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Author Topic: JetProp Low Fuel Light  (Read 2475 times)

donv

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JetProp Low Fuel Light
« on: May 03, 2016, 02:17:43 pm »
I got to experience the Low Fuel light in the 980 the other day, a first for me. As I mentioned in another thread, I've had some difficulty in getting full fuel, although it comes close. The other day, I was returning home and the weather was clear, lots of alternates around, and it seemed like the perfect time to stretch the fuel a bit and see how she behaves.

I planned to arrive with around 500 pounds, and about 10-15 miles out, the Low Fuel light came on, which indicates 150 pounds or less on one side. The procedure for Low Fuel light is to turn on the Low Fuel pumps, which scavenge fuel from the outer bladders into the feeder.

The thing to know about the Low Fuel pumps is that, once you turn them on, the Low Fuel light may go out (it only flickered in my case), and the indicated fuel quantity will increase. Of course, this doesn't mean you actually have more fuel, just that it looks like you have more fuel.

When I shut down, the fuel gauges showed 300 pounds on one side, and 200 pounds on the other. However, I think that's more than I actually had due to the indication issue I mentioned above.

The other thing to know about fuel in a turboprop is that you really don't use all that much less in the descent than you do at cruise at altitude, and certainly any savings you might realize are more than used up during any low altitude maneuvering. So don't count on burning less as you start down.

Steve binnette

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Re: JetProp Low Fuel Light
« Reply #1 on: May 04, 2016, 12:06:59 am »
I had some wind a week ago that had me land short for fuel.  I had planned to go from St. Louis straight to Camarillo ca.  It was about 1400 nm. 

As I approached Las Vegas I got nervous and dropped in for fuel.  It was a 5.1hr leg and I landed with 800lbsafter some vectoring around.

My Garmin was showing I would land in CMA with 550lbs.  As I get more comfortable with the plane I might  stretch it a little more. Right now 800lbs is comfortable.

Adam Frisch

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Re: JetProp Low Fuel Light
« Reply #2 on: May 04, 2016, 01:32:01 am »
Good move. It always take's a little time to build up the confidence in them. 550lbs should be about 1,5hrs in cruise, right? If it was VFR, that'd be comfortable from LAS, but you don't want to take chance of any marine layer, alternate stuff… Still, very impressive the Commanders - that's a long a** routing. Not many TP's can go direct from St Louis to NV.
Slumming it in the turboprop world - so you don't have to.

Steve binnette

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Re: JetProp Low Fuel Light
« Reply #3 on: May 04, 2016, 10:22:54 am »
I am using 600lbs as an hours worth of fuel on arrival.  That is a worst case scenario if forced down low. 

At cruise my burn has been about 460lbs per hour. 68.6/gph

donv

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Re: JetProp Low Fuel Light
« Reply #4 on: May 04, 2016, 11:34:32 am »
800 pounds is a good number, IFR, and 600 pounds is certainly reasonable VFR. I will run it down to 500 pounds if the weather is clear, although given my most recent experience, I'm less confident about that.

Funny, I was in St. Louis last week as well! St. Louis Downtown (KCPS), in my case.

Adam, I burn about 420 pph at FL280 at cruise, but down low, 500pph is pretty reasonable. I imagine the 680V burns a little less per hour, but of course is going slower. And, if it's similar to a 690, it probably has a less accurate fuel gauging system.

One thing about the Jetprops is that they really went back to the 690 customers and did a lot of research on what things they didn't like-- and one of them was the fuel gauging, which is notoriously bad in a 690. So they went with a much more accurate system, and it works great.

Adam Frisch

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Re: JetProp Low Fuel Light
« Reply #5 on: May 04, 2016, 09:21:51 pm »
I'm not going to trust the fuel gauges. I've been told the original old school totalizer is very accurate, though, so I'm hoping I can rely on that. My friend Stan burns about 54-58gal/hr at 96% rpm at 17000ft, doing about 245kts. So I'm hoping to be in that region. But I only have 337gal in total, not 474gal like you guys, so my range is much more limited. You can hang the slipper tanks on and get to 437gal, but then I'd better be alone and naked, or I'm overweight... :o
Slumming it in the turboprop world - so you don't have to.

