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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aim-120c5

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Unread post23 Aug 2008, 19:15

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?
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That_Engine_Guy

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Unread post23 Aug 2008, 22:00

aim-120c5 wrote:3. And why does the EPU power the fuel proportioner if the engine is dead? Why do I need fuel flow then?


Because the EPU may activate even if the engine is running fine...

Lets not forget the EPU isn't just a backup for an "engine failure":doh:

Say if your PTO shaft fails; or the ADG fails, or a HYD A system failure, or primary power failure, etc. :shrug:

There are far more EPU activations for electrical and hydraulic problems than engine failures.

So if the EPU activates to provide backup power and/or hydraulics in these types of situations, you may still need to monitor your engine instruments because that motor is running and still pushing you home!... :salute:

Keep 'em flyin' :thumb:
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aim-120c5

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Unread post08 Sep 2008, 20:16

Does anyone else know something about the first two questions? A real pilot maybe? If someone knows please answer. :D
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mostroscuro

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Unread post08 Sep 2008, 22:05

I'm no pilot, and it's been a while since I crewed a 16, but here goes:

The brakes will still be operational on a B sys failure because of the JFS/brake accumulators. They'll provide hydraulic power to the brakes for a limited time/number of uses. Basically enough to get to a stop and get towed back to the parking spot.

To the best of my knowledge, and I don't have a -29 to back me up, but once B sys is gone, NWS is gone. The centering cam will center the wheel before it touches, but that's it - no steering.

Either situation would probably warrant dropping the tailhook. The main goal here is not to try and taxi the jet all the way back to its parking spot - it's to get the pilot and the jet safely to a stop on the ground.
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88ee

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Unread post09 Sep 2008, 02:27

Yes, the brakes work under EPU Hyd power, the Accumulators are a last ditch effort to provide braking power. As for NWS ... not so much.
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VarkVet

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Unread post09 Sep 2008, 03:49

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


If you don't like the answers you got ... go ask Jeeves :twisted:
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Tim

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Unread post09 Sep 2008, 15:18

If you don't like the answers you got ... go ask Jeeves

I had no Idea that Jeeves was a former Crew Dawg :thanks:
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Kaasjager.

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Unread post09 Sep 2008, 16:26

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?


Take a look here and all will be explained.
http://img300.imageshack.us/my.php?imag ... 490yp1.jpg
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CIMG0490.jpg
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JpoLgr

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Unread post09 Sep 2008, 22:04

88ee wrote:Yes, the brakes work under EPU Hyd power, the Accumulators are a last ditch effort to provide braking power. As for NWS ... not so much.


Sorry mate, no braking under EPU Hyd power!

The brakes work in such a case only by the Brake/JFS acumulators, for a single (75sec max) application, just for stopping (as you and the other guys said).

aim-120c5:

1. CORRECT
2. NO
3. What that engine guy wrote :D .

Cheers, John.
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88ee

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Unread post10 Sep 2008, 02:42

Well there you have it ... that's what I get for relying on 8 year old memory ... nice diagram btw.

I still have my original FTD Environmental "you color it" diagram from 1991 ... funny some of the crap we keep over the years.
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JpoLgr

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Unread post11 Sep 2008, 19:03

Hey 88ee, memories are the only thing we carry with us!!

P.S. keep relying on your mem, this was a minor mistake!

Cheers, John.
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aim-120c5

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Unread post13 Sep 2008, 12:47

Ok, thanks you all. You hepled a lot. If someone has something to add on this thread, feel free to add to it. :D
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NANCYFALCON

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Unread post15 Mar 2009, 14:29

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 following info will cover you questions i think.
1. System A AND system B provide hydraulic pressure to:
>The Primary Flight Controls: Flaperons, Horizontal Stabilizers and
Rudder
>Secondary Flight Control: Leading Edge Flaps
(Flight controls are the most important, so they work on both systems)

System A:
>Speedbrakes (also referred to as a secondary flight control in the TO)
>Fuel Flow Propotioner

System B:
>Landing Gear System
>Wheel Brakes
>Nose Wheel Steering
>Dragchute
>Aerial Refueling System
>Engine Starting System
>Gun System

2. #Brakes will still work if there still is hydraulic pressure in the JFS/Brake
accumulators.
#NWS can only work with Landing Gear Down pressure. Because that is
connected to system B, no pressure > no NWS. If taxiing is needed it
can be done by applying brake pressure on only the left or the right
main wheel.

3. The goal of the Fuel Flow Propotioner is to maintain center of gravity of
the airplane by providing an equal usage of fuel from the reservoir tanks.
Maintaining the center of gravity is also very important for this aircraft to
keep it in flight.

As you see you don't have pressure to the systems that are connected to system B in an emergency. Or they are not important enough for the aircraft to maintain to fly and land or they have a built-in back up.
>LDG; down selection is still possible with the help of nitrogen
>Wheelbrakes; as already mentioned, the hydr press in the accumulators,
and if that is not enough stopping power and the aircraft does not have a
dragchute, the arresting hook can be used. It works with nitrogen (from
the same bottle as for the LDG)
>NWS; see answer question 2
>Dragchute; it can still be used with hydr pressure from it's accumulator
>Aerial Refueling and Gun system are not systems you need if you want land as soon as possible, so no back up
>ESS; if required a start of the JFS can be attempted with the help of hydr press from the JFS/Brake accumulators

Hope this covers your questions :)
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VarkVet

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Unread post15 Mar 2009, 14:39

F-16 hydraulics according to Varkvet.

If you look at the 6 WC there is nothing that tells you to dump your reservoir accumulators upon engine shutdown or while performing any inspection. Dumping is just a standard crew dawg procedure to relieve system pressure for two reasons. 1. You relieve system pressure so your jet doesn’t sit there and start leaking all over the ramp like F-4’s and Wonder lemons. 2. Dumping the system is a good way of seeing how much air is in your jet … Check fluid level at 3000 psi and then again at pre-charge, when you dump it, B system fluid level should not increase more that 3% and A no more than 5%.
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slay0r

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Unread post24 May 2009, 18:42

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