Fuel Height Question - Dipstick/fuel tab

Anyone out there with a flying (or at least completed and fuel-filled) -10 that has related the fuel quantity to height inside the tank with the aircraft sitting level (i.e. a calibrated dipstick or something)? I'm about to finish up my fuel tanks and wanting to install a fuel tab. It would be nice to calibrate it so that it would show approximately 2/3 full (20 gal) like some production aircraft. I'd take a stab in the dark at this but thought I'd see if someone might know how far up from the outboard bottom tank skin 20 gallons is? Appreciate any help in advance! -Mike

Maybe

I may have this data somewhere from when I was calibrating fuel tanks. I'll let you know if I find it.

I used a paint stick, put in fuel at 5 gal increments -------(takes apx 10 gal to get to the filler for the first mark, due to dihedral)-------and marked the stick at each additional 5 gal level.

Make a second stick and put it somewhere you can find it after you loose the first one.

I used a file to notch the stick at each level, still gives a reference mark if you happen to use a pen instead of a pencil to mark the stick.

Thanks for the responses Bryan and Mike... I think I'm just gonna go ahead with my guesstimate of where the tab should be. I prototyped a tab that goes 3-5/8" down from the top of the tank, which is a little past the 1/3 point in height (9" tank height).

I suspect that filling to the tabs will be *at least* 20 gallons in this configuration, likely closer to 22 or 23. That should work fine, and if it doesn't, well... we'll figure something else out

Any last words before I put the baffles on, entombing our hard work and proseal goopiness forever?!?

Thanks again guys! -Mike

I used one of these:

http://www.sportys.com/pilotshop/universal-fuel-gauge-26-in.html



I then filled the tanks five gallons at a time and calibrated the stick.

I have the measurements at the hangar, but it would be easy enough to translate the markings on the stick to inches.

I made my own Fuel Hawk style dip indicator out of clear Lexan tubing. I strapped a steel machinist ruler to it and recorded the measurements at 2.5 gallon increments. I then used a fine point sharpie and made a mark on the tubing when I was done. Removed the ruler, chucked in my lathe and cut a fine V line at the marks. I then engraved the gallons at each mark. I made two of them and keep one in the plane at all times. I always dip during preflight. You don't want to guess on where you put the 20 gallon tab marker. There is a huge difference in the marking heights as the tank fills up due to the wings dihedral. I'll get the exact measurement for you tonight.

I am using a new fuel measurement system made by CiesCorp: https://www.ciescorp.net/vans-rv-fuel-level.html

It uses senders at both ends of the tank (upper/lower) with a control wire between them. This allow complete fuel management for the entire fuel tank fill. The senders provide signal that integrates with with the G3x (0-5v).

I built a tab into my tank and frankly I just guesstimated (https://myrv10factory.wordpress.com/2011/05/11/finishing-the-leading-edge-skins-and-tank-building/). This tab wound up being 25 gallons and measured 3.5". Pictures on the link above.

As I prepared the tank, I decided to add a minor modification from a plane I fly now. The Piper Arrow has a ?dipstick? permanently mounted inside the fuel cap area that show when the tanks are about 2/3 full. This helps as its not always possible to fly with full tanks, so this quick gauge lets you look in and see where you are for a less than full fuel run. It was some .040″ stock cut to about 1″ wide and then bent to fit next to the fuel cap flange and then extend down about 3.5″ and then bend the other way for easy visual spotting.

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Wow thanks again guys for the additional responses! David C- really appreciate your offer! Please don't go out of your way too much for us, like making a special trip to the hangar or something, but certainly if you have plans to be around the plane tonight I'd sure be curious what the measurements are!

BTW- I'm not overly concerned at hitting 20 gallons "to the drop"... as Mark said, he guesstimated his and ended up with around 25 gals. That would be fine with me also, just to have a good reference point with less-than-full tanks to do a quick w&b if we're loading up to head somewhere, and make it easy for whoever is filling the tanks. Ideally, closer to 20 would be great but I'd hate for someone to really go out of their way to get me those numbers.

Appreciate it as always!