Bruce Byerly

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Re: JetProp Low Fuel Light
« Reply #6 on: May 14, 2016, 09:02:16 pm »
Adam, if you can, have the plane defueled and calibrate the system so you know exactly how much it holds in today's world.  Then, when you verify it's topped, you can get to know the totalizer and whether or not it is accurate.  Most should be accurate to the pound.  As long as you start full or with the center full, you should know exactly how much fuel you have via the totalizer which is the most accurate fuel measuring system in any plane which I have flown.  Not sure if the pre-690 planes used the same system or not but that would be easy to figure out. 

Adam Frisch

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Re: JetProp Low Fuel Light
« Reply #7 on: May 14, 2016, 09:08:32 pm »
Bruce, it's the little Foxcom (is that the name?) unit that ticks away like an odometer - is that the same you guys have in the 690? I know mine is the same as in the 681 and Stan says his is very accurate.

I'll ask Morris to defuel plane for me, calibrate fuel etc once engine runs are done.
Slumming it in the turboprop world - so you don't have to.

Bruce Byerly

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Re: JetProp Low Fuel Light
« Reply #8 on: May 15, 2016, 12:33:32 am »
Yessir.  The Foxboro8) Don't know the Foxboro folks but have been putting my life in their hands forever!  Honestly it's a combination.  Your fuel gauge should certainly read accurate towards the lean end.  I'm not sure what good the fuel gauge is above 1,000 lbs anyway. You'll get used to it.  For example, if I run it normally, I know the 500B will go 5 hours and should be looking right at a runway.  I also believe that it's a few gallons short on the fillip test.  Not sure where they went, but I'm not pushing those last few gallons and so will always aim to land with 30 remaining assuming good weather, etc. - that's my limit.

 I continually track the totalizer burn vs. the gauge and the actual gallons put into the plane.  So I really have confidence though I will admit to making a fairly quick landing the other day after sun n fun when my gauge started acting up. Turned out everything was right on the money, I had exactly what I thought, and we moved on.  Of course the big thing with Commanders which is related to this topic is making sure the line fills up the plane.  They are slooow filling at the top. It used to be almost everytime the city fueled the 500 I would have to call them back to put the last 5-10 gallons in the plane.

ghancock

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Re: JetProp Low Fuel Light
« Reply #9 on: May 15, 2016, 10:22:12 pm »
Yeah, I had this happen to me just yesterday at Double Eagle in NM.  Even after I instructed them on how to fill them up.

I have my fuel guages that I know are not accurate and I track my fuel burn through my JPI 790 which seems to be doing a pretty good job.  I'm averaging 185 kts at around 39gph LOP point to point and my fill ups usually amount to 35-38 which is on the right side of empty for me.  I still get nervous though around 4 hours in and have to land.  Just can't fly when the gauge tells me I have 40 gallons left, even though I actually have about 80.  I wish there was a way to stick the tank or something to verify the amount of fuel actually there, but I'll just keep filling up the tanks in the mean time. :-)

Glenn
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You can't win an argument with an ignorant person,  they'll just drag you down to their level and beat you with experience.

donv

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Re: JetProp Low Fuel Light
« Reply #10 on: June 23, 2016, 01:24:12 am »
As part of my 150 hour, I had the shop do a fuel sensor calibration. The low fuel lights came on just under 200 pounds/side, which is within spec, although on the high side. I decided I'm happy with that.

Bruce Byerly

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Re: JetProp Low Fuel Light
« Reply #11 on: June 24, 2016, 04:01:30 pm »
As part of my 150 hour, I had the shop do a fuel sensor calibration. The low fuel lights came on just under 200 pounds/side, which is within spec, although on the high side. I decided I'm happy with that.

Had one where the lights functioned as you would expect but the fuel would not pump from either side but I can't recall what the failure mode was.  Kerry in Peoria might recall.  He's retiring this month so Hopefully he'll still answer the phone.  What a lifesaver he's been over the years!  It would be good to check if you are doing a fuel calibration or other work to ensure the pumps actually pump fuel.

donv

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Re: JetProp Low Fuel Light
« Reply #12 on: June 24, 2016, 08:16:08 pm »
I'm pretty sure the lights are turned out by a pressure switch. Although that doesn't guarantee anything, but it's showing you more than just power at the pump.

My right one is quite slow to come on-- sometimes it can take as much as 30 seconds.

I do know mine are pumping because, when I had the low fuel light come on, turning the pumps on caused the fuel indications to go up.