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Capacitive Fuel Tanks Worth The Work?

CharlieWaffles

CharlieWaffles

Well Known Member
Has anyone used Capacitive fuel sensors rather than the stock floats? How hard was it to put them in and would you do it again? Is it worth the effort? I hate the unreliable, bouncing numbers of floats in a plane. I've always hated that in planes I've flown before and always wondered why they didnt come up with something better.
 
I have the cap sending sytem in my RV9. The install is very easy and works well with my IK Technologies engine monitor. The only negative is that the sending units (pucks) are a little pricey. I would do it again but the biplane I'm building now uses a Stearman type site glass to indicate fuel quantity. Low tech.
 
You have to have a converter in between the probes and the EFIS. You can use the Dynon converters. They are the least expensive. My EI converters were $130 each. I don't recall the price of the Dynon converters, but they were substantially cheaper.

Dynon part number 100654-000, $50 each.
 
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bsacks05 said:
I have the cap sending sytem in my RV9...
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Same here. Mine are connected to my Dynon EMS and work great. So good that I never bothered to calibrate my fuel flow.

AltonD said:
You have to have a converter in between the probes and the EFIS. You can use the Dynon converters. They are the least expensive...

Dynon part number 100654-000, $50 each.
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I was a Beta tester for these things and they are very accurate.

My testing was to set the wings up on sawhorses back when I was building and fill the tanks with fuel, over, and over, and over, and over again.

As I said, they work great!

The only caveat is that when installing the BnC connector in the side of your tank, make sure the entire connector is covered in proseal. Those things will leak out the center. My connectors looked like little volcanoes by the time I finished. So far, no leaks.
 
N941WR said:
. . .
The only caveat is that when installing the BnC connector in the side of your tank, make sure the entire connector is covered in proseal. Those things will leak out the center. My connectors looked like little volcanoes by the time I finished. So far, no leaks.
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Same here. Mine leaked. the good news is that the connector is accessible from the cover plate. Gooped on the proseal, no more issues.
 
I can't offer a reply specific to the RV-10, but I installed a capacitive probe in my Midget Mustang tank. I'm very happy with it and would do it again in a heartbeat.

For the first time in my GA flying career, I have a very accurate fuel gauge AND a fuel flow computer. Between the fuel flow and the capacitive gauge, I can usually estimate my fuel required for fill-up to less than 3-tenths.

Of course, I have to admit that even with 2 independent sources to derive quantity remaining, I still keep a pretty good eye on elapsed flight time between fill-ups!

FWIW
 
In a word.... no. What's the point? So you can run your tanks close to zero? Most of us have a FF transducer that when programmed correctly, will give a very accurate account of total fuel on board. You may not know what individual tank capacity is exactly, but you'll know the total within 1/2 gallon or less. If you want to push your tolerances closer than that, you may need to start another thread. My right tank float is close to accurate in level flight, and my left one reads about 2 gallons low, but I know my total, and knowing this, I will never run out of gas. If you count yourself among those that think you need dual EFIS, a second alternator to back up your battery (itself a backup), a separate power source for your second ignition system, then maybe you need the extra aggravation and expense of capacitive fuel senders. That way you are doubly sure you are about to run out of gas....
 
I installed the cap senders that Van's sells and have been 100% satisfied with system operation, very accurate from full to empty (run with EI instruments).

If you install them properly chances are slim to none that you will ever have a problem with them.
 
CharlieWaffles said:
What size/length did you order?
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IIRC I went with the 18". They are bent up to 1/8" of the tank top, then back down at about at about a 45* angle to 1/16" of the bottom. You drill a tiny hole at the very top of the bend after you are satisfied before permanent installation. You do the installation before the tank baffle install. Be REALLY careful bending as the bends need to be tight and you do not want to collapse the tubing at the bends. Use a good rolling tubing bender.
 
9GT said:
IIRC I went with the 18". They are bent up to 1/8" of the tank top, then back down at about at about a 45* angle to 1/16" of the bottom. You drill a tiny hole at the very top of the bend after you are satisfied before permanent installation. You do the installation before the tank baffle install. Be REALLY careful bending as the bends need to be tight and you do not want to collapse the tubing at the bends. Use a good rolling tubing bender.
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Are the associated electronics accessible from a service point if there becomes an issue? complete replacement would be hard, but I wonder if the "advanced" version they sell would be better so the electronics are more available.

