The Wizzard

The Wizzard

Well Known Member
Can anybody give me one good reason or another as why I should not use the capacitance type fuel sending units? Will they work with most of the electronic flight displays? Dynon. Is there a lot of difficulty changing them if they should go bad? Why are they not part of a quickbuild wing?
 
Different fuel types have different resistance. You will have to recalibrate if you switch between 100LL and mogas although I have never heard how much different they will read if not calibrated. With resistive you will need some extra hardware to work with most systems as you noted above. I don't think people hate either float or capacitive so I would imaging they both work well enough.
 
The Wizzard said:
Can anybody give me one good reason or another as why I should not use the capacitance type fuel sending units? Will they work with most of the electronic flight displays? Dynon. Is there a lot of difficulty changing them if they should go bad? Why are they not part of a quick-build wing?
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Cost! (Added words to comply with stupid posting rule)
 
Fuel Sending Units.

Mel said:
Cost! (Added words to comply with stupid posting rule)
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Ditto Mel's reply. Resistance units are fairly accurate, reliable and work with all types of fuel.

You should always check your fuel before take off and never EVER land with less than an hour's worth of fuel on board.:eek:

At my age, I can't hold my coffee longer anyway!;)
 
The Wizzard said:
Can anybody give me one good reason or another as why I should not use the capacitance type fuel sending units? Will they work with most of the electronic flight displays? Dynon. Is there a lot of difficulty changing them if they should go bad? Why are they not part of a quickbuild wing?
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If you are using an electronic flight display with a flow meter, that will probably be your most accurate device anyway. Fuel gauges will become secondary...
 
Flow meters are great!

flytoboat said:
If you are using an electronic flight display with a flow meter, that will probably be your most accurate device anyway. Fuel gauges will become secondary...
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I agree. The flow meter is the best device I installed after flying the plane for around six months. You know what you've used, what's left, and what it will take to get to the destination (these as connected to the GPS). Of course, fuel gauges work for leaving the fuel cap off or major leaks. A flow meter won't help in those cases.

L.Adamson --- RV6A
 
Using the Dynon capacitance senders, I didn't find the extra cost out of line. (Sorry Mel)

The thing that got me was how accurate they were. In fact, they are so accurate that this is the only plane where I actually trust the fuel gauges.

While fuel flow can be a good indication of how much fuel you have left, they won't work, if you develop a fuel leak.
 
N941WR said:
While fuel flow can be a good indication of how much fuel you have left, they won't work, if you develop a fuel leak.
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I read about a high wing that crashed short of it's destination because the fuel cap on the top of the wing had been loosened when used as a hand hold. Being a new airplane, the two pilots didn't know which to trust, the fuel flow or fuel gauge. In this case, the gauge would have been the better option.

I certainly watch my gauges, but figure fuel used...totally based on the fuel flow meter. It's always within a quarter gallon or less for accuracy.

L.Adamson --- RV6A
 
N941WR said:
Using the Dynon capacitance senders, I didn't find the extra cost out of line. (Sorry Mel)
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Maybe I'm missing something. Two Stewart Warner senders from Vans are $54. The Dynon converters are $100 and that doesn't count the fuel tank probes. To me it looks like the cost is more than double.
I have the resistance probes feeding the EI guage and find them to be very accurate.
 
L.Adamson said:
I read about a high wing that crashed short of it's destination because the fuel cap on the top of the wing had been loosened when used as a hand hold. Being a new airplane, the two pilots didn't know which to trust, the fuel flow or fuel gauge. In this case, the gauge would have been the better option.
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To paraphrase my instructor, when first learning in a C152..."these are the fuel gauges; never believe them...unless they read "empty"."

Why would anyone not land to check out a clear discrepancy like this?
 
The Wizzard said:
.......Why are they not part of a quickbuild wing?
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To answer your last question; the capacitive system is not offered as a quickbuild option because the two aluminum plates which are the heart of the system have to be built and wired into the fuel tanks during construction at additional cost of parts and labor. Once the fuel tanks are closed up, there is no way to retrofit those key parts.

4hy64h.jpg
 
The resistive float sensors can be removed and replaced. The capacitive sensor components are not accessible.
 
L.Adamson said:
I read about a high wing that crashed short of it's destination because the fuel cap on the top of the wing had been loosened when used as a hand hold. Being a new airplane, the two pilots didn't know which to trust, the fuel flow or fuel gauge. In this case, the gauge would have been the better option.

I certainly watch my gauges, but figure fuel used...totally based on the fuel flow meter. It's always within a quarter gallon or less for accuracy.

L.Adamson --- RV6A
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Good point. As Ronald Regan said, "Trust but verify". They should have landed and verified.

Mel said:
Maybe I'm missing something. Two Stewart Warner senders from Vans are $54. The Dynon converters are $100 and that doesn't count the fuel tank probes. To me it looks like the cost is more than double.
I have the resistance probes feeding the EI guage and find them to be very accurate.
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Mel, the senders are $50 each, $100 for the pair, just to be clear. The capacitive fuel sending units (which must be added when building the tanks) cost an additional $60. The restive sending units are $27 each, $54 a pair. So, the additional cost of adding capacitance fuel gauges is actually around $106. I can't believe I'm saying this but $106 is pocket change or two fill-ups for my pickup. :(

For those who are using the capacitance type sending units, take your time and encase the BNC connector in proseal before closing the tanks. These can leak and you want to make sure those connectors are completely covered.
 
9GT said:
I pondered this myself and had to make the decision when I was on the tanks. Having flown with capacitance probes before, it was an easy decision. I put the Princeton 5 point probes in my -10 tanks. http://www.aircraftspruce.com/catalog/inpages/princefuelprobes.php They were a lot of money compared to the Vans floats but I really like the accuracy of probes and they work well with an EFIS.
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Rats!

