Fuel sending units

[OLDSAM]

I am fixin' (a southern term meaning preparing) to order the wings for my 7A, and need to know the pros and cons of the capacitive fuel sending units vs. the float sending units. From their brief description, it appears that I would be on my own for an instrument to accept and display the results from the capacitive sending units, thus an increase in the hassle factor. The question thus becomes: Is there an advantage to the capacitive sending units that would justify said increase in hassle factor? I assume there is a reduction in the number of moving parts, anything else?

Oldsam
RV7A, tail nearly done, fixin' to order wings.

 

[Ironflight]

I can't compare the two, since I have only used the float gauges, but I ave found them to be adequate for the purpose. To be honest, I rarely rely on any type of gauge - I use the fuel flow and totalizer in my avionics (plus my wrist watch and common sense) to figure out how much fuel is remaining. Float gauges in an RV are not going to tell you anything about the top few gallons of fuel, because of dihedral.

Paul

 

[Birkelbach]

I can't really compare the two either but I have the capacative gauges. There is little hassle factor in finding something to read them because there are converters that you can buy that make them compatible with just about any instrument. I have the EI Guage which was pretty expensive but I LOVE it.

It is very accurate. When the thing says 5 gal left in a tank, it'll take 16 gal out of the truck to fill it up. I still tend not to trust it (training and all) and, like Paul, use my totalizer, watch and that egg shaped thing that God put on top of my shoulders to figure out how far I can go. It is nice to have an accurate fuel indication though.

Another benefit is that it will read those "dihedral" gallons that the floats can't get to. A pretty major drawback is that it will only be accurate for the fuel that you calibrate it with. If I were to switch to auto fuel it'll read different from what it would read with 100LL. I haven't tested this yet, so I don't know the magnitude, but it is an issue.

It doesn't have any moving parts to break, but on the flip side of that you can't get the plates out without taking the tank apart either. If mine ever do fail, I'll be putting in some floats .

I also put a flop tube on one tank and the capacative plates don't have to be modified for that installation. Minor issue, but you asked.

 

[Noel Simmons]

I have used both

I have used EI capacitance tubes that ran from the lower corner to the upper corner of the fuel tank to try to read every drop, I had an RV-7 with two main tanks and two aux tanks for a total of 70 gallons. This was going to a Grand Rapids Tech Horizon 1, GRT needed converters to read the EI probes (($200+$65)*4). results were the GRT reads the 0-5 volts from the converter and displays that as 21 gallons, the aux tanks being 14 gallons also got displayed as 21gallons but toward the bottom of the tank the error was smaller and smaller until 0 was indeed 0. As the fuel was transfered to the main tanks the mains would go up exactly 14 gallons.
IMHO this was a pain as the fuel totalizator was still way more accurate

Used the Van's capacitive fuel level and float type with a Blue Mountain EFIS 1. The set up of the EFIS allowed this. Well to be nice, I am glad the totalizator mostly worked

Used Van's floats on several of my airplanes now. These are my favorite, as they are spot on when they are indicating, indeed you lose the top of the tank due to dihedral. It doesn't mater if you are hooking them to an EFIS or the Van's gauges they are right. Also there is no dampening so you can slosh the fuel in the tanks to check that indeed they are working

Hope this helps,

Today I am putting $4000.00 of tires on a cub good thing they sent me a bag of peanuts to comfort me

 

[OLDSAM]

Thanks, guys,
Sounds like a case of if it ain't broke, etc. Think I will stay with the basic float system, something my feeble old mind can comprehend. Like you all, for my purposes the gauges are just something for the passenger to look at and derive comfort from, or maybe tip me off to a leak. The power settings and the watch are what tell the tale, never flew with a totalizer before, looking forward to it.

Just think how many Piper Cubs you used to be able to buy for what those tires cost now!

OldSam