Horizon WS "Too Much Fuel"

Still working out a few glitches in my somewhat-new-to-me RV-9A with a GRT Horizon WS and an EIS 4000.

I like these gadgets, but the learning curve is a bit steep.

The previous owner didn't quite nail the calibration of the fuel tank senders. I understand from research here that it can be a bit of a bear to get that right. I can actually live with what I have (the fuel FLOW is spot on, and that's all I really need), BUT the right tank, when full, gives me an annoying alarm that it is TOO full. It reads about 19.5 when it has 18 gallons, and it sets off my flashing red light associated with my EIS 4000.

My fuel info seems to go from my EIS 4000 to my Horizon WS. For example, I set full tanks using the EIS 4000. But in any event, I can't figure out how to turn off this alarm in either box. I tried increasing the max fuel number on the WS without effect.

Documentation seems a bit unclear on this issue. Any ideas?

Thanks!
DMG

I’ll take a stab at this. The actual calibration procedure is on the very last page of the EIS manual (download from GRT).
I’m a bit surprised the issue is on one tank. Usually left and right calibrations are very similar.
1. Look for any documentation from the builder that might show which AUX input he used for the right tank. If none, step thru all the labels, see if you can find which aux (AUX1, AUX2, etc.,) is assigned to the right fuel tank. That should work, but if it doesn’t you’ll have to trace the wire.
For this example let’s say the right tank gauge is on AUX2.
2. Go to the page where scale factors (SF) and offsets (OFF) are entered.
With the right tank full, reduce the AUX2SF entry by about 10%, exit out of setup. What does the right tank read? If it’s not less than the 18 gal max, go back and lower AUX2SF some more. Since the float will hit the top of the tank before it is really full, you want this number to be a few gal less than max capacity.
At some point in time you should do the entire calibration procedure. The EIS calibration is just empty and full (or float at top of tank) but the EFIS readout can be calibrated at muliple fuel levels, making it very accurate.

The flashing red light shows EIS alarms. For EFIS generated alarms, the entire fuel gauge bar graph will blink red. I find it convenient to set the EFIS alarms a bit more conservatively than the EIS alarms. e.g., CHT alarm on EFIS at 420; on EIS at 430. So if EFIS CHT starts blinking red, I need to think about what’s going on. If the big red light comes on (EIS alarm) I need to take action, now!

Fuel calibration - it?s not easy

A gentleman at Vans support once told me that a ?full? tank reading usually occurs when the indicator shows about 16 gallons due to the nature of resistance type fuel senders and how they fit in the tank. I believe the FAA only requires the gage reading to be accurate when the tank is empty since that is when it?s most important for the fuel tank reading to be accurate.

Read the GRT instructions carefully before you start the calibration process. Here is the web page for those instructions:
http://grtavionics.com/media/Resistive-Float-Fuel-Senders-EIS.pdf

You will also want to reference the GRT Fuel Scale and Offset calculator
http://grtavionics.com/home/eis-eng...uel-probe-scale-factor-and-offset-calculator/

The calibration process is really a two person job. One person to monitor the EIS screen to identify when it stops moving and a second person to actually drain and then refill the tank in one gallon intervals. Have available four clean 5 gallon gas cans to hold the fuel you drain out and then refill into the tanks (again one gallon at a time).

When it?s all said an done after you?ve identified when the EIS stops moving during the drain and refill process and you?ve calculated your new AUXSF AND OFFSET FACTORS, your gages should be reasonably accurate between 16 and 1 gallons. I personally use the EIS fuel flow information for accurate ?fuel on board? information and the ?gage reading ? for five gallon tank balancing information. I also have my EFIS set up to remind me every 30 minutes it?s time to switch tanks.

Good luck.

It is not clear to me whether the OP wants the calibration fixed or the warning removed.

Since no one has talked about the warning, here it is.

The EIS has its own set of warning limits accessed by the "set pages" command that is described on page 8 of the EIS manual. If you plan to use the EFIS for warning limit controls, then the EIS limits should probably be set to zero which turns off the EIS warning for that particular measurement. The EIS limits ARE NOT controlled by the EFIS. They are totally separate. Both EFIS and EIS limits can be used but that is an owner choice.

I imagine that the previous owner either has accidentally typed in a limit or it is a wrong limit for the right tank, causing the warning.

As already mentioned, the float gages can't physically measure full tank volume. A VAF search could probably get you an RV6 tank volume to target when tanks are full..

BobTurner said:

2. Go to the page where scale factors (SF) and offsets (OFF) are entered.
With the right tank full, reduce the AUX2SF entry by about 10%, exit out of setup. What does the right tank read? If it?s not less than the 18 gal max, go back and lower AUX2SF some more. Since the float will hit the top of the tank before it is really full, you want this number to be a few gal less than max capacity.

Click to expand...

This solved my problem perfectly. With the tank completely full, I reduced the AUX2SF entry until the right tank read 18.

AUX2 is in fact my right tank; AUX3 appears to be my left, and AUX1 appears to be fuel flow.

It makes sense to me that after a proper calibration the right tank should read LESS than 18 when full, but for now I just wanted to stop the overfill alarm. I also want to see just how off the calibration actually is with this new scale factor.

For what it's worth, I appear to have capacitive fuel sensors, with Princeton Electronics converting that to analog. It also appears that my two tanks have rather different SF and OFF settings.

I'm saving the calibration procedure for warmer weather and the opportunity to enlist a friend to help. While I ponder that, and while I've got the eyes of actual builders: are there idiot-proof safeguards for defueling aircraft? I'm paranoid about that sort of thing after somebody sent me a youtube video of gas pump conflagrations.

Many thanks to everyone for the info. I really appreciate it.

By any chance are you running mogas in one tank?

Mike S said:

By any chance are you running mogas in one tank?

Click to expand...

I was just pondering the same thing!! No, but maybe the original builder was?!?

Well, if so that would explain the "why" of your problem. Or, former problem

At least you have the issue resolved now-------Bob is really good with the GRT stuff.

BobTurner said:

The EIS calibration is just empty and full (or float at top of tank) but the EFIS readout can be calibrated at muliple fuel levels, making it very accurate

Click to expand...

Bob,
The nice thing about VAF is someone always points out something not known to to me. I am familiar with setting upper and lower fuel tank limits on my Horizon WS EFIS and having it display approximate fuel in my left and right tanks on the engine page but how do you ?calibrate? multiple fuel levels for each tank on the WS? I?ve looked in the manual for this but I either have missed this information or don?t understand what I?ve read. Please illuminate.

Download the GRT HX setup manual.
Pages 5-5 and 5-6 are basic empty-full set up info.
Page 6-7 tells you how to bring up a calibration table (drain tank, note reading, put 0 in the column for actual fuel; add 2 gal of gas, note reading and actual(2); add another 2 gal, note reading and actual (4) fuel; etc.).

Edit: I should say that I’m assuming the WS works the same as the Hx or HS that I’m familiar with.

BobTurner said:

Download the GRT HX setup manual.
Pages 5-5 and 5-6 are basic empty-full set up info.
Page 6-7 tells you how to bring up a calibration table (drain tank, note reading, put 0 in the column for actual fuel; add 2 gal of gas, note reading and actual(2); add another 2 gal, note reading and actual (4) fuel; etc.).

Edit: I should say that I?m assuming the WS works the same as the Hx or HS that I?m familiar with.

Click to expand...

Thanks. I?ll check this out with GRT.