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Jetcat low fuel warning system

Old 10-29-2009, 10:10 AM
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seflyer
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Default Jetcat low fuel warning system

has anyone been using the low fuel warning system in the Jetcat ECU? from what I read it lowers the throttle for a few seconds and then returns to set position and reapeats at a set interval.

I want to try it out on my PST Reaction with 120 as I get 7 minutes at full throttle but when flown with mixed throttle can land with as much as 1 1/2 liters left on board. just looking to see if anyone has used it it with any degree of success.

thanks Kevin
Old 10-29-2009, 10:12 AM
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Default RE: Jetcat low fuel warning system

I bet everyone's like me Kevin, daren't risk using it!
Old 10-29-2009, 10:20 AM
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seflyer
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Default RE: Jetcat low fuel warning system

I do not think I'll risk it on a heavily loaded jet like my F-16, but for something like the reaction I think it would be ok, it can be overidden at any time by lowering the throttle to idle and return to set position. the only reason for wanting to use it is my varying amonut of fuel burn from flight to flight.


Kevin
Old 10-29-2009, 10:27 AM
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Default RE: Jetcat low fuel warning system

I've been a bit dubious about using it I guess because I am fairly new to Jets but now I have 65 flights on my Sprint I think I'll give it a go.
I remember that initially I dare not set it in case it failed to work (unlikely I now know with Jetcat) and I would have been forced into my first jet deadstick.
However, after a recent really enjoyable flight I was having so much fun I failed to hear my timer and flamed out. The landing was great so maybe I'll set it up and give it a go.
I am just finishing off an FEJ F16 with a new 80SE by the way, I'll need to pick yuor brains again before I test fly!
Gary.

Old 10-29-2009, 10:27 AM
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Default RE: Jetcat low fuel warning system

use timers.

my 2c
Old 10-29-2009, 10:35 AM
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seflyer
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Default RE: Jetcat low fuel warning system

I use my timers at 7:30, this is fine if I fly full throttle the whole flight, which is common for me, 3.5 liters on board. if I fly mixed throttle I can go 7:30 and still have 1 to 2 liters on board because I have no idea of where the level is so this is why I am contamplating using it. the reaction seems the safest plane to test it on right now.

Kevin
Old 10-29-2009, 10:51 AM
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Guillermo Ibanez
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Default RE: Jetcat low fuel warning system


ORIGINAL: seflyer

has anyone been using the low fuel warning system in the Jetcat ECU? from what I read it lowers the throttle for a few seconds and then returns to set position and reapeats at a set interval.

I want to try it out on my PST Reaction with 120 as I get 7 minutes at full throttle but when flown with mixed throttle can land with as much as 1 1/2 liters left on board. just looking to see if anyone has used it it with any degree of success.

thanks Kevin
Jet Cat low fuel warning has two options in the ECU:

One is to lower the throttle, which to me is very risky, and the othe is to send a signal to smokepump to make smoke trials at intervals. If you don't have a smoke pump, you can connect a bright LED to the smoke pump connector on the ECU and have this LEDin a position on the model, you can see from the ground.

When the ECU reahc the fuel capacity set in the tanks, it will lit the LED. Of course you need to set the alarm at a % of the total fuel set at the ECU.

Go to this thread:

http://www.rcuniverse.com/forum/m_90..._1/key_/tm.htm

BRG
Old 10-29-2009, 12:17 PM
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digitech
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Default RE: Jetcat low fuel warning system

it lower the throttle very fast and up again , if you dont think about it it feels like a signal drop..
but it does work ok.

as for the led also good idea but you need a VERY bright one..
Old 10-29-2009, 12:58 PM
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Default RE: Jetcat low fuel warning system

Yes, I have used it.

It has a serious flaw, at least on my 5.0 ECU, which I hope was corrected on later ECU versions (?)

The ECU computed burns are only 50-75% of the actual burns, varying wildly. I might have experimented with the system and "lied" to it about how much fuel was on board in order to get it to activate at the right time, if the only issue were accuracy. But the fact that the amount of error varied from flight to flight made the feature unusable in my case.

I have meant to call JC to ask about the inconsistency/errors but haven't gotten around to it.

That being said, I think that the LED option (which is on newer ECUs but not mentioned in my manual) is a MUCH better idea than a throttle blip. If the throttle blips at the wrong time u are screwed, screwed, screwed. My system did activate once because I did not turn off the ECU (which resets the burned values back to zero) between flights once. I got the blip with about 3/4 of my fuel left on the second flight because the ECU was fooled into thinking I had not refueled and was still adding to the previous flight's burn values. CRAP ! I thought the damn thing had quit, but then I moved the throttle and it was running fine. Then I thought it quit AGAIN, until I cycled the throttle and got it back.

If I had not been flting a very lightly loaded jet (as suggested in a post above) I could have easily lost it.
Old 10-29-2009, 01:45 PM
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Default RE: Jetcat low fuel warning system

ORIGINAL: highhorse

I have meant to call JC to ask about the inconsistency/errors but haven't gotten around to it.

it gets its fuel flow guesstimate from averaging the fuel pump voltage and the fuel system doesn't have the same resistance to the fuel pump the entire flight (this is also why you have varying max pump voltages from flight to flight). every time you pull/push G's the gravitational effects of the fuel can starve/flood to the pump and cause inconsistencies between voltage in and fuel out.
Old 10-29-2009, 02:01 PM
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Default RE: Jetcat low fuel warning system

I don't think G's would be much of an issue in my app because the tanks are approx level with the pump. Perhaps extended up lines would increase the pump load ?

But u bring up an excellent point (as always).

I have two tanks, in series. Both have felt clunks (large and in good condition, don't worry). The draw resistance must be MUCH less for the second half than the first half of the flight, varying the voltage. But then again, extra resistance should mean an OVER estimated burn, not under.

Hmmmmmm. Either way, too many variables for me, in my app, to make it work.
Old 10-29-2009, 02:08 PM
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Default RE: Jetcat low fuel warning system

just wondering why can't the system just lower the gear. Having a light or having the throttle spool the engine up and down just doesn't seem the best idea, I persoanlly would have a problem seeing the light or maybe hearing the engine spool up and down, but could see the gear lower, and since you're getting low on fuel might as well land....the gear is already out.
Old 10-29-2009, 02:39 PM
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Default RE: Jetcat low fuel warning system


ORIGINAL: jeteffx

just wondering why can't the system just lower the gear. Having a light or having the throttle spool the engine up and down just doesn't seem the best idea, I persoanlly would have a problem seeing the light or maybe hearing the engine spool up and down, but could see the gear lower, and since you're getting low on fuel might as well land....the gear is already out.
On a 199.99 mph burnin' low pass and gear and doors pop out? Ouch!

Kevin, like said above even in your reaction, a change in throttle at certain times can kill your reaction.

Kinda like you said, if you fly pedal to the metal, then you know how much time you've got left.

When we are "hill climbing" I make SURE to land at least 1 minute early and I don't mess around with that! Sometimes I don't even trust that I can do a gear pass and then land, its straight to gear, flaps and land all on the downwind!

Raf

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