Fuel tank calibration

[dakdriver]

Fuel tank calibration



I have the HDX1100 installed in my RV6.

I have attempted to calibrate my fuel levels several times. All have failed. It would appear that my sender units (The rheostat type) are too old and not sending the correct readings.. These worked albeit not accurately on the previous gauges (UMA 1 inch) but were good enough to show when a tank was close to empty. These have been removed with the installation of the HDX1100.

A recent incident occurred when operating recently, I missed a fuel tank change and when I figured I had missed it I changed tanks. This occurred when joining the circuit.
After landing I refuelled and put 69 litres into the tank.

I would like to install capacitance senders to get the system read the fuel levels with some accuracy



Can anybody recommend the best type and where I can obtain them

Thanks

Bruce

 

[jakej]

Do you have a fuel flow unit installed? IMO a ’calibrated’ Fuel Flow computer is the best insurance against notoriously inaccurate fuel gauges.
’we’, in Oz are required to have fuel gauges however a lot of pilots don’t trust them & rely on the Fuel Flow computer. YMMV
ps - with a fuel computer your Dynon also has the ability to remind you visually & aurally to warn to change tanks.
Red Avionics have a reasonably priced capacitance fuel level unit.

 

[PaulSS]

I think you'd be wasting your time and money. The brand new RV8 I was involved with had capacitance sensors and we couldn't get those calibrated to any great accuracy. They were replaced with resistive floats and those were no good either. I don't know if it's the tank shape & dihedral but you are not going to get great readings in an RV, in my view. Okay for mid range but not much good at the top and bottom of the tank.

As Jake said, of more use is the fuel flow versus original contents. Funny enough, the RV8 was in Oz

 

[dakdriver]

Thanks for the information. Jake and Paul

The rheostat senders worked the UMA gauges loosely…Like they never showed a full tank but were reasonable at half tank and as the fuel went down so did the gauge but when it showed pretty close to empty I had over 10 liters available.
I flew for nearly 10 years like this with no issues. As they indicated roughly what was in each tank. These were removed to fit the HDX100 I now have no reliable indications on each tank. (I This caught me out just recently when I forgot a tank change and I don’t want to go there again).

So maybe I should reinstall the uma gauges and just use the Dynon tantalizer for my total fuel on board

I couldn’t calibrate the fuel gauges so the tank indicators on the screen have no quantity needles


Ok so I could also use the Dynon to warn me when to do a tank change. I have not found that function yet but will defiantly look into it,

I have the red cube fuel flow computer

 

[Carl_Froehlich]

Some thoughts:
- Fuel flow senders are very accurate using the SkyView EMS - until they are not. The senders assume the tanks start off with a know amount of fuel (typically you reset after fill up) and they assume all the fuel coming out of the tank goes to the engine. If you have a leaking sump valve or other fuel leak you will be in for a surprise.
- Properly installed RV float senders locations translate to them never reading more than 3/4 full. The wing dihedral dictates this. However as you burn fuel they become amazingly accurate if you took the time to calibrate the SkyView EMS correctly. So the value of the float senders becomes evident as a cross check for fuel against the fuel flow measurement once they come into the indication range.

One time, and one time only I let a line guy fill my RV-8 tanks. I found out later on the cross country that he shorted me ~7 gallons from full. The float senders gave me this warning.

Capacitive senders have a history of never really working or premature death. I don’t recommend them in an RV.

Carl

 

[swatson999]

Capacitive senders have a history of never really working or premature death. I don’t recommend them in an RV.

Carl

I put the stock (at the time) capacitive sensors in the tanks on my RV-7A, and it's been flying for 12 years now with not a single issue. They're accurate to a few tenths of a gallon when properly calibrated. N.B., I did have issues with the stock Dynon C2V converters, but switched to the 2-point Princeton converters, and they'd been spot on.

I have 2 friends with -8s and one with a -7, similar setups (different avionics), and zero issues.

