JFS Operation
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I’m reading in the actual T.O. GR1F16CJ1, p.1-36/7, that the JFS will continue to run, airborne after it’s started, until the JFS switch is manually positioned to OFF. The JFS runs on aircraft fuel and will run even after the fuel master switch is subsequently turned OFF. This is not what I’m seeing in the sim. I started the JFS below FL200 and 400kts, and allowed it to run for over 15 minutes, as I recall, and it was running as advertised. However, when I shut down the engine with the master fuel switch to OFF, it stopped running after about 4 more min, as I recall. Once started, as it was, it should not have stopped running until all fuel on the aircraft was consumed. During a flameout landing the dash 1 says I need to see 25% hydrazine fuel remaining on the EPU gauge at the hi key position, or 20% if the JFS is running. Obviously, I would like to have the JFS running during the flameout approach to give me this added safety margin. Is this not modeled correctly, or am I missing something in understanding the operation of the JFS? Thanks, Trippp
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https://www.quora.com/How-do-you-start-the-engine-on-an-F-16-Fighting-Falcon
http://www.f-16.net/forum/viewtopic.php?t=2002 sources that say differently, both crew chiefs
basicly the JFS is nothing but 2 bottles of 3000psi compressed gas that spin up the engine to 20 percent, after 20 percent the throttle is moved into idle (and maybe even advanced a little at that point, not sure if that happens at 20 or 40 percent rpm) and at 40 percent the JFS should automaticly switch off (it’s a magneto switch)
edit: reading your post again but replacing JFS with EPU makes your post make a heck of a lot more sense, you sure that you are not confusing Jet Fuel Starter with Emergency Power Unit?
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https://www.quora.com/How-do-you-start-the-engine-on-an-F-16-Fighting-Falcon
http://www.f-16.net/forum/viewtopic.php?t=2002 sources that say differently, both crew chiefs
basicly the JFS is nothing but 2 bottles of 3000psi compressed gas that spin up the engine to 20 percent, after 20 percent the throttle is moved into idle (and maybe even advanced a little at that point, not sure if that happens at 20 or 40 percent rpm) and at 40 percent the JFS should automaticly switch off (it’s a magneto switch)
edit: reading your post again but replacing JFS with EPU makes your post make a heck of a lot more sense, you sure that you are not confusing Jet Fuel Starter with Emergency Power Unit?
No, he isnt confusing them. The JFS is a bit more than the accumulators.
Regarding your explanation of what the JFS is, Id recommend a return to the manuals for a bit. Dash has this to say:
The JFS is a gas turbine which operates on aircraft fuel and drives the engine through the ADG. The JFS is connected by a clutch to the ADG and only provides torque when required to maintain engine rpm. If the ADG is not able to rotate (i.e., seized engine), the JFS runs, but the clutch prevents it from rotating the ADG. The JFS receives fuel at all times regardless of the FUEL MASTER switch position. The JFS is started by power from two brake/JFS accumulators used either singly or together. The brake/JFS accumulators are charged automatically by hydraulic system B or manually by a hydraulic hand pump located in the left wheel well. Automatic recharging takes between 40 seconds (hot ambient conditions) and 60 seconds (cold ambient conditions). The JFS is used to start the engine on the ground and to assist in engine airstart. Refer to JET FUEL STARTER LIMITS, Section V.
For the purposes of the other thread, ADG is Accessory Drive Gearbox, JFS is the Jet Fuel Starter.
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No, he isnt confusing them. The JFS is a bit more than the accumulators.
ok, yea i read that once i read my 2nd link a bit further down. but in the end what drives the JFS is still just those 1 or 2 bottles (depending on how you set the switch).
why that would affect hydrazine i don’t know unless that extra 5 percent is gained from the marginal amount of thrust that the JFS generates while gliding.i’ll grab a seat and watch this topic, might learn something really interesting here.
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JFS is not fully implemented as in reality in the sim
We use it just to start the engine, past that in flight ops is not fully accurateSo taking information in the real docs won’t help you but rather confuse you
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but in the end what drives the JFS is still just those 1 or 2 bottles (depending on how you set the switch).
why that would affect hydrazine i don’t know unless that extra 5 percent is gained from the marginal amount of thrust that the JFS generates while gliding.The bottles don’t drive the JFS, they start it. But once it’s running it’s just a sort of little jet engine. It doesn’t generate useful thrust though but just powers a bunch of useful stuff and gets the engine going.
