Moeller Float Gage Accuracy

[NinerBikes]

Bob, this is something we need to verify in your 2015 RV-12. Very valuable thread, thanks to all that have contributed.

[AirHound]

Originally Posted by Piper J3

I have four ways to determine fuel quantity before flight: Moeller, sight-gage on side of tank, Dynon D-180, and dip stick.

The only one I completely trust is the dip stick ? very accurate / never lies?

Jim,
Did you make your dip stick? If so, any specs you can share?

Thanks and Happy New Year!
Doug

[AirHound]

Originally Posted by rvbuilder2002

This is not a problem with the RV-12 (and not exclusive to the RV-12 either... all of the other RV models have gauges that can't read the upper 4 gallons or so because of wing dihedral). When is it that important to have a absolute gauge indication of the first 3 or 4 gallons that get used. The important thing is for accuracy at that last 3 or 4 gallons. The RV-12 tank does well with this.

A long / full span skinny tank in the wing with the dihedral tilt will be effected even worse than any of the other RV's are.

Scott,
I didn?t build my 2012 RV-12. Was wondering if the occasional strong fuel pump gas stream can neg impact fuel tank floats/innards/accuracy?

Thanks and Happy Flying New Year!
Doug

[rvbuilder2002]

Originally Posted by AirHound

Scott,
I didn?t build my 2012 RV-12. Was wondering if the occasional strong fuel pump gas stream can neg impact fuel tank floats/innards/accuracy?

Thanks and Happy Flying New Year!
Doug

I don't know if I understand your question correctly, but if you mean a high velocity stream from a fuel nozzle having a neg. effect on the fuel tank and sender? No, I am not aware of any problem caused by that. I don't see how it would be possible since the filler tube makes the fuel enter the tank pretty much straight down at the back of the tank but both of the fuel level floats are well fwd in the tank.
A change in fuel gauge accuracy is usually caused by an increase in resistance between airframe ground and the mounting flange (ground path) of the fuel level sender.
The RV-12iS redesign included adding a ground wire between the airframe and one of the sender mounting screws, to help mitigate this problem.

[Piper J3]

Originally Posted by AirHound

Jim,
Did you make your dip stick? If so, any specs you can share?

The stick is wood approx 1/8" x 3/8" x 36". The end that gets inserted into the tank is pointed so it can sneak around the fuel return tube at the base of the filler neck. Start with empty tank and fill with 2 gallon increments each time inserting the stick and marking the level with a graphite pencil. Dead nuts...

[RFSchaller]

I did what Jim did and used flexible translucent tubing. Although the shape of the tank isn?t a uniform cube I found that once you?re past the sloped tank floor it was pretty much one gallon to the inch. I got 20 gal into my tank, but that filled most of the filler neck so as soon as the fuel started filling the neck the linearity shifted. I?ll check my dimensions on the marks when I?m at the hangar on Wednesday and post them.

[VHRV12]

Originally Posted by rvbuilder2002

I don't know if I understand your question correctly, but if you mean a high velocity stream from a fuel nozzle having a neg. effect on the fuel tank and sender? No, I am not aware of any problem caused by that. I don't see how it would be possible since the filler tube makes the fuel enter the tank pretty much straight down at the back of the tank but both of the fuel level floats are well fwd in the tank.
A change in fuel gauge accuracy is usually caused by an increase in resistance between airframe ground and the mounting flange (ground path) of the fuel level sender.
The RV-12iS redesign included adding a ground wire between the airframe and one of the sender mounting screws, to help mitigate this problem.

Hmmm that,s interesting Scott, I have just calibrated the fuel tank sender in my 12 with Skyview and a standard 19.8 US Gal tank and had trouble getting good figures with nice voltage "steps". Next time I turned the power on the fuel quantity was blank. Turn out to be a poorly grounded sender. Made a 12" jumper with a couple of ring lugs, grounded to sender mounting screw with an MS35338-38 star washer and plenty of goop and the other end to the conduit P Clamp on the spar carry thru... Perfect!

[NinerBikes]

Some observations here in Southern California, where we fly the RV-12 year round.

Moeller doesn't start registering off of full until 4 to 5 gallons are burned off. That leaved the Moeller having a range of your last 15 or 16 gallons. Last 2 fillups, the Moeller was showing smack dab a half a tank left. Fillups were 12.2 and 11.7 gallons, brimmed to maybe 2 inches short of the top of the fillup neck. So ABOUT 8 gallons left, when the Moeller shows half a tank.

The prop on this plane is tuned not for climbing but for cruising. At 1300 # with both of us 5000 ASL, throttle to the wall, we see 5250 to 5300 rpm, level flight, max. LL100, will burn just over 5 gallons an hour at 112 kt IAS. For some reason, Mogas seems to give another 60 to 80 more rpms at full throttle? Just observations.

Any ideas why more rpm on the Mogas, greatly appreciated. Perhaps the Rotax, being designed for Mogas and the lower octane, makes more torque due to the burn characteristics of the flame front of Mogas?

Just a FYI.... as always YMMV, trust, but verify, this is but one data point of many.

[pilotyoung]

Jim,

Is there any reason a dowel rod could not be used to measure and mark the fuel quantity in the tank?

[rvbuilder2002]

Originally Posted by NinerBikes

The prop on this plane is tuned not for climbing but for cruising. At 1300 # with both of us 5000 ASL, throttle to the wall, we see 5250 to 5300 rpm, level flight, max. LL100, will burn just over 5 gallons an hour at 112 kt IAS. For some reason, Mogas seems to give another 60 to 80 more rpms at full throttle? Just observations.

Any ideas why more rpm on the Mogas, greatly appreciated. Perhaps the Rotax, being designed for Mogas and the lower octane, makes more torque due to the burn characteristics of the flame front of Mogas?

Your prop isn't pitched for cruising.... it is over pitched.
This will have a negative effect on oil temp in hot weather and can cause other problems (besides giving up climb performance that you don't have to).

I have no comment on the RPM difference. I have never seen any indication of a change with fuel type. My guess is that you are seeing differences with different weather conditions (density altitude).