I wish that I would have known about this option about three months ago. I would have saved me a fair bit of time and effort.

Oh well! Now I have another 'lesson learned' for my next RV.

But thanks much for the tip '9GT'!

By the way, I have a bit of boring experience with float type gauges, and that is why I am using capacitance type gauges.
 
It seems the biggest problem with capacitance fuel senders is that they will read different values when the tanks are filled different fuels such as 100LL or MoGas. This is caused by the different relative static permittivity of the two fuels, or putting it another way changing the dielectric material that sits between the two plates.

Has anyone had experience of this?

I would like to be able to use either 100LL or MoGas or any other fuel that may become available in the future. It seems to me that the old fairly reliable method of using floats to sense the fuel level is the only way to go if this is a requirement. Does anybody have any different views?
 
islandmonkey said:
I would like to be able to use either 100LL or MoGas or any other fuel that may become available in the future. It seems to me that the old fairly reliable method of using floats to sense the fuel level is the only way to go if this is a requirement. Does anybody have any different views?
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I still think the best bet is to go with a fuel flow guage regardless of the type of fuel level gauge. These units are not all that expensive and can be retro-fitted without too much trouble. I just change fuel tanks every half hour when the GPS gives the signal. Knowing the actual flow, and what's left.......having the old float type guages doesn't bother me in the least.

http://www.aircraftspruce.com/catalog/inpages/flightdatafc10.php

L.Adamson --- RV6A
 
islandmonkey said:
It seems the biggest problem with capacitance fuel senders is that they will read different values when the tanks are filled different fuels such as 100LL or MoGas.....
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This is not much of a problem except that recalibration can be a tedius procedure. Nevertheless to assure accuracy, you must recalibrate the system when changing to a different type of fuel. Like any computer...garbage in garbage out.

L.Adamson said:
....... I just change fuel tanks every half hour when the GPS gives the signal......
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When to switch tanks....that brings to mind an unexpected and nice little function I came to appreciate with the IE capacitive system. The fuel gauge LED's start blinking...and my eye is naturally drawn towards that blinking when a fuel imbalance of 4 gallons occurs.

mwp6s7.jpg
 
islandmonkey said:
It seems the biggest problem with capacitance fuel senders is that they will read different values when the tanks are filled different fuels such as 100LL or MoGas. This is caused by the different relative static permittivity of the two fuels, or putting it another way changing the dielectric material that sits between the two plates.

Has anyone had experience of this?

I would like to be able to use either 100LL or MoGas or any other fuel that may become available in the future. It seems to me that the old fairly reliable method of using floats to sense the fuel level is the only way to go if this is a requirement. Does anybody have any different views?
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The problem with calibration of capacitance probes in different fuels is real. The dielectric constant of 100LL is in the neighborhood of 2. The dielectric constant of 100% ethanol is in the neighborhood of 24, so fuel containing even relatively small amounts of ethanol will throw an uncompensated capacitance fuel level system way out of whack.

There are dual-probe capacitance systems that are accurate across a range of dielectric constants. A second probe is installed so as to always be immersed in fuel to essentially measure the dielectric constant of the fuel and compensate the output of the measuring probe accordingly. I have seen some builders' logs that show installation of the compensation probe, so I A$$ume ;) that cost is not exhorbitant.
 
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-7 and been flying for 5 years with capacitive plates.


If I were to do it again I would put resistor floats in the tanks.

The calibrations were the same for car gas and 100LL until they started putting ethanol in the mogas.

It screws it up completely. It will read about twice what u actually have.

Other than that I haven't had any problems.

I have the EI guage connected to the vans cap sender.
 
I have the capacitive units.

I wouldn't bother if I were building again.

Less cost.
I just use them for a check, but rely on the FF to be more accurate.
I have had interference from my Archer comm antenna the effected the reading. The quantity would drop to zero if I transmitted to much. It would come back up after a minute without transmitting. I ended up removing the Archer and installing another belly antenna.

Kent
 
SW Senders do fail

I just had to replace my left sender around 270 hours. It was a relatively easy job and I will post the process in another thread. Messy, but did it in under two hours.
 
Need some clarification here please.

I've opted to put the capacitive senders in my fuel tanks (wings are being shipped next week!).

While doing my research on the different ways to build the tanks,the pitfalls some have encountered, what method "may" be the best way to go to prevent leaking, and the actual quality of components provided in the Van's capactive kit, here's what I'm doing.

Please let me know if I'm out to lunch or not.

- I have the self-sealing capsulated NAS1473A08 nut plates from Wicks to replace the regular nutplates. Looks like if there is going to be a leak, it will come through the threads.

- I have the Metric Viton? Fluoroelastomer O-Rings for the Stainless 8-32 1/2 inch socket head cap screws in the event fuel somehow gets by the capsulated nutpate.

- I'm replacing the nylon washers in the Van's kit with delrin. I've read that after about 5 years, the nylon may break down, which could create issues with the plates.

- I'm using 2 Male BNC connectors, Part # 31-236 RFX AMPHENOL, due to the possible leakage from other brands?

- 24 gauge teflon wire as other wires will deteriorate in fuel?

For anyone that has been using the standards Van's capacitive kits for 5 years, have you had any issues? Has anyone had experience with wires deteriorating in fuel tanks?

Any info would be great!

Cheers,

Don
 
Vans gauges......... switched tanks at the 2.5 mark on the gauge. Landed and filled the tank to the top with 16.3 gallons in a 19 gallon tank. 2/10ths is close enough for me.
 
Don Patrick said:
For anyone that has been using the standards Van's capacitive kits for 5 years, have you had any issues? Has anyone had experience with wires deteriorating in fuel tanks?
Any info would be great!
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Six years +, zero problems with capacitive senders.
 
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