Here is a couple pictures of my homemade Fuel Hawk style dip stick. The black lines from left to right indicate 1/4, 1/2, 3/4, Full. The stick is calibrated in 2.5 gallon increments so you can see that the dihedral of the wing effects the spacing quite a bit. My 20 gallon mark is exactly 4.00 inches from the bottom of the tank. I calibrated mine from the inboard edge of my filler cap flange. No problem getting this for you Mike as I went to the hanger today to clean up the mess I had made.

Thanks!!!!!

David-- thanks so much! Really appreciate you doing that. Since the tank is about 9" high, I'll re-make my tab tonight to be 4-7/8" long (1/8" flange thickness), which ought to do the trick. Once I get it done I'll post pics and an update on my blog too, for anyone interested.

Really looking forward to being done with these tanks... fingers crossed for no leaks!!!!

Cheers, -Mike

Mike,

Can you share how the tabs worked out? Has anyone got a calibration record of their tanks from bottom to top at the outboard edge to share? Unfortunately the pictures posted by David before are no longer available.

I have an idea for a tab with multiple graduations on it and would like to install it before I close up the tanks for good. I want to just bond the tab to the outboard rib to avoid having to drill out and re-rivet the fuel cap.

I just started flying this week... thinking back on everything, what I REALLY should have done was just gotten some kind of dipstick that i could have easily calibrated while i was putting 5 gallons in at a time to calibrate my floats.

cderk said:

I just started flying this week... thinking back on everything, what I REALLY should have done was just gotten some kind of dipstick that i could have easily calibrated while i was putting 5 gallons in at a time to calibrate my floats.

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I did that last year on my Mooney 201 that I bought (no one makes a pre-calibrated stick for the M20 series because of the variation in tanks including many that have bladders). Took a while to accomplish, but worth it. I'd like to put some tabs with multiple graduations on them in the RV-10 tanks to make the process easier, and give the person filling the tank a quick reference point.

Oh, and congratulations! I watched your first flight video and loved it.

I made some measurements on my 7 level, and sitting, when doing a 2 gallon calibration. I measured with a stick with a small ID tube attached, recording distance from the bottom. Dipsticks made from a dowel rod, a clear tube with an aluminum strip attached were tried and not easy to use or inaccurate. Finally saw a post that used an aluminum stick with holes. I made mine to indicate each 1/2 gal. The holes are staggered side to sideband it works perfectly. The wick effect of anything that goes in the fuel is way higher than the actual level and adversely affected the usability and accuracy. In 100 hrs of recording, the total fill is within 1/2 gal of the dip stick and the totalizer in the G3X. The holes are smaller than 0.063" and it is easy, in all light conditions, to read. You can test the hole size for yourself in a clear glass of fuel to determine what is best. And compared to alternate methods. I hold against the leading side of the fill opening and aft of the internal stiffener.

My strip is alodined .025" X 3/8" and attached to a keychain. Light weight too.

The worst part was wearing the headband magnifier and a vibratory etcher to write the tiny numbers on the stick! If it folded and fit in a shirt pocket it would be perfect, but I have found no elegant way of achieving that yet. Maybe in the shutdown.

One last thing - the absolute reading of a single tank is less than 1/2gal accuracy, but the total of both seems to make up for a tilt one way or the other.

Here's a quick sketch of what I am thinking of. I would bond it to the inside of the outboard tank rib with tank sealant.

Seems like a dip stick would be easier— I bought the one from ACS but truth in lending I’ve never taken it out of the tube since I bought it over 5 years ago. How often do you think you’ll need to partial fuel to something other than full?

Auburntsts said:

Seems like a dip stick would be easier— I bought the one from ACS but truth in lending I’ve never taken it out of the tube since I bought it over 5 years ago. How often do you think you’ll need to partial fuel to something other than full?

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I use a dipstick before every flight to keep track of my fuel usage and verify my flowmeter on the Mooney. I spent several hours calibrating the Mooney dipstick and I will do it again for the RV-10, but I think this tab option will give me a very quick and easy idea of the actual fuel in the tank *while filling it*.

I love instrumentation, but I "trust but verify" every time I go for a flight.

I really want to make this tab deal, it will literally take me 10 minutes to make two of them with a shear, bandsaw and bending brake once I have the dimensions.

Fair enough. I back up my instruments with time and known fuel flow at various power settings, but to each his own. I verify by comparing what the system or my math says I burned to what the fuel pump says I did when I gas up.