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thinking out loud about dip stick fuel guages.

D

Dan_E_Root

Active Member
Your local pilot shops and catalog stores offers graduated dip stick gauges for fuel measurement for $12.00 or so. The universal gauge even comes with calibration instructions.

Why anyone would pay so much for a plastic tube with some markings on it?
I thought graduated laboratory pipets would be a good alternaive, but only found them in glass or polystyrene. Glass breaks, and the polystyrene probably breaks down in gas. Not to worry, that well-known purveyor of plastics whose name rhymes with ZAP sells acrylic piping. It's the same material the store-bought gauges are made from. OK, the pipe from RHYMES WITH ZAP has a thinner wall, and it's not graduated, which explains why the commercial ones go so high. I'll grant that the thicker rod stock guages will be sturdier over time, and they're already marked. They're very nice, but come on, twelve bucks?

On the other hand, you can get six feet of 1/4 inch OD, 1/16 inch wall pipe for ONE DOLLAR. Cut it to size, and calibrate to fit your plane. For a dollar, heck, you'll have enough material left over to make a handful of them. If one breaks, there's another ready to go. Give 'em away as stocking stuffers, or use 'em as swizzle sticks. Meanwhile, your friends will have replaced that storebought one at least once because the guy who borrowed it, lost it!

whaddya think. will this work?
blue skies.
 
Dan_E_Root said:
that well-known purveyor of plastics whose name rhymes with ZAP sells acrylic piping.
Click to expand...

I need more hints ... :confused: :confused:

Otherwise, sounds like a good idea!

Thomas
 
The dip sticks we use for the Katanas where I fly are wooden dowel, but instead of magic marker, each quarter-tank increment is marked on the dowel with a circular notch cut around the circumference (this way the markings don't wear off over time, and you don't get marker fluid dissolved in your fuel).
The wood gets wet when you dip it, which is what allows you to see how deeply the stick was in the fuel: you read the wet-line relative to the circular notches carved along the stick. Of course, with two tanks to check, this could be a problem unless the wood dries *very* fast. An alternative, perhaps more accurate approach would be to have a separate dip stick calabrated and marked for each fuel tank. Carve the letters "L" and "R" somewhere on the sticks to distinguish them.
 
prkaye said:
An alternative, perhaps more accurate approach would be to have a separate dip stick calabrated and marked for each fuel tank. Carve the letters "L" and "R" somewhere on the sticks to distinguish them.
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The wooden stick method sure works for me. Except I do not use a piece of dowel. Instead I use a wooden stir stick I got for free with my paint purchase at the local paint department of the hardware store. The paint department is right next to the aviation department. :D One of the advantages of the flat stick as opposed to the round dowel is I can calibrate and mark one side of the stick for the L tank and turn it over on the other side where it is calibrated for the R tank. As long as I make sure there is no user error by looking at the wrong side for the wrong tank, I get to use one stick that is calibrated correctly for both tanks. One stick with both tanks calibrated on it saves me from carrying around two sticks.
 
BTW and for the record, during tests at the local chem laboratory in the corner of my garage, I've proven conclusively that polystyrene pipets break down in 91 octane VALERO auto gas. One dip and the degradation begins immediately.

For those who want to more precisely measure tank volume, the dowel is less satisfactory cuz the gas wicks up the stick a little. If you've got a dip tube correctly calibrated you can get precise measurements.

Which begs the question, just how much precision do you need? For me, the question is how much money do I want to throw away? This tube gauge question came about because I didn't see the advantage in a twelve dollar graduated tube, when a stick would do just as well, in my mind. Obviously, there are some who like them, otherwise they wouldn't sell.

I like and use the wooden dowel too. Had a dowel laying around the shop. Pour in five gallons, measure and make a mark. Turn the marks into notches later. Cost me nothing but a little time.

The paint stirrer is an idea I'd not considered, but I like it because it satisfies my frugal tendencies.

cheers.
 
>> One stick with both tanks calibrated on it saves me from carrying around two sticks.

except once the stick is wet from dipping in the first tank, how do you see the new wet level after dipping in the second tank?
 
On my RV-6, when I look in the filler and the fuel is just at the bottom of the tank, there is eight gallons in the tank. After you fly your RV for awhile, you will be able to estimate the onboard fuel quite accurately just by eyeballing the tank. But anytime I begin a xcountry leg, the tanks get topped up. For local breakfast runs, I don't launch without 16 gallons in the plane (fuel at least above the bottom of the tanks).

So, all of this is sorta moot if you have a good fuel gauge like the EI unit which is accurate to about a gallon. More and more RVs now have fuel totalizers which adds even more precision to fuel management.

Personally, I have never found the need for a fuel dipstick--Maybe on a C152 where you can't see into the tank, but not on an RV. :)
 
Fuel dip stick

Make a dip stick long enough so that you can use 1 end for the left tank and then flip the stick over and use the other end for the right. I stick to measure both tanks.

Jim Streit
RV9A
 
Dan_E_Root said:
For those who want to more precisely measure tank volume, the dowel is less satisfactory cuz the gas wicks up the stick a little. If you've got a dip tube correctly calibrated you can get precise measurements.

Which begs the question, just how much precision do you need?
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I had the wooden dowel dipstick for my Citabria and it did wick up the