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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Chandawg

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Unread post03 Aug 2009, 01:06

I remember getting a field service report, stating that dumping the hydraulics on thuflights/recovery was causing problems for the hydraulic systems, something about the dump valves not lasting as long as they should. If you are getting constantly air (high servicing readings) in your hydraulics, it isn't always the accumulator for that system, it might not even be a whole lot of air, it could be pressure bleeding off of your JFS system to your B system, most of the time I have seen the B system reservoir close to 100%, its usually a good idea to check you JFS pressure and see if it has decreased, if you follow the Fault code for inaccurate reading of your reservoir or it actually increasing in quantity, it will have you change the reservoir and or applicable accumulator, but if you follow the Fault code for JFS loosing pressure over the course of 3 hours, it will take you through a series of checks, and towards the end have you change the solenoid valves, out of about 15 times of troubleshooting this problem, 12-13 have been those pesky start solenoid valves. They start to loose their magnetism over time and will seep open while power isn't applied allowing your JFS pressure to bleed into your B system and thus giving you the inaccurate quanity, and if they just get so bad that they won't close at all, your bottles won't even re-charge. Like I said, it is one of the last things in that Fault tree, and the Hi hydraulics is just a symptom of another fault, leading a lot of technicians to chase a ghost, like thinking their A system is always bleeding over into their B system hydraulics, cause they are constantly servicing A and bleeding B. It also has cause numerous hydraulic servicing during engine runs, because you check your hydraulics before the aircrew comes out and b is a little high, after engine start you have like 10 percent.....and unfortunatley I have seen it cavitate a pump, on landing roll the pilot reported his B system pressure dropped to below 1000 psi, and may have actually went to 0 but it came right back not taking any chances he shut down at the EOR, if that happens you change the pump. I submitted a change while I was at Nellis, but was denied by QA (really isn't their decision) but I will resubmit it now that I am in the guard and the lines of communication are a little more open.
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crackhead

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Unread post06 Aug 2009, 21:56

You may be able to lower the landing gear by using the alternate landing gear system. by pulling the t handle, nitrogen is released into the system and push the doors open and gear down.
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crackhead

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Unread post06 Aug 2009, 22:12

Oops, maybe I should finish reading. FNG's!
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meyer

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Unread post29 Oct 2009, 15:15

There is an emergency gear accumulator which does an "alternate extension" of the gear. It uses nitrogen to blow the gear down in an emergency. The funny thing, from a maintenance perspective is that there is no main gear door sequencing when it does that so it smacks the sh*t out of the doors when the main gear comes out of the hole. the nose gear doesnt lock very well unles there is airspeed pushing against it to help it lock in place. The gear does not need any hydraulic power to be extended in an emergency situation.
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BouliNDSO

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Unread post29 Oct 2009, 15:27

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?


Yes you can still lower the LDG with Alternate gear selection. This will push all the gear doors open with nitrogen and the MLG will drop down by gravity, the NLG will also be pushed out with nitrogen. That is also the reason NWS will not work anymore because of the Nitrogen being pushed in the LG down hydraulic tubes..

Brakes can still be used for 75 sec's with moderate steady application (75 sec's is pretty long even for a normal landing). And some countries will still be able to use the Drag chute which is also connected on the B system but is still usable via an accumulator.
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BouliNDSO

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Unread post29 Oct 2009, 15:34

meyer wrote:There is an emergency gear accumulator which does an "alternate extension" of the gear. It uses nitrogen to blow the gear down in an emergency. The funny thing, from a maintenance perspective is that there is no main gear door sequencing when it does that so it smacks the sh*t out of the doors when the main gear comes out of the hole. the nose gear doesnt lock very well unles there is airspeed pushing against it to help it lock in place. The gear does not need any hydraulic power to be extended in an emergency situation.


It's correct that the gear will come down unsequenced, but the Nose gear does ONLY extend with nitrogen pressure because it has to extend AGAINST the airflow. Just look at some pictures and you will notice that the Nose gear extends against the flow.
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ljqc

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Unread post27 Aug 2010, 13:19

It's correct that the gear will come down unsequenced, but the Nose gear does ONLY extend with nitrogen pressure because it has to extend AGAINST the airflow. Just look at some pictures and you will notice that the Nose gear extends against the flow.


