Jet fuel starter (JFS) turning off too soon
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Looking in the -1 it looks like the JFS has a regulatory limit of 4 minutes run time motoring the engine until it is required to turn it off for cooling. In BMS the JFS stops motoring and the run light blinks in much less than this much time.
The accumulator(s) start the JFS but once the JFS is burning fuel it should continue indefinitely. Yes/no?
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Hold on… Not sure I get what you’re trying to ask here…
My understanding of the JFS system is that it is relying on 2 pressurized bottles.
JFS 1 will only use one, JFS 2 will use both.Real F-16 pilots say they almost never use JFS 1 as there is a high probability it will fail as it requires a very favorable situation.
Once the engine has spooled high enough (40% AFAIK), the JFS will stop and the engine will continue the spool up to 70% for idle rpm.If you’re operating the canopy also during JFS, it will draw too much power resulting in JFS failure as well…
Hope that answer part of your questions…
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Looking in the -1 it looks like the JFS has a regulatory limit of 4 minutes run time motoring the engine until it is required to turn it off for cooling. In BMS the JFS stops motoring and the run light blinks in much less than this much time.
The accumulator(s) start the JFS but once the JFS is burning fuel it should continue indefinitely. Yes/no?
JFS modeling is accurate
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If you’re operating the canopy also during JFS, it will draw too much power resulting in JFS failure as well…
IIRC, this is only during JFS start sequence. To be confirmed.
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Frederf,
Follow these four steps and do nothing else with any other settings in your jet :-
1. make sure throttle is “off”, not just at idle, check your detent position in your controller set up.
2. ELEC panel set switch to “Main PWR”
3. FUEL panel set knob to “NORM”
4. ENG panel switch to “STRART 2”These steps should get you engine up to 25% then take you throttle passed the detent, that is to say throttle to idle (these are two different things) then let the RPM rise to 70% WATCH YOU FTIT while your RPM is going from 25% to 70% if the FTIT gets a head of your RPM there is a good chance you have given too much throttle and you now have an engine fire - if so simply return throttle to the other side of detent and let the RPM settle back to 25% and the FTIT come down until it settles at which point you can push the throttle to idle - rinse and repeat.
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I’m lost, is he saying he has a problem or is he asking a question about how realistic the JFS model is?
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I read it as he was having a BMS problem ??? if not please ignore my post …
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I’m reading that he has found that the JFS runs for less time then the published 4 minutes of run time (requiring it to be shut off so as not to over heat the JFS). I don’t guess I’ve ever let it run more than a couple of minutes until it shuts itself off during ramp. In my mind… it would seem you’re having a bad day if 4 minutes have passed, and you haven’t lit the candle…
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I could be wrong, but my read is that the JFS is run entirely off of the accumulators.
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The JFS starts off the accumulators. The JFS runs on jet fuel. Once the JFS run light is on and the JFS is burning JP-8 you can remove the accumulators and throw them over a fence.
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The JFS starts off the accumulators. The JFS runs on jet fuel. Once the JFS run light is on and the JFS is burning JP-8 you can remove the accumulators and throw them over a fence.
You got to call a fence in first, I’m not sure this is very realistic.
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Typically the accumulators are used in order to spin a hydraulic motor which is connected to the JFS. When the JFS starts running then fuel is used in order for the starter to accomplish 100% rotation and start rotating the main engine via a gearbox.
When you have a fully running JFS there is a steady green light. When the JFS is not starting properly then the light flashes.
The detail here is that the use of the accumulators is not only for spooling up the engine. The accurate name of the accumulators is “JFS/brake accumulators”.
So the accumulators can be used in order to brake the aircraft while you are on battery and the main gen is offline.You can easily understand that if you hit the brakes or the parking braking before the jfs run light is on and steady then you have the hung start case because the accumulators are depleted in order to brake the aircraft and the pressure is not enough in order to rotate the hydraulic motor and the JFS in 90%(JFS rpm, NOT engine rpm) which is the state that gives you the green steady run light.
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I could be wrong, but my read is that the JFS is run entirely off of the accumulators.