So for yours, aircraft spruce wants to know the bendable length (NB, 3, 5) and mounting (I'm assuming Flange).

http://www.aircraftspruce.com/catalog/inpages/princefuelprobes.php
 
CharlieWaffles said:
Are the associated electronics accessible from a service point if there becomes an issue? complete replacement would be hard, but I wonder if the "advanced" version they sell would be better so the electronics are more available.

So for yours, aircraft spruce wants to know the bendable length (NB, 3, 5) and mounting (I'm assuming Flange).

http://www.aircraftspruce.com/catalog/inpages/princefuelprobes.php
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There are no electronics to access,,,,its all encased in a cast composite. You replace the unit in the very unlikely case one would fail. Not a big deal. No more so that replacing a typical float.
 
Fuel Sendors

From the research i have done on this,i think the easiest and cheapest way to go is the Vans kits and make two new aluminum plates to fit the -10 ribs and go from there, the bnc connector idea is very simplistic no parts to go bad and very easy to install. There is no need to to a probe install from ACS. Vans sells a kit for the -9 that will work perfectly and no issues from what I have seen.

Being a Flight Engineer for 14 years before i retired from the Air Force, having Accurate fule avaulable is a safty of flight deal for me. There are way to many viariables when flying that knowing on a quick glance what is available is critical.

Just using a flow meter is not accurate enough when a problem happens.

Once coming back from Japan out over the Ocean at night we had a dump valve start leaking and we did not fine it for about a hour and we lost alot of fuel in the process. The Fuel flow showed the correct fuel burn but the fuel gauges showed what was really left in the tanks. We deverted to Shemya Island out at the end of the Alaska Alutian Chain of islands and got feul and fixed the leak.

If it was not for the hourly readings and compairsion between actual available and what should be available that every flight engineer does, we would of never discovere the lak and we could of been in real trouble.

So having accurate fuel gauges is very important.

Fuel leaks do happen quiet offen. Even a sump valve can dump a half a tank in a very short time and being on the bottom of the wing you would not even know it.

So my vote is do some research, there are several web sites showing the install for the Vans Kits in the -10 fuel tanks, order the kit and go for it.

John Cumins
40864 Emp done wings, rear spar inprogress:)
 
jc11378 said:
From the research i have done on this,i think the easiest and cheapest way to go is the Vans kits and make two new aluminum plates to fit the -10 ribs and go from there, the bnc connector idea is very simplistic no parts to go bad and very easy to install. There is no need to to a probe install from ACS. Vans sells a kit for the -9 that will work perfectly and no issues from what I have seen.
So my vote is do some research, there are several web sites showing the install for the Vans Kits in the -10 fuel tanks, order the kit and go for it.
John Cumins
40864 Emp done wings, rear spar inprogress:)
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I thought about doing the Vans kit adaption but decided against it. When I emailed Vans support with the idea of using their home brewed sender they pretty much said not to. The one main feature of using the Princeton 5 point set capacitance probes are for the accuracy. The 5 point set helps to give a more accurate reading on the actual fuel in the tank because of the varying level of fuel due to the wing dihedral. Nothing wrong with rolling your own. I installed the standard 2 point set on the Cozy MKIV because the tanks are level. The accuracy is amazing.
 
Redundancy

All of the military aircraft I have flown have used float type units for quantity and a separate binary capacitance type for low fuel...light comes on once it is uncovered, you place it near the bottom with X amount of gallons remaining. We have always just assumed that fuel quantity is approximate and never plan to land with low fuel, but if the "low fuel lights" come on, you KNOW you are low.

Is there any type of small, simple low level sensor like this out there for GA?
 
I'll probably regret this post someday but.......:rolleyes:

I did the capacitive sensors and did NOT cut the big access hole in the inboard rib. I didn't want to build in a useless leak path. I figured if I had a leak, the access hole would not be where I needed it anyway so I girded myself to cut the rear baffle if needed. All OK so far.

I used the Dynon capacitance to voltage convertors noted earlier in the thread. They work fine for me. The trick was figuring out the Y=MX+B numbers for the EIS 4000. Brantels basic data charting work was critical to my success there.
 
