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Useful Complements to Moeller Gauge

WingedFrog

Well Known Member
After closing my fuel tank windows due to leaks (at Hobbs 170 /3 years flying) I missed the precision of the content they were offering. Indeed the Moeller gauge is too inacurate and not linear from empty to full. Worse, in case of failure of the Moeller as we have already seen happening, you have no way to know where you stand above the max of the in-tank sensor.

Like the Fuel Tank Windows, this rod made of 1/8 inch fiberglass will not lie. It slides easily in the fuel tank neck passed the return fuel line. Just calibrate it from an empty tank and print the calibration on a piece of measuring tape as seen on the picture:

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Keep this picture of the Moeller gauge dial with a Gallon scale with your Checklist:

view
 
Thanks Jean-Pierre, that is helpful for me. I am just getting ready to calibrate my tank for the first time. I can certainly see the benefit to having a visual reference in addition to the Moeller gauge for those of us without the sight window. By the way, did you ever say hello to Robert Fini for me? (sorry, that should probably be in a PM). Paul
 
Not in an RV-12, but I just use a dowel with notches in it. Every few years I renumber the notches with a pencil.

The only important detail is that the stick needs to be long enough that it can't possibly fall into the tank.

Dave
 
After closing my fuel tank windows due to leaks (at Hobbs 170 /3 years flying) I missed the precision of the content they were offering. Indeed the Moeller gauge is too inacurate and not linear from empty to full. Worse, in case of failure of the Moeller as we have already seen happening, you have no way to know where you stand above the max of the in-tank sensor.

Like the Fuel Tank Windows, this rod made of 1/8 inch fiberglass will not lie. It slides easily in the fuel tank neck passed the return fuel line. Just calibrate it from an empty tank and print the calibration on a piece of measuring tape as seen on the picture:

Great idea, and although I could not locate a 1/8" fiberglass rod, I did try other materials. The problem that I had was in getting a consistent reading due to the large filler tube allowing the bottom of the rod to drift to different locations on the bottom of the tank. How do you control that issue? Also, a source for your rod would help. Thanks in advance...........Tom
 
Jean-Pierre

Looking at your photo of the Moeller gauge with the gallon markings added gave me an idea to take it one step further.

I'm going to see if the local vinyl print shop can't print up a transfer so the gallon numbers can be affixed to the face of the gauge ... either as individual numbers all transferred at the same time to keep the spacing and alignment proper or as a single round piece of clear vinyl that will cover the entire gauge face with the numbers printed onto the vinyl.
 
Great idea, and although I could not locate a 1/8" fiberglass rod, I did try other materials. The problem that I had was in getting a consistent reading due to the large filler tube allowing the bottom of the rod to drift to different locations on the bottom of the tank. How do you control that issue? Also, a source for your rod would help. Thanks in advance...........Tom

The "dip stick" has to be stiff and yet flexible enough to snake past the bend in the filler neck. A wooden dowel rod 1/8" diameter will work well. Use a lead pencil to make gallon marks. Gasoline will not wash off lead pencil mark. Round the bottom end of the dowel so it doesn't catch on any sharp edges. I marked my dip stick at same time I was calibrating Dynon fuel gage so my stick has marks every two gallons.
 
Great idea, and although I could not locate a 1/8" fiberglass rod, I did try other materials. The problem that I had was in getting a consistent reading due to the large filler tube allowing the bottom of the rod to drift to different locations on the bottom of the tank. How do you control that issue? Also, a source for your rod would help. Thanks in advance...........Tom

Tom, you should be able to find the fiberglass rod at Home Depot or Lowes (aviation department, of course!:D) . I got the idea from a security system installer who used it to thread wiring inside my house walls. The rod I bought was way too long and I cut it. You could do a second gauge with the left over! As for the routing, it seems consistent. I think that both the bend in the neck and the return fuel line which is somewhat in the way keep it always in the same place.
 