 

[RV8JD]

Capacitive senders have a history of never really working or premature death. I don’t recommend them in an RV.

Carl

My previous RV-8 has the Vision Microsystems capacitance fuel level sensors. My buddy has that RV-8 now and the fuel levels are still dead accurate from full tanks to empty, and the airplane has about 2400 hours on it. Never had a problem with the system. I miss those fuel gages!

My current RV-8 has the standard float sensors at the inboard tank end and I don't like them. Yea, they kinda work from about 14 gallons down, but I'm spoiled after flying my previous RV-8 for 1900 hours with the excellent VM capacitance system! Luckily, the fuel flow computer/totalizer is pretty accurate, but the float gage readings not so much.

 

[dakdriver]

Some thoughts:
- Fuel flow senders are very accurate using the SkyView EMS - until they are not. The senders assume the tanks start off with a know amount of fuel (typically you reset after fill up) and they assume all the fuel coming out of the tank goes to the engine. If you have a leaking sump valve or other fuel leak you will be in for a surprise.
- Properly installed RV float senders locations translate to them never reading more than 3/4 full. The wing dihedral dictates this. However as you burn fuel they become amazingly accurate if you took the time to calibrate the SkyView EMS correctly. So the value of the float senders becomes evident as a cross check for fuel against the fuel flow measurement once they come into the indication range.

One time, and one time only I let a line guy fill my RV-8 tanks. I found out later on the cross country that he shorted me ~7 gallons from full. The float senders gave me this warning.

Capacitive senders have a history of never really working or premature death. I don’t recommend them in an RV.

Carl

Hi Carl Thanks for your comments.
When i installed the HD1100 I calibrated both tanks several times with these issues (cannot remember the exact readins but the went like this)

Starting empty ohms reading 3ohms put in 5 ltrs ohms read 5ohms then added another 5 litres ohms read 7ohms then another 5 liters ohms read 5 liters then it asked me did I put 5 liters in said yes carried on with the next 5 liters and so on the ohms readings went up and down during the fill

This is why I suspected the sender units were worn out or at least not reading accurately enough to register the amount going in.
Ok so maybe the old senders I have need replacing with the same as I have It will be a cheaper fix anyway


Thanks for your comments

Regards

Bruce

 

[jakej]

Bruce - I usually give the wing a thump above the sensor (Float types) after adding fuel at each step of the fill - it does help to mitigate the hysteresis inherent with the float type units.

 

[Carl_Froehlich]

Or, the sender arms a hung up on something. With a few gallons in each tank rock the wings as best you can. This fixed an new RV-8 so perhaps it will help you.

Carl

 

[dakdriver]

Bruce - I usually give the wing a thump above the sensor (Float types) after adding fuel at each step of the fill - it does help to mitigate the hysteresis inherent with the float type units.

Hi Jake
Today I removed the sender unit and did a test with an OHM meter It seemed to be working fine a bit shaky in a couple of places but on whole it seemed to be working. This figures as they were hooked up to the UMA gauges and worked fine. So from you and Carl’s suggestion I will attempt another calibration and after each 5 liters I will thump the tank and rock the wings and see if this makes any difference



Thanks for your help



Regards

Bruce

 

[soarhead]

In my experience, in any GA aircraft I have flown, the fuel gauges are very accurate in two positions. Full and empty. Everything in between is total fiction. The best fuel gauge is a fuel flow sensor backed up by a watch and regular fuel checks over waypoints on a fuel log, just to verify no leaks.

 

[Marc_J._Zeitlin]

In my experience, in any GA aircraft I have flown, the fuel gauges are very accurate in two positions. Full and empty. Everything in between is total fiction. The best fuel gauge is a fuel flow sensor backed up by a watch and regular fuel checks over waypoints on a fuel log, just to verify no leaks.

