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06-19-2019, 11:07 PM
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Join Date: Aug 2015
Location: Grand Prairie, TX
Posts: 13
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Capacative fuel gauge senders.......... Huh ?
I'm still a builder, and not yet a pilot (saving that for the last year of the build).
Anyway, in finishing up the prep work on the fuel tanks I see this note that says, "If you plan to use the capacative fuel tank senders offered in the accessories catalog, you should do that now".
Problem is, I don't know what that is (I mean, I have an idea, but not if I NEED it or not), and second, I can NOT find this in any keyword on the catalog.
So, DO I need it? And if I do, how to find it on the catalog ?
Appreciate the help
__________________
Andrew
RV-10 Wing Kit - In Progress (Started 05/10/18)
RV-10 Empennage - Completed
08/08/15 N813AL Requested
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06-20-2019, 01:26 AM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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With a capacitive sender, you build a capacitor (think two parallel plates) into the tanks. The tank is one plate, you build the second ‘plate’ into the tank. As the space between them is filled with fuel, the dielectric constant changes, so the capacitance changes. You calibrate the capacitance vs the amount of fuel. Properly done, they are very accurate.
No you don’t need one. The stock float gauges, calibrated thru an EFIS, are quite accurate except they can’t see the top 5 gallons. And, for good engine management, you also really want a fuel flow gauge. They can tell you how much gas is left to very good accuracy.
Edit. Think about speeding up the Private pilot rating. Things change with time, but today, if you approached an insurance company with typical 1 year’s experience for insuring a 10, be prepared for sticker shock.
Last edited by BobTurner : 06-20-2019 at 01:30 AM.
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06-20-2019, 05:50 AM
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Join Date: Oct 2014
Location: Milwaukee, WI
Posts: 300
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Quote:
Originally Posted by BobTurner
With a capacitive sender, you build a capacitor (think two parallel plates) into the tanks. The tank is one plate, you build the second ?plate? into the tank. As the space between them is filled with fuel, the dielectric constant changes, so the capacitance changes. You calibrate the capacitance vs the amount of fuel. Properly done, they are very accurate.
No you don?t need one. The stock float gauges, calibrated thru an EFIS, are quite accurate except they can?t see the top 5 gallons. And, for good engine management, you also really want a fuel flow gauge. They can tell you how much gas is left to very good accuracy.
Edit. Think about speeding up the Private pilot rating. Things change with time, but today, if you approached an insurance company with typical 1 year?s experience for insuring a 10, be prepared for sticker shock.
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When shopping for insurance on our partnership we were told that most companies want 300 hours total time for insuring a pilot in a 10. One of our pilots didn't have that. Sticker shock was an appropriate term.
__________________
Matt
CFI / RV-10
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06-20-2019, 05:59 AM
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Join Date: Mar 2016
Location: Northern VA
Posts: 267
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I'm not sure VANS is selling the capacative kit anymore (at least I couldn't find it when I was looking a few months ago). Not sure what the story was.
But as Bob pointed out, it's just a different way to measure how much fuel is in your tanks with no moving parts. Downside from what I understand is changes in fuel (100LL to MoGAS or Swift) would require a re-calibration of your fuel gauges due to differences in electrical resistance of the fuels.
Another thing to think about is installing a return fuel line. It's not absolutely needed, but so much easier to install while building the tank than after the tank is finished.
__________________
Brian Lester
Dues Paid - 2020
RV10 Slow Build - #41778
Finish Kit - in progress
RV10builder.com
KVKX / KHEF
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06-20-2019, 06:09 AM
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Join Date: Aug 2015
Location: Grand Prairie, TX
Posts: 13
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Thank you all for the excellent feedback....
BrianDC, what is the purpose for this return fuel line? I assume it's in the 'intake' fuel line, what is the need for it to not be there?
__________________
Andrew
RV-10 Wing Kit - In Progress (Started 05/10/18)
RV-10 Empennage - Completed
08/08/15 N813AL Requested
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06-20-2019, 06:30 AM
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Join Date: Mar 2016
Location: Northern VA
Posts: 267
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Quote:
Originally Posted by TXHardWorker
Thank you all for the excellent feedback....