The "dip stick" has to be stiff and yet flexible enough to snake past the bend in the filler neck. A wooden dowel rod 1/8" diameter will work well. Use a lead pencil to make gallon marks. Gasoline will not wash off lead pencil mark. Round the bottom end of the dowel so it doesn't catch on any sharp edges. I marked my dip stick at same time I was calibrating Dynon fuel gage so my stick has marks every two gallons.

Jim, I think the rod is too thin to have a usable marking printed on. The measuring tape I sacrificed is convenient because it has got a stop at the end against which I push the rod. When taking a measurement I look at the place where the fiberglass stops shining and squeeze the rod at this location while pushing it against the stop: a cinch! Note that dipstick and tape are easy to carry in the center channel of the RV-12: when travelling you will always know what's left in your tank (Disclaimer: preferably after landing though!)

For the history, I got this idea from my first car when in college: a 1957 "Deux Chevaux" Citroen. It featured a dipstick for checking the quantity of gas in the tank! With my RV-12 rod, I feel much younger now!:cool:
 
I use a length of translucent brake line as a dip tube. I calibrated it at 5, 10 and 20 gal. The 10-20 mark is not linear because at about 19.8 gal you start filling the filler neck which causes a faster rise in level.

I posted the dimensions previously. I will remove my tank soon to do the bulkhead split, window replacement and bell crank bracket mods. When I refill I plan on adding a 15 gal mark.

The tube is nice because you can coil it into a 1 gallon plastic ziplock for travel, but it quickly straightens out and is stiff enough to give reliable readings.
 
The 10-20 mark is not linear because at about 19.8 gal you start filling the filler neck which causes a faster rise in level
This is visible at the bottom and top of the range on my picture of the tape. This is due to the shape of the fuel tank not being a true cube. It is why it is important to do the marking/calibration while doing a progressive filling of the tank. For those who don't bother doing the calibration, I can give you the points in inches for the quantities shown on my picture (i.e. if you use the standard VANs fuel tank). The mark TT means top of tank, whatever you add from this point will fill the neck.
 
I use a length of translucent brake line as a dip tube. I calibrated it at 5, 10 and 20 gal. The 10-20 mark is not linear because at about 19.8 gal you start filling the filler neck which causes a faster rise in level.

I posted the dimensions previously. I will remove my tank soon to do the bulkhead split, window replacement and bell crank bracket mods. When I refill I plan on adding a 15 gal mark.

The tube is nice because you can coil it into a 1 gallon plastic ziplock for travel, but it quickly straightens out and is stiff enough to give reliable readings.

Rich, window replacement. Rear turtle deck?
 
Jean Pierre,

I found the non-cube effect affects the first 5 gallons most. The filler neck effects the last 5 gallons.

Rich
 
Doug,

Yeah my rear window was the original flat lexan not the new molded window. It was crazed to the point I could feel the cracks on the outside surface with my thumbnail. At almost $400 delivered to me I am expecting much better life. I got 5 years out of the first window. If it doesn't do better I'll be getting my third window from the aviation department at Home Depot! I'm keeping the first window in case I need a pattern.

Rich
 
view


Keep this picture of the Moeller gauge dial with a Gallon scale with your Checklist:

view

Jean-Pierre, always wondered about calibrating the reliability of the Moeller gauge with the actual fuel in the tank. Based on your work, maybe a simple rule of thumb. "If the needle is above 1/2, the reading over estimates the actual fuel by about 1-2 gallons, below the 1/2 mark, its more close to the truth" Either way, I head for nearest runway when the needle is anywhere close to the 1/4 full mark. Thanks for doing/sharing this.
 
Jean-Pierre, always wondered about calibrating the reliability of the Moeller gauge with the actual fuel in the tank. Based on your work, maybe a simple rule of thumb. "If the needle is above 1/2, the reading over estimates the actual fuel by about 1-2 gallons, below the 1/2 mark, its more close to the truth" Either way, I head for nearest runway when the needle is anywhere close to the 1/4 full mark. Thanks for doing/sharing this.