I think you are mistaken. The JFS is started from the accumulators stored pressure, fuel is introduced and then it runs off fuel. There’s, if I recall correctly, a note about how the JFS always receives fuel and you can’t actually cut off its fuel supply with cockpit switches.
Frederf, for your initial question: I was under the impression the JFS is supposed to automatically switch itself off during engine start, once the engine is running (greater than 50% RPM?). The limit on runtime I’d thought was if you are motoring the engine without it operating.
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Exactly. I start JFS, run light comes on, then just wait. I do not attempt an engine start. My expectation is that JFS will continue to run until fuel is exhausted or something breaks.
From reading section V JFS should break not sooner than 4 minutes motoring and probably in reality running until destruction/fault much longer.
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Exactly. I start JFS, run light comes on, then just wait. I do not attempt an engine start. My expectation is that JFS will continue to run until fuel is exhausted or something breaks.
From reading section V JFS should break not sooner than 4 minutes motoring and probably in reality running until destruction/fault much longer.
A JFS RUN light flashing once per second indicates a noncritical failure in the JFS system.
If the JFS operates normally for engine start, the mission may be continued.A JFS RUN light flashing twice per second indicates a critical failure in the JFS system.
The JFS will not operate. Place the MAIN PWR switch to OFF.BMS simulates both conditions.
While still on the ground , the JFS will flash once per second after 4 minutes of continuous operation from the time JFS has reached governed speed ( green light).The JFS is stating to overheat.
If you leave it on anther 4 minutes, the JFS light will flash 2 times / second indicating a critical failure. -
Thanks. I just did a stopwatch run and run light started blinking 3:57 after it came on. But then I did a second run and it didn’t last to the two minute mark. I also tried various combinations of engine feed and air source. Sometimes the JFS runs for 4+ minutes, sometimes it doesn’t.
With engine feed off, air source off, main power, start 2 this is the following stopwatch time from run light on to blinking at various time accelerations:
1x 4:00 (4m sim)
2x 1:55 (4m sim)
4X :29 (2m sim)
8x :07.5 (1m sim)
16X :02.4 (1/2m sim)I know moving the canopy will insta-off the JFS. Apart from canopy I don’t know anything else that will. I’m not messing with time accel too often but that’s certainly one thing that’s artificially shortening the JFS run time. There might be others.
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Thanks. I just did a stopwatch run and run light started blinking 3:57 after it came on. But then I did a second run and it didn’t last to the two minute mark. I also tried various combinations of engine feed and air source. Sometimes the JFS runs for 4+ minutes, sometimes it doesn’t.
With engine feed off, air source off, main power, start 2 this is the following stopwatch time from run light on to blinking at various time accelerations:
1x 4:00 (4m sim)
2x 1:55 (4m sim)
4X :29 (2m sim)
8x :07.5 (1m sim)
16X :02.4 (1/2m sim)I know moving the canopy will insta-off the JFS. Apart from canopy I don’t know anything else that will. I’m not messing with time accel too often but that’s certainly one thing that’s artificially shortening the JFS run time. There might be others.
By second run do you mean that you switch off the JFS, an on again?
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No, running the entire mission again.
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Thanks. I just did a stopwatch run and run light started blinking 3:57 after it came on. But then I did a second run and it didn’t last to the two minute mark. I also tried various combinations of engine feed and air source. Sometimes the JFS runs for 4+ minutes, sometimes it doesn’t.
With engine feed off, air source off, main power, start 2 this is the following stopwatch time from run light on to blinking at various time accelerations:
1x 4:00 (4m sim)
2x 1:55 (4m sim)
4X :29 (2m sim)
8x :07.5 (1m sim)
16X :02.4 (1/2m sim)I know moving the canopy will insta-off the JFS. Apart from canopy I don’t know anything else that will. I’m not messing with time accel too often but that’s certainly one thing that’s artificially shortening the JFS run time. There might be others.
You can’t do measurements in time acceleration it can not work properly for timers here
Only x1 is accurate
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There might be others.
Have you observed others? Im a little surprised to see testing other speeds other than 1x - Id been under the distinct impression the time compression modes were still under “here be dragons” territory.