BrianDC, what is the purpose for this return fuel line? I assume it's in the 'intake' fuel line, what is the need for it to not be there?
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Depending on your engine and fuel system setup, you may not need a fuel return line.
Some fuel injection systems have the ability to recirculate fuel back to the fuel tank. This has a benefit for hot starts as the fuel lines shouldn't experience vapor lock. Downside is fuel line plumbing gets a little more complicated.
__________________
Brian Lester
Dues Paid - 2020
RV10 Slow Build - #41778
Finish Kit - in progress
RV10builder.com
KVKX / KHEF
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06-20-2019, 06:43 AM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Quote:
Originally Posted by BrianDC
Depending on your engine and fuel system setup, you may not need a fuel return line.
Some fuel injection systems have the ability to recirculate fuel back to the fuel tank. This has a benefit for hot starts as the fuel lines shouldn't experience vapor lock. Downside is fuel line plumbing gets a little more complicated.
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You can accomplish this without plumbing the return all the way back to a tank. I have the AFP FI system with purge valve and my return is plumbed back to just below the fuel selector valve.
The simplest and easiest plan is to stay as close to the plans as possible. Most of the mods that you'll learn about are builder preference or "nice to haves" that simply aren't necessary and won't make the plane fly any better.
__________________
Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
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06-20-2019, 06:54 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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For clarity, some fuel systems *need* a return line to a (or both) tanks. Most of the automotive style injection systems (SDS, etc) need them. It's optional with 'traditional' dribble injection systems (Bendix, etc) to clear hot fuel from the engine compartment prior to start. If you think you'll ever have an injected engine, planning for a return line now (at minimal pain/expense) will make life a lot easier later.
Capacitive level sensors have the downside that their calibration changes with fuel type. If you never expect to run anything but 100LL, it doesn't matter, but any auto fuel and likely any future no-lead aviation fuel will have a different capacitance, and will therefore affect calibration of the sensors. Switching among or mixing the various fuels (likely to happen frequently in the future, as we transition off 100LL) will cause changes in calibration.
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06-20-2019, 08:33 AM
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Join Date: Feb 2015
Location: Locust Grove, GA
Posts: 621
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Take a look at the RV14 fuel tanks. Virtually identical to the RV10 and they were designed with a fuel return fitting. Really easy and inexpensive to buy and install the parts when building the tanks. It?s what I did with mine for return lines required by the SDS fuel system design.
__________________
Krea Ellis
Locust Grove, GA
DA20-A1 "Princess Amelia" - gone home to Amelia Island
RV-7A Phase 2
RV-10 under construction at Synergy Air South
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06-20-2019, 09:15 AM
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Join Date: Aug 2018
Location: Bell, FL
Posts: 387
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Dielectric constant
I didn't install the plates in my RV-4 tanks for the reason Charlie gave (MoGas dielectric constant change with "summer"/"winter" fuel and alcohol content).
Now I regret it. I think that by installing a separate plate near the bottom inboard skin of the tank that's always covered by fuel, one would have a reference capacitance that could be used to correct the output. I realize that there's probably no capacitance-to-voltage-converters (you'll need one if installing the capacitive fuel gauge senders) on the market that have a such a reference input, but I'd have built them myself.
I understand that Van's kit is (was) a plate mounted next to the outboard rib and a plate mounted next to the inboard rib (the two plates wired together), so as to be able to sense from full to empty. In my old RV-3 I made a tube within a tube (with insulating spacers) that ran through holes in the ribs from inboard lowest point to outboard highest point. Outer tube had holes at regular intervals for fuel to enter. That gave a continuous reading from full to empty.
More than you probably ever wanted to know
Finn
__________________
N214FL RV-4 -- Building
N46AZ RV3-B Mazda 13B EFI -- Bought -- Flying
N993FL RV-3A Mazda 13B NA 575 hours
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