Frankly, Brent I rely little on the Moeller reading, except to find if I made an error or if there is anything wrong with the other sensors/measurements.
We have three standard ways to evaluate the fuel tank level: computer flow, in-tank sensor displayed by Skyview and Moeller gauge. None is very precise and/or that reliable. It is why I loved the "never lying" windows and why I had to find a substitute with the dipstick. The calibration is easy for all but computer flow: start with an empty tank and go by 1, 2 or five gallons depending on how accurately you want to map the non linear shape of the tank as you mentioned. As for computer flow a lot has been written on this forum, I have nothing new to add. Of course above 14 or 15 gal., you are on your own as both floats hit the top of the tank way before it's full. Knowing exactly where you stand on the top 5 gallons is important for the computer flow derived fuel level, it's where the windows were useful and what you get back with the dipstick. After each flight I note the fuel levels provided by these 4 different sources which I recommend all RV-12 pilots to do: you will be amazed by the discrepancies you will find! Of course in case of discrepancy, the dipstick rules and it is also my source to enter in Skyview for the computer to use.
 
How precise do you really need to be?

I use the Moeller gauge mainly as a quick visual check pre-flight, to make sure the tank has what I think it has in it. If it's less than half full when I land, I fill it before flying again. When I fill it, I fill to the same point in teh filler neck so I know it's full. I've found the D180 indications -- both the float level once below 14 gallons, and the flow-calculated amount to be pretty accurate, within a couple tenths of a gallon.

Maybe I'm a little overly wussie about fuel reserves, but last weekend when I landed with about 4 gallons it was the lowest I'd ever gotten. I don't need to know the amount of fuel I'm carrying down to the ounce. I figure plus or minus a gallon or so is plenty accurate for the planning I do, and the D180 tracks it plus or minus about one or two tenths.
 
How precise do you really need to be?
.

You are probably right, Dale to question the need for accuracy for the type of flying we do in the RV-12. I have however found that since I have been involved in building an airplane and then flying it, even when unnecessary, precision does not hurt... plus, as the atheist said when caught praying: "you never know"...:D
 
Gotcha. I've never found an appreciable discrepancy between the two Dynon fuel quantity indications (float and calculated). I don't trust it completely, but I trust it more than I ever did the spam cans I used to fly. Those were good for a rough estimate only.

I don't miss the visual window at all. On my particular plane its only apparent function was to drip fuel into the carpet and under the baggage area floor. :eek: By the time I got it, the thing was mostly opaque and useless for seeing the fuel quantity. The Moeller gauge was a nice addition, allowing me to see the rough level while fueling.
 
In looking at Jean-Pierre's original title to this thread, I think the best compliment to the Moeller gauge is a rope. That's so when you throw it overboard to use as an anchor, you can haul it back up! :D

Okay, just kidding, but I've never found this gauge to be of any use whatsoever. I know you sealed up your sight gauge openings, but I still think this is the best way to confirm fuel level.

fueltank07.jpg


I also found that if you carefully calibrate the fuel sender, shaking the airplane after each 2 gallons, and then installing the sender so that it handles the bottom part of the tank all the way down, this is pretty accurate. I've flown down to 2 gallons or less a couple of times.

I've adjusted the fuel flow calibration a bunch of times but I always reset it during flight multiple times to what the fuel sender says.

Just my $.02.
 
... I've adjusted the fuel flow calibration a bunch of times but I always reset it during flight multiple times to what the fuel sender says.

Pretty much the same with me. My measured fuel quantity is consistently amazingly accurate. I mean accurate to a couple of tenths of a gallon or so accurate.

I rarely look at my Moeller gauge. The computed fuel flow reading is interesting but I know what my burn rate is and don't really need the readout.
 
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