Jet fuel starter (JFS) turning off too soon
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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.
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Most of Time related things does not work with time compression , JFS in particular
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The JFS Does have a fuel s/o valve located in the rt flaperon ISA compartment that gets a signal from the JFS controller. The JFS does have a time limit on ground to avoid overheat. it does not have a limit in air, it can run continuously till fuel runs out or meltdown, which ever comes first. When system was using the old analog controllers(80’searly90’s), failures were quite frequent. The controller would fail as soon as a parameter was exceeded even for a millisecond. The new digital controllers were a godsend, they allowed a momentary exceedance of parameters as long as it stabilized within parameters after exceedance and start would continue. We would have the Hyd mule standing by for pressurizing B sys accumulators instead of hand pumping.
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I am using 4x quite a lot, is that something I shouldn’t do? It is sooo useful, especially during startup (imagine actually spending 20 min on the ground) and cruise.
Oh, and I’m using 64x in 2D when I’m waiting for my next mission. And NO, I’m not going to wait 1h every time my next mission is 1h away.
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“(imagine actually spending 20 min on the ground)” - doing all the systems checks - checking charts, what does the base look like, which way is the runway, which taxi way do I need to follow - warming up the MAVs having blown the caps - warming up the TGP - starting TFR - double checking STP’s altitudes and timings - listening to ATIS - setting barro pressure - setting HSI bearings to pick up the outgoing radial - checking ILS stuff - setting/checking TACAN frequency - hot pit refuel if required - checking neutral trim - checking in with Ground Control - pulling the EPU pins - removing chocks - checking tanker frequency is correctly set on U13… all that stuff fills my 20mins no problem ;0) and that’s flying with AI’s, when flying with humans the list is much longer as there are all the IDM checks to make and all the radio checks to call in as well as light sequencing so every one else knows the state of your jet.
If your just going to “zoom and boom” then probably 20 mins is a long time to sit and wait.
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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.
I think I have experienced others but I can’t say with any specificity about them. Time accel shortening the useful motoring time was a surprise but it’s not a large practical obstacle. I’ll keep a look out for things which have an effect going forward to isolate.
Does anyone have a list of items that can mess with JFS? So far I have canopy and time x. I had a strong suspicion air source could cause premature overheat but in testing seems to be non factor.
As for someone’s question, time accell should have no effect if you are 1x between clicking start2 and 55% rpm. The worst situation seems to be a shortening of the time window at 4x or more. If you don’t delay starts at even 8x may be possible.
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“(imagine actually spending 20 min on the ground)” - doing all the systems checks - checking charts, what does the base look like, which way is the runway, which taxi way do I need to follow - warming up the MAVs having blown the caps - warming up the TGP - starting TFR - double checking STP’s altitudes and timings - listening to ATIS - setting barro pressure - setting HSI bearings to pick up the outgoing radial - checking ILS stuff - setting/checking TACAN frequency - hot pit refuel if required - checking neutral trim - checking in with Ground Control - pulling the EPU pins - removing chocks - checking tanker frequency is correctly set on U13… all that stuff fills my 20mins no problem ;0) and that’s flying with AI’s, when flying with humans the list is much longer as there are all the IDM checks to make and all the radio checks to call in as well as light sequencing so every one else knows the state of your jet.
If your just going to “zoom and boom” then probably 20 mins is a long time to sit and wait.
Actually, 20 min is pretty quick based on my experience launching RL jets. I’ve seen jets take 45 min to get out of the chocks, depending on what they are doing, and if any troubleshooting is required. Which is why the JFS shutdown at 4 min is more than appropriate. Yes - there’s a lot of stuff to get done before leaving the chocks, but it can be done on internal power.
As to MAVs - blowing the covers on the desk with ground personnel in the area is highly irregular, if not downright dangerous - which is probably another good reason that US forces have quit using the triple racks, and installing the dome covers pre-launch.
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Actually, 20 min is pretty quick based on my experience launching RL jets. I’ve seen jets take 45 min to get out of the chocks, depending on what they are doing, and if any troubleshooting is required.
Usually, BMS puts you in the pit 21 min before takeoff.
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“(imagine actually spending 20 min on the ground)” - doing all the systems checks - checking charts, what does the base look like, which way is the runway, which taxi way do I need to follow - warming up the MAVs having blown the caps - warming up the TGP - starting TFR - double checking STP’s altitudes and timings - listening to ATIS - setting barro pressure - setting HSI bearings to pick up the outgoing radial - checking ILS stuff - setting/checking TACAN frequency - hot pit refuel if required - checking neutral trim - checking in with Ground Control - pulling the EPU pins - removing chocks - checking tanker frequency is correctly set on U13… all that stuff fills my 20mins no problem ;0) and that’s flying with AI’s, when flying with humans the list is much longer as there are all the IDM checks to make and all the radio checks to call in as well as light sequencing so every one else knows the state of your jet.
If your just going to “zoom and boom” then probably 20 mins is a long time to sit and wait.
4x (until ready to taxi) is usually enough to do what’s mentioned in the manual, except listening to ATIS.
There are some things you mentioned that I don’t do. For example, I don’t check the charts (I use sattelite cam to see where I am). Using a tanker is pretty pointless in KTO, the tanker is often not much closer to the frontline than home plate. I don’t use ILS and TACAN. I don’t double check STP’s altitudes and timings (I usually ignore them anyways).
I probably prepare less and do more risky stuff than one would IRL.
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4x (until ready to taxi) is usually enough to do what’s mentioned in the manual, except listening to ATIS.
There are some things you mentioned that I don’t do. For example, I don’t check the charts (I use sattelite cam to see where I am). Using a tanker is pretty pointless in KTO, the tanker is often not much closer to the frontline than home plate. I don’t use ILS and TACAN. I don’t double check STP’s altitudes and timings (I usually ignore them anyways).
I probably prepare less and do more risky stuff than one would IRL.
Instead of running x4 which breaks many things (ATC in particular for other aircrafts) just change your ramp start setting in the cfg
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4x (until ready to taxi) is usually enough to do what’s mentioned in the manual, except listening to ATIS.
There are some things you mentioned that I don’t do. For example, I don’t check the charts (I use sattelite cam to see where I am). Using a tanker is pretty pointless in KTO, the tanker is often not much closer to the frontline than home plate. I don’t use ILS and TACAN. I don’t double check STP’s altitudes and timings (I usually ignore them anyways).
I probably prepare less and do more risky stuff than one would IRL.
Treat you Sim Life as you would your Real Life !!!