4.34 U1 - Hyd B failure causes total loss of MLG brakes
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Isn’t that the principle of operation of the accumulator, they accumulate fluid, isolated from the leaking circuit and allow to use it for specific functions once in an emergency
that’s why brake, flcs and parachute have their own accumulators. Check the service diagrams in the real dash-1F-16 Brakes can be employed once after a SYS B failure, exactly thanks to the accumulator
Brake hydraulic power is supplied by system B. If system B fails or the engine is operating at less than 12 percent rpm, the toe brakes and parking brake are available until the brake/JFS accumulators deplete. Continuous use of the toe brakes, even with the parking brake set, depletes accumulator fluid and causes loss of all braking capability after approxi mately 75 seconds (brake/JFS accumulators initially fully charged). When holding the aircraft stationary, use of the parking brake is preferred since brake/JFS accumulator fluid is not depleted.
After touchdown from a flameout landing, use a normal or short field stopping technique as required by the stopping distance available. If the JFS and EPU are running, normal braking and NWS are available (NWS is inoperative if the LG was lowered with the alternate LG system). If the JFS is not running, only the brake/JFS accumulators are available to supply hydraulic pressure for braking. Stop the aircraft by making one steady brake application just short of antiskid cycling. If there is any doubt about stopping on the remaining runway, lower the hook. When the aircraft is fully stopped,
and finally:
SYSTEM B FAILURE
NOTE
EPU RUN light on may indicate a dual hydraulic or PTO shaft failure.
The FLCS ISA’s are operating in the nonredundant mode and normal braking, NWS, AR door operation, gun operation, and normal LG extension are lost. Low hydraulic pressure may cause one or more LG actuators to remain locked in the LG up position. LG extension should be attempted in sufficient time to prepare for possible LG up landing. Drag chute operation is normal using drag chute accumulator pressure. Braking is available using brake/JFS accumulator pressure. The fully charged brake/JFS accumulators contain sufficient fluid for at least 75 seconds of continuous brake application. Use aerodynamic braking to the maximum extent possible. A single moderate and steady brake application without cycling the antiskid should then be applied. After stopping, engage the parking brake. If there is reason to believe that the brake/JFS accumulators are depleted or that directional control may be a problem, an approach end arrestment should be considered.To the OP: As said below: parking brake could also be used in an emergency after the brake accumulator have been depleted
PARKING BRAKE C DF
The parking brake is activated by the ANTISKID switch located on the LG control panel, and supplies full, unmetered pressure to three of the six pistons in each brake. The parking brake holds the aircraft stationary without the use of toe brakes. It can also be used for emergency braking if the toe brakes are inoperative. The parking brake is powered by battery bus No. 2 and system B hydraulics or one brake/JFS accumulator (the brake/JFS accumulator which is not used for START 1). -
I lost SYS B two times in U1 ans was not able to use wheel brakes after landing. So in theory this is all fine but it doesn’t seem to work in U1. Or I did something terribly wrong (except of being hit and lost SYS B )
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@Red:
To the OP: As said below: parking brake could also be used in an emergency after the brake accumulator have been depleted
I tried that too but it didn’t work either.
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I think I found the explanation to my problem:
-1 pg.141
1.13.2. Wheel brakes
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Brake hydraulic power is supplied by system B. There is no emergency brake implemented in BMS. In the real jet the JFS accumulator is able to power the brakes in case of a dead stick landing. To overcome the issue BMS toebrakes remain active even when the aircraft is running on EPU.What does this exactly mean though?
Do toebrakes remain pressed and keep draining JFS accumulator power when running on EPU (would explain my issue)
or do the toebrakes remain operational regardless of Hyd B pressure (would conflict with my observations of the issue)? -
Bear in mind that the docs haven’t been updated for 4.34.1 as it’s mostly bugfixes.
What you stated from the docs are relevant for 4.34 (and were specifically tested) and may not be anymore for 4.34.1 as this specific area was obvioulsy changed as per the changelog
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@Red:
What you stated from the docs are relevant for 4.34 (and were specifically tested) and may not be anymore for 4.34.1 as this specific area was obvioulsy changed as per the changelog
The changelog doesn’t look like it would affect my issue, I guess I’ll just test this in U0 since I can’t recall encountering it previously.
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@Red:
Bear in mind that the docs haven’t been updated for 4.34.1 as it’s mostly bugfixes.
What you stated from the docs are relevant for 4.34 (and were specifically tested) and may not be anymore for 4.34.1 as this specific area was obvioulsy changed as per the changelog
To accompany Rusher’s post:
I just tried the flame-out landing in a simple TE in 4.34U1. I started from “runway” with an C-50 in standard KTO. I climbed to 30000 ft and shut the engine down, starting the EPU-powered glide. Monitoring the EPU fuel and the HYD B pressure gauges, I noticed that the HYD B slowly depleted on its own despite not touching the rudder pedals nor the toe brakes during the glide. Parking brake was off throughout the flight. Eventually, HYD B pressure depleted to 0 before I landed. As a result, I couldn’t stop the jet on the landing roll. On another test with the same setup, HYD B pressure decayed at a similar rate despite not giving any flight control inputs.
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To accompany Rusher’s post:
I just tried the flame-out landing in a simple TE in 4.34U1. I started from “runway” with an C-50 in standard KTO. I climbed to 30000 ft and shut the engine down, starting the EPU-powered glide. Monitoring the EPU fuel and the HYD B pressure gauges, I noticed that the HYD B slowly depleted on its own despite not touching the rudder pedals nor the toe brakes during the glide. Parking brake was off throughout the flight. Eventually, HYD B pressure depleted to 0 before I landed. As a result, I couldn’t stop the jet on the landing roll. On another test with the same setup, HYD B pressure decayed at a similar rate despite not giving any flight control inputs.
I will test this night this issue. I just confirmed that this behaviour is not supposed to happen.
Brake operations during an engine fail or engine shutdown must be normal and operational (if no other Hyd problems are present).
IRL emer procedures advise on using arrestor cables if present in the emerg AB due to depletion of Hyd fluid.
We really need the arrestor cable to start working on BMS. If they work on carriers then it cannot be that difficult to place them in air bases.
This video shows this very well.
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Ok, I just tested it in U0, brake operation is completely normal. As opposed to U1 where now it’s impossible to brake without Hyd B pressure.
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Great video!
A bit off topic: i notice the Gear bracket is not shown in the HUD?
Happy newyear!
Snowman
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Why do you say that JFS should power the brake accumulators ?
If you have a leak of hydraulic fluid , that means you don’t have fluid anymore so you can’t have pressure in the system
Not the JFS, the JFS accumulators and the JFS accumulators are the brake accumulators. The accumulators are really close to the brakes (check valve back to the system) so you can lose fluid in a lot of the rest of the system but as long as the pipe connecting the bottle to the brake is intact you still have brakes. Both bottles are attached to both brakes so even if one accumulator circuit is down there is reduced force available. The B system gauge is outside the brake circuits so zero pressure displayed or even total loss of fluid in that portion of HYD B doesn’t negate emergency braking. It’s possible to lose fluid and/or pressure in the braking sections but that’s more specific than just loss of fluid or pressure in HYD B.
No, the parking brake cannot be used if there is no pressure. It can be used if the toe pedals (and just the pedals) don’t work but it needs pressure from somewhere. Parking brake is powered by the same accumulator energy but bypasses the metering valves associated with the pedals.
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Why do you say that JFS should power the brake accumulators ?
If you have a leak of hydraulic fluid , that means you don’t have fluid anymore so you can’t have pressure in the system
You have had too much wine buddy. You have already fixed the HYD system as per the -1
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@Red:
Isn’t that the principle of operation of the accumulator, they accumulate fluid, isolated from the leaking circuit and allow to use it for specific functions once in an emergency
that’s why brake, flcs and parachute have their own accumulators. Check the service diagrams in the real dash-1F-16 Brakes can be employed once after a SYS B failure, exactly thanks to the accumulator
and finally:
To the OP: As said below: parking brake could also be used in an emergency after the brake accumulator have been depleted
If you want to release the 4.35 now, you are welcome , but better hurry to update the manuals
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You have had too much wine buddy. You have already fixed the HYD system as per the -1
I know what I did mate
But I also know what is in 4.34 and what is not
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So in short
We know how all Of this works
It’s been already coded properly but not’for 4.34
In 4.34 no hydraulic system means you have an hydraulic leakage at a position where the accumulator can not work
You will have to Live with it for 3 to 4 weeks
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I know what I did mate
But I also know what is in 4.34 and what is not
Sure you do and kudos for the extras.
I think it would have been better to say " Hey… 4.34, has no JFS/brake accumulators coded, so any loss of hydraulic fluid in the B system will certainly make braking inoperative." -
Sure you do and kudos for the extras.
I think it would have been better to say " Hey… 4.34, has no JFS/brake accumulators coded, so any loss of hydraulic fluid in the B system will certainly make braking inoperative."Îm’ sure if we have a leak after the accumulator we won’t have brakes
Should I code this as well now ? LOL
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A bit off topic: i notice the Gear bracket is not shown in the HUD?
Good catch! I’ve never paid attention to this!
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So in short
We know how all Of this works
It’s been already coded properly but not’for 4.34
In 4.34 no hydraulic system means you have an hydraulic leakage at a position where the accumulator can not work
You will have to Live with it for 3 to 4 weeks
So we have no way of safely landing a jet after taking battle damage now. Why is this new though? It wasn’t like this in U0.
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Îm’ sure if we have a leak after the accumulator we won’t have brakes
Should I code this as well now ? LOL
Eventually. Depends on the surface area of the leak. How much flow rate there is of fluid, how much pressure there is supplied by system pumps and the accumulators, how much fluid there is to spare…
It’s not an instant case of a total loss of all pressure the second there’s a leak.