In follow up, now that I am flying, in hindsight I should have just gone with floats. The capacitive senders work fine, but they don't measure anything about above 20 gallons in the tank due to the dihedral in the wing. And below there they are just as accurate as floats.
 
It would seem that the floats would do the exact same thing. When the float is all the way up, there is still a lot of fuel "above" it in the wing due to the dihedral. So it won't really read correctly until it begins to drop.

The capacitive probes are the same, correct?

To me, it is more important to measure the quantity when near empty rather than near full but my question is, "Is there a way to get an accurate measure from Full to Empty with any kind of sender?". My biggest condition is that the fuel tanks are already built so running a capacitance probe the complete depth of the tank is out...

Anyone?

Bueller? Bueller?
 
Capacitance probes read high?

I was busy installing Van's capacitance probes when I read that if you calibrate the probes for Avgas they will read high for fuel containing EtOH. That seemed like a safety issue to me, so I went with the floats.
 
yeah, ran across your build earlier. I have the QB tanks, so there is no way to span several bays.

Doesn't really matter, though. I am comfortable with fuel flow, totalizer, and gauges that read the last 20 gallons...

Couple that with the fact that the capacitance probes are already pro sealed in, well, I guess I'm good to go...
 
I have found I closely watch the fuel computer consumption more than anything else - it is usually within .1 gallons of my actual usage. So the fuel gauges have become a backup and are there to remind me which take may be lower than the other, etc..
 
Cap. Fuel Indication

Well i went with the Vans kit. It was very cheap. I then made new plates to fit the rv-10 rib.

I will have very accurate indication since one plate is i bay from the filler opening and the other is 1 bay o/b from the i/b lowest bay.

Probe type sensors are not accurate enough due to they do not span the entire tank from the highest point of the tank by the filler opening to the lowest point at the fuel pick point.

The plate style does as close as can be.

It was very easy to install the 2 plates the bnc connector was very easy to install and seal up.

So if any one wants to contact me feel free my email is [email protected]

I have alot of pics available.

One thing i did was add a additional mount screw where the vans lit onkly has you install 3 per plate. I used 2 mount points on the fwd part of the plate and 2 on the rear part of the plate.
 
+1 for the "plate" cap set up

Just like John, I installed the Van's cap system, but made custom-sized plates to fit the 10 (Vans doesn't currently offer them for the 10). I'm not flying yet, but I believe they will offer accurate measurements from full to empty (or close to it).

However, I also installed float senders. The place for the floats is incorporated into the rib in the 10 kit, not mounted to the coverplate like in the other models, so my choice was either cover the holes or install the float senders too. I figure the added weight is minimal and it's nice to have the backup, should the cap senders not function adequately. My $0.02.
 
Yes, but

rocketman1988 said:
but my question is, "Is there a way to get an accurate measure from Full to Empty with any kind of sender?".
Anyone?

Bueller? Bueller?
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In the T-6 we have multiple sensors that overlap (low for one is high for another) then they are integrated into the digital FMS for a nice smooth quantity display output. A nice long slip can confuse them, but otherwise they are great...but I think this is probably WAY outside the budget for an RV :D
 
Here's an off-the-wall thought... Has anyone tried finding a pressure sensor that would accurately measure from 0-12 (ish) inches of water? One sensor mounted at the bottom corner of the tank near the fuel exit would let you measure pressure due to the depth of the fuel in the tank?

Of course, the reading would only be valid in coordinated flight, at 1G, etc... No worse than a float, mind you. But it would read right from full to empty?
 
Snowflake said:
Here's an off-the-wall thought... Has anyone tried finding a pressure sensor that would accurately measure from 0-12 (ish) inches of water? One sensor mounted at the bottom corner of the tank near the fuel exit would let you measure pressure due to the depth of the fuel in the tank?

Of course, the reading would only be valid in coordinated flight, at 1G, etc... No worse than a float, mind you. But it would read right from full to empty?
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I don't think it would work on our tanks, as they are vented and get some ram air effect which will vary the pressure in the tanks depending on airspeed and AOA. I would imagine this changing pressure would cause the probes to read erratically.