Well, all I can say is that the capacitance fuel level senders (from Princeton and now Red Avionics) have been calibrated and read within 0.5 gallons of the actual amount in the tank at ALL levels, in BOTH tanks. So, while TC'd aircraft might have really crappy fuel level senders (and I've never known them to be anywhere near as crappy as you're making them out to be), it's most certainly possible to have accurate fuel level indications at all levels. And I've checked the levels with the calibrated fuel flow gauge/totalizer, which is also accurate to within 2% of tank capacity (about 1 gallon out of 58).

 

[dakdriver]

Well, all I can say is that the capacitance fuel level senders (from Princeton and now Red Avionics) have been calibrated and read within 0.5 gallons of the actual amount in the tank at ALL levels, in BOTH tanks. So, while TC'd aircraft might have really crappy fuel level senders (and I've never known them to be anywhere near as crappy as you're making them out to be), it's most certainly possible to have accurate fuel level indications at all levels. And I've checked the levels with the calibrated fuel flow gauge/totalizer, which is also accurate to within 2% of tank capacity (about 1 gallon out of 58).

Hi Marc

Thanks for the information. I have ordered two new senders from Vans after several attempts at recalibration I removed one of my senders and set it up on the bench. The results were not good there were several positions where the readings stayed the same and several readings where I had zero readings. I guess these things don’t last forever, they sort of worked with my UMA gauges not accurately but enough to know approximately where the fuel level was. As I now have the Dynon system installed and most of the functionality operating this was one of the issues I had not got to until now.

So as soon as I have the new senders I will install them and try again to recalibrate.

 

[greentips]

I had the original SW gauges in my C182. I replaced them with resistive gauges from MacFarlane. The old gauges had resistive gaps and non-linear responses on the bench. One failed with a Full indication at empty. These had been in the airplane for 55 years and did OK with the factory gauges. The new gauges on the bench were much more linear and consistent with each other.

When I calibrated the new senders with the Dynon, I went through the calibration process the first time using a volume method which was slow and cumbersome. I calibrated the second tank and the aux tanks by weight using a postal scale, filling the container to a precise fuel weight, then converting to volume. This gave much better results and faster than filling a container to a fill line and pouring. I went back to the first tank and re-did the calibration. Things seem to be working reasonably well, but flight timers and fuel flows are what I depend on. I did notice the aux tanks (Flint) gauges are sticky, even after being in the airplane for several years. When I installed the tanks, I put an inspection port over the fuel gauge positions to permit the gauges to be serviced without removing the tank from the wing.

Within the constrains of the airframe and tank designs, (bladder tanks, long and flat), the gauges are ok in straight and level flight.

 

[swatson999]

Hi Marc

Thanks for the information. I have ordered two new senders from Vans after several attempts at recalibration I removed one of my senders and set it up on the bench. The results were not good there were several positions where the readings stayed the same and several readings where I had zero readings. I guess these things don’t last forever, they sort of worked with my UMA gauges not accurately but enough to know approximately where the fuel level was. As I now have the Dynon system installed and most of the functionality operating this was one of the issues I had not got to until now.

So as soon as I have the new senders I will install them and try again to recalibrate.

The info you quote is about the *capacitive* style sensors, and I think you're talking about the float type sensors. Two totally different things.

FWIW, my capacitive system with the two-point Princeton converters (just like Marc) have been dead nuts on for 1000 hours now.

 

[dakdriver]

Thanks for all the advice.

My senders arrived, tanks removed. old sender units removed. new sender unit installed. each tank recalibrated once only and the both worked perfectly.
I should have known better that when upgrading a modern system into a 16 year old aircraft some things are bound to be unusable.
I tested the old senders after romoval and found readings were all over the place when they actually read anything.
So am pleased to report my fuel gauge for each tank is reading very accurately.
I am absolutely thrilled with flying with the Dynon HDX1100. It has rekindled my enthusiasm for flying once again.

Thanks again to all those who advised me on this issue

Regards to all