and it needs to be fixed, but it's not worth breaking a good flyer if you can manage it with the occasional burp.

I have flushed an F-16 following catastrophic pump failure, I have seen a broken input spline, I've replaced pumps for improper pressure output (high and low), and I've replaced pumps for howling (cavitation). Still, I've done maybe a dozen bad pumps versus 30-40 removed for time change or TCTO.

And I don't text either, I think it looks silly. Plus my thumbs are too fat. :D
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NANCYFALCON

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Unread post28 Jul 2009, 19:36

slay0r wrote:Does that means I couldn't lower my landing gear when i flyin under EPU,since EPU can only provide pressure for System A?


The landing gear can always be lowered because it has a back-up system that works on nitrogen. It is initiated in the cockpit with the "alternate gear" handle which actuates a valve which passes nitrogen from the Alt gear/Arr Hook reservoir to the required components to unlock the landing gear components.
There is a procedure described in the Job Guide for getting the nitrogen out of the system (Bleed and leak following pneumatic extension) and resetting the position of the shuttle valves and landing gear selector valve, so normal hydraulic operation of the landing gear can be used again (this procedure is also being done after ldg components replacement).

That is how it's works in a nutshell, hope it's useful for you.
Regards, Nancy
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VarkVet

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Unread post02 Aug 2009, 13:04

As posted before … precharge is checked during BPO/PRE and WAI only.


Also if your blow down bottle doesn’t hold and you leak-detected all the way down the system … check out the Alt Gear/ Hook control valve!
I cracked the line going to the hook and was getting bubbles with leak-tek … changed the valve and all is well.
My supervisor said that in over 26 years working the F-16, he never seen that valve changed!
Also WARNING in TO not pull hook pin if under tension … now you know why!
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That_Engine_Guy

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Unread post02 Aug 2009, 14:08

VarkVet wrote:My supervisor said that in over 26 years working the F-16, he never seen that valve changed!


Valves, lines, harnesses...

Seems like the older they get the more "never seen that" situations we're having...

:cheers: TEG
[Airplanes are] near perfect, all they lack is the ability to forgive.
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VarkVet

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Unread post02 Aug 2009, 14:19

That_Engine_Guy wrote:
VarkVet wrote:My supervisor said that in over 26 years working the F-16, he never seen that valve changed!


Valves, lines, harnesses...

Seems like the older they get the more "never seen that" situations we're having...

:cheers: TEG


Ya, but that was on a '92 block 15?
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