Yeah, and the NLG will get stuck if extended above 190 KTS~
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jokes81

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Unread post28 Aug 2010, 03:51

aim-120c5 wrote:Does anyone else know something about the first two questions? A real pilot maybe? If someone knows please answer. :D



Did this clown just ask a for a "real pilot" to answer his question about how a jet works (outside of the cockpit)? First off if you don't like the answer a crew chief gives go play back to your room and play Aces of Combat and figure it out for your self.
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VarkVet

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Unread post28 Aug 2010, 08:57

jokes81 wrote:
aim-120c5 wrote:Does anyone else know something about the first two questions? A real pilot maybe? If someone knows please answer. :D



Did this clown just ask a for a "real pilot" to answer his question about how a jet works (outside of the cockpit)? First off if you don't like the answer a crew chief gives go play back to your room and play Aces of Combat and figure it out for your self.


:shock: Now that is funny! :lmao:
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mlk32170

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Unread post16 Dec 2010, 20:39

aim-120c5 wrote:1. I know the F-16 has two hydraulic systems according to F4AF, A and B, right? The A controls the speed brakes and fuel flow proportioner and B landing gear, NWS, gun, wheel brakes, JFS recharge, drag chute system, and air refueling. Is this correct?

2. Now, in case the engine fails in the air the EPU will provide emergency hydraulic power only to A system. The wheel brakes and the NWS still work in F4AF after a flameout landing, altough in the manual says the B system is not working if the engine is not working. Do the wheel brakes and NWS work in a real F-16?

3. And why does the EPU power the fuel proportioner if the engine is dead? Why do I need fuel flow then?


The FFP is on system A because the sys A is more reliable. System B contains all the 'non-essential' components. Adding these components to the systems reduces the reliability of the system. System A is set up to minimize failure rates that will impact flight critical components.
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exfltsafety

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Unread post17 Dec 2010, 02:03

The FFP is on system A because the sys A is more reliable. System B contains all the 'non-essential' components. Adding these components to the systems reduces the reliability of the system. System A is set up to minimize failure rates that will impact flight critical components.

I don't agree with the implication that the FFP and speedbrakes (also on system A) are flight critical. The engine runs fine without the FFP and the aircraft can be flown and landed safely without the speedbrakes. Flight critical components like the flight controls receive hydraulic power from both systems.
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anchor

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Unread post05 Feb 2011, 10:06

Pilot's guide to the B system
GANGBANG
Gear
A/R Door
NWS
Gun
Brakes
Accumulators (JFS)

Close enough
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abufarah001

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Unread post22 Apr 2011, 20:01

THE F-16 EPU PROVIDE HYD ONLY FOR SYS A AND THATS COUSE THE EPU HYD PUMP IS SMALLER THAN THE ENG DRIVEN HYD PUMP AND SYS A IS SMALLER THAN SYS
B.
SO WHEN LOOSING THE ENG POWER THEN BOTH HYD SYSTEM A & B ARE LOST TOO
SO THE EPU WILL COME ON LINE PROVIDING HYD PRESS. TO SYS A & ALSO PROVIDING ELECT POWER TO CONTROL THE JET
SO THE LG WILL LOWERD ONLY USING THE N2 (ALTERNAT)
NO NWS IS AVAILABLE AND THE BRAKES WILL WORK USING THE PRESS IN THE JFS/BRAKES ACCUMULATORS
WE NEED THE FFP TO KEEP THE CENTER OF GRAVITY OF THE JET
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abufarah001

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Unread post22 Apr 2011, 20:18

LOWERING THE LG USING N2 WILL BE :
1- THE MLG DOORS WILL OPEN USING N2 PRESS. AND WHEN THE DOORS ARE FULLY OPEN THE UPLOCK HOOKS ARE OPEN
SO THE MLG WILL FALL DOWN BY THE WIGHT (SAME AS SYS B IS WORKING NORMALLY) AND IN THE MLG THE SEQUANCE IS MECHANICAL FIRST THE DOORS OPENED THEN THE MLG FALL DOWN.
2- THE NLG OPENED AGAINST AIR MOVEMENT SO THEY NEED PRESS SO BOTH OF NLG DOOR ACTUATOR AND NLG EXT/RET ACTUATOR HAD A 3 HOSES (2 FOR HYD PREES & 1 FOR N2 PRESS) SO THE DOOR AND THE LG WILL OPEN TOGSTHER WITH NO SEQUANCE USING N2 PRESS.
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exfltsafety

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Unread post22 Apr 2011, 20:56

abufarah001 wrote:WE NEED THE FFP TO KEEP THE CENTER OF GRAVITY OF THE JET

The center of gravity position will not likely become a problem in the time from when the emergency occurs until landing. If the pumping elements of the FFP are not rotating, fuel flows from each reservoir through bypass passages of equal size. In addition, there is no cockpit indication of failure of the FFP - so it can't be a flight critical component.
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