There is a company that makes a pressure based fuel probe, but it will only work on non-vented tanks:
http://www.beliteaircraftstore.com/liquid-level-fuel-probe-with-1-4-probe/


All that said, I'm thrilled with my capacitive sensors. I bought the Van's RV9 kit and made my own larger plates, and used the Princeton cap converter boxes (with one set point) from Stein. The Cap Converter gets calibrated at empty, the calibrate the tanks on the Garmin just like you would with a float. Mine reads all the way from full to empty, quite accurately, with calibration points every 2 gallons.
 
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I guess you could call me an early adopter of the capacitance fuel level senders since I was one of Dynon's first beta testers.

I was testing them before the plane was even together by putting both wings on sawhorses and running wires across the shop to my D10 EMS. Using the Dynon senders, which I still have, and Van's plates I was able to tilt the wings, drain them, add fuel, etc. I have tested them down to empty and flown with them down to 1.5 gallons in each tank. (While that sounds reckless, it was 45 minutes of fuel back when I had the O-290-D2 installed.)

I have learned to trust the capacitance senders more than I trust my fuel flow. Those things are spot on!

Thank you Dynon and Van's for making such accurate fuel gauges!

PS. They may have an issue going back and fourth between 100LL and MOGAS, but I really don't know as I have never run MOGAS and if I get in a pinch and need to, I always have my fuel flow / usage to look at.
 
NovaBandit said:
I don't think it would work on our tanks, as they are vented and get some ram air effect which will vary the pressure in the tanks depending on airspeed and AOA. I would imagine this changing pressure would cause the probes to read erratically.

There is a company that makes a pressure based fuel probe, but it will only work on non-vented tanks:
http://www.beliteaircraftstore.com/liquid-level-fuel-probe-with-1-4-probe/


All that said, I'm thrilled with my capacitive sensors. I bought the Van's RV9 kit and made my own larger plates, and used the Princeton cap converter boxes (with one set point) from Stein. The Cap Converter gets calibrated at empty, the calibrate the tanks on the Garmin just like you would with a float. Mine reads all the way from full to empty, quite accurately, with calibration points every 2 gallons.
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If it were going to have any chance of working, it would have to be a differential pressure sensor, one side at the bottom of the tank, one connected to the vent. In the liquid rocket engine testing world we used this method for gauging stationary tanks, even pressurized ones, but if you were to try it on a moving vehicle, you'd have to compensate for acceleration, and it would get very complicated very fast.
 
longranger said:
If it were going to have any chance of working, it would have to be a differential pressure sensor, one side at the bottom of the tank, one connected to the vent. In the liquid rocket engine testing world we used this method for gauging stationary tanks, even pressurized ones, but if you were to try it on a moving vehicle, you'd have to compensate for acceleration, and it would get very complicated very fast.
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Float-type senders would have to compensate for acceleration as well, so I don't think it would be any worse. You'd care more about the reading in level, stabilized flight... and would have to keep in mind that the reading would change in climb or descent, as with a float.
 
Snowflake said:
Float-type senders would have to compensate for acceleration as well, so I don't think it would be any worse. You'd care more about the reading in level, stabilized flight... and would have to keep in mind that the reading would change in climb or descent, as with a float.
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The problem is much worse with the pressure sensor. In a level 60 deg banked turn (2 g) the float will 'feel' twice as heavy. But it's light to start with, so it will only sink a little bit extra, so it will read slightly low. But the differential pressure gauge will be a full 2x higher.
 
BobTurner said:
The problem is much worse with the pressure sensor. In a level 60 deg banked turn (2 g) the float will 'feel' twice as heavy. But it's light to start with, so it will only sink a little bit extra, so it will read slightly low. But the differential pressure gauge will be a full 2x higher.
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Agreed, but you don't typically *stay* in a level 60 degree banked turn for very long, and even if you do you probably don't stare at your fuel gauge the whole time. Fuel gauges really only need to be useful in 1G, level flight. Turbulence may have an effect, but i'd expect that some kind of damping on the pressure readout would average the bumps out to something close to the nominal value anyway.

The only gauges that would read the same regardless of attitude might be the capacitive type, I guess? Or gauges that infer fuel level based on fuel flow only, which is what I would give serious consideration to were I ever to take my fuel system apart for a major refit.
 
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