Capacitive Fuel Sender Calibration - RV-7A

[rzbill]

I built my tanks and installed the Dynon frequency to voltage units because they were a tiny elegant package. They work. However, the meager 180 picofarad change from empty to full is not anywhere close to linear because of tank geometry. Dihedral plus le radius plus partial overlap of capacitance plates.

The graph of voltage vs fuel content has a kink in the middle that must be programmed out via curve matching software in the display. GRT instruments do this. Others probably too but I have no direct knowledge.

Also the GRT feature of showing total measured fuel from tank gages on top of the fuel flow subtractive totalizer is really nice. Gives confirmation that the tanks are reading correctly.

[KatanaPilot]

Originally Posted by BillL

Every thing on my plane works pretty well. If it is there it works, except the fuel gauges. I rationalize that they are absolutely accurate below 7 gallons. The left works from 9 down and the right maybe 14 and down. Above that they can not be trusted. I know it and live with the exception as a totalizer is pretty accurate and I have a dip gauge that is accurate within 1/2 gal, and consistent with the totalizer. So I know what I start with and the gauge(s) is/are good for the end of flight. Usable but not acceptable.

Is there a Kit Planes article? Vans RVAtor report? Vendor report?

CiES sensors - a master inboard and slave outboard in the tank will work empty to full. Quite expensive.

RV-14 builder info here - https://vansairforce.net/community/s...d.php?t=184811

There are about to be a number of RV-10ER tanks built with these. I assume they would also work in a 7, but might not be suitable as a retrofit - since you have to install mounting hardware some where in the outboard most bay. The ER tanks have them mounted on the aft baffle.

[pazmanyflyer]

Originally Posted by BrianMatice

I will definitely look into the Princeton adapters. Does anyone have a source for these?

The Princeton Electronics probe ownership (https://www.princeton-electronics.com/) has been sold/transferred and they are now sold and supported by Red Avionics at https://www.redavionics.com/

[Ralph Inkster]

Questions for Brian-

You mention second hand wings.. were they previously flown (& presumably the capacitance tank senders previously worked properly)?
Are these new Dynon adapters?
In your calibration attempts, was this the results for the first tank, or did both tanks register the same way?
Did you swap the adapters between tanks to see if results would vary?

Before you decide to change out to float senders or shell out big bucks for some other brand capacitance adapters, I think it would be wise to test the Dynon adapters you have & exhaust the potential for some internal tank wiring issue first. Unfortunately to be thorough doing this would mean removing the tank(s), opening the access panel(s) & testing connectivity between the inboard plate & the center B&C connector pin (I still suspect that the adapter & wiring is not getting good connection to the inboard plate, if so, easily fixed)

You would have to remove the tanks to retrofit & properly adjust float senders anyway.

Good luck

[BillL]

Originally Posted by KatanaPilot

CiES sensors - a master inboard and slave outboard in the tank will work empty to full. Quite expensive.

Thanks Krea, at least I would have accuracy for 14-16 gal each side. Yes $$$, it must be a resolver as the core device. At least it is an alternative.

[Walt]

I've had the Van's capacitive senders in since the beginning with the EI FL-2C, which they used to sell a converter for, which apparently in no longer available.
I've since upgrade the FL2 to the MVP50 and then to my current CGR30-P. The calibration on the CGR30 was a little squirrely and I ended up just using the same cal numbers from the MVP50. Anyway, it's always worked pretty good from full to empty but not great. This thread has me wondering if the 'RED' (Princeton) sensors would improve things but not sure if I want to spend $400 on that gamble.

[BrianMatice]

Originally Posted by Ralph Inkster

Questions for Brian-

You mention second hand wings.. were they previously flown (& presumably the capacitance tank senders previously worked properly)?
Are these new Dynon adapters?
In your calibration attempts, was this the results for the first tank, or did both tanks register the same way?
Did you swap the adapters between tanks to see if results would vary?

Before you decide to change out to float senders or shell out big bucks for some other brand capacitance adapters, I think it would be wise to test the Dynon adapters you have & exhaust the potential for some internal tank wiring issue first. Unfortunately to be thorough doing this would mean removing the tank(s), opening the access panel(s) & testing connectivity between the inboard plate & the center B&C connector pin (I still suspect that the adapter & wiring is not getting good connection to the inboard plate, if so, easily fixed)

You would have to remove the tanks to retrofit & properly adjust float senders anyway.

Good luck

2nd hand wings have never flown. Using new Dynon adapters. First three points all measure the same voltage (0, 2, 4 gal). Both tanks do the same. If there is a wiring problem, the mistake was made in both tanks.

[BrianMatice]

Originally Posted by Desert Rat

I think I see a basic misunderstanding here.

You're not measuring the delta between the two plates. Each plate measures the delta between the plate and the rib it's mounted on. The reason there's one in each end of the tank is specifically because of the dihedral.

FYI I have the same situation with used wings from 2007. I'm not at that point yet so I'm very interested in how this works out for you.

I was under the assumption that we were reading the capacitance between the two plates. But now that you mention this, the ground is the tank itself, the plate is the center conductor. I think this implies that the connection is broken to the inboard plate because it does absolutely nothing. I'm not sure how I'm going to get to that wire to check it out. They both do the same, so I can only assume it was an error in construction.

[bhester]

I put the capacitive plates in mine back in 2005 and they worked great with the Princeton converters. I had to build new tanks last year due to 2 deer denting mine. I put the original design plates in the new tanks and they work very good also. Here is my build picture from last year disregard the 2010 dates noted that should be 2021, got to change that.
http://www.newtech.com/bobbyhester/2021Flying.htm

The old Princeton converters are now the Red Converters:
https://www.redavionics.com/product/...=false&q=false

My good buddy Doug Rohrer from Bowling Green, KY made me the spacers that are need for installing the plates. Oh by the way he has an artical in this months (Sept 2022) EAA magazine about his building experiences.

[RV7A Flyer]

Originally Posted by BrianMatice

2nd hand wings have never flown. Using new Dynon adapters. First three points all measure the same voltage (0, 2, 4 gal). Both tanks do the same. If there is a wiring problem, the mistake was made in both tanks.

This is what I and others have been trying to tell you...they Dynon adapters use a very tiny portion of the available range, and it doesn't show up as any difference at all during calibration (although, if you look at the actual data file, it's there, just waaaaay down in the smaller significant digits). I had the exact same thing happen...it was looking like the values were changing at all. They were, but the resulting calibration curve kinda sucked. Tried it at least twice before ditching the Dynons and going to Princetons.

The Princeton converters get set up to know what full and empty readings are, then they use *those* values as 0 and 5V, *then* you start over at empty and do the 2-gallons-at-a-time thing. It's time-consuming but much more accurate.

Others claim good results with Dynon's converters, but I'd recommend the Princetons. Your call.