The JFS (when running) reduces the load on the EPU, conserves EPU fuel and partially restores hydraulic system B. That’s why it allows you to fly a flameout landing with reduced EPU fuel.
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The JFS works differently for starts on the ground and in the air. The JFS/Brake accumulators are for starting the JFS operation. Once started IN THE AIR it should continue to run. For a ground start it automatically shuts off at a certain time/rpm whatever. I was questioning the air operation. T
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Mostly correct answers here. It shuts off at 50% RPM on the ground, in there air it does not. However, in flight with a working engine, the max time limit for the JFS is 3 minutes. There are certain EPs you do not want to start the JFS (fire, fuel starvation, or imminent engine seizure).
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I’m grasping at understanding at this but I think the JFS is an intermediary between the stored pneumatic bottle(s) and the full engine. There is some mention of using the JFS as a way to supplement the EPU in the case of engine failure. The JFS actually burns JP-8 in a piggyback arrangement on the engine. The pneumatic accumulator bottles blow the JFS to turn and the JFS turning makes the engine turn. The JFS is making the engine turn by a torque on an engine gearbox output-input shaft and is declutched from the engine operation when the torque inverts.
The JFS is sort of a pneumatically-started APU geared and clutched into the main engine. The pneu bottle air doesn’t blow directly on the compressor/turbine stages of the main engine. It’s shafts and gearboxen.
Pneumatic bottle -> hydraulic fluid -> JFS -> ADG -> (internal clutch) -> PTO shaft -> engine.
What I’m not sure of if the JFS actually consumes JP-8 or not when self-sustaining. From the sound of it by the JFS exhaust duct and doors it must burn fuel to turn the main turbine over.
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“The JFS is a gas turbine that operates on aircraft fuel”
Im gonna go ahead and say yeah it does.
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The JFS is sort of a pneumatically-started APU geared and clutched into the main engine. The pneu bottle air doesn’t blow directly on the compressor/turbine stages of the main engine. It’s shafts and gearboxen.
What I’m not sure of if the JFS actually consumes JP-8 or not when self-sustaining. From the sound of it by the JFS exhaust duct and doors it must burn fuel to turn the main turbine over.
Ok a few things. I am not an engine/JFS guy but the accumulators should work the same as others. That would mean the air pressure is only to push against the hydraulics in the accumulators and the hydraulics are what does the actual spinning of the JFS. No air at the JFS to start it.
Yes the JFS uses the same fuel as the main engine and will consume some to stay running. Both of the flight manuals I referenced agree that the master fuel shutoff has no bearing on JFS operation.
Pneumatic bottle -> hydraulic fluid -> JFS -> ADG -> (internal clutch) -> PTO shaft -> engine.
JFS/Brake hydraulic accumulators > hyd lines to JFS > JFS start then the rest.
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Maybe we should request a Viper Haynes manual…
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Maybe we should request a Viper Haynes manual…
The Chilton’s are usually helpful too, just less pictures :rofl:
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Maybe we should request a Viper Haynes manual…
You mean like this?
It’s been done. It’s a good series, not actually a Technical Manual, but rather a general interest book. There’s a fair bit of technical stuff though, along with a good training sortie description by a Viper driver.
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You mean like this?
It’s been done. It’s a good series, not actually a Technical Manual, but rather a general interest book. There’s a fair bit of technical stuff though, along with a good training sortie description by a Viper driver.
… and if Haynes had any input, it’ll be full of inaccuracies!
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… and if Haynes had any input, it’ll be full of inaccuracies!
Yeah I’ve heard that more and more over the years. They don’t even do one for the petrol mark 2 Octavia, and look how popular that car is!
Still, could be tempted to get that F-16 haynes for the novelty feature.
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Still, could be tempted to get that F-16 haynes for the novelty feature.
You know you want to click that button… http://www.ebay.co.uk/itm/361841938227
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You know you want to click that button… http://www.ebay.co.uk/itm/361841938227
Damn, the last one just sold.
Oh wait, to me! Good times!
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Damn, the last one just sold.
Oh wait, to me! Good times!
Enjoy it. It’s a good read. Can I recommend the titles on the SR-71, B-52, Harrier and Phantom in the same series. They’re the good ones of a somewhat variable bunch.
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Enjoy it. It’s a good read. Can I recommend the titles on the SR-71, B-52, Harrier and Phantom in the same series. They’re the good ones of a somewhat variable bunch.
I only have eyes for the Viper, but thanks. Looking forward to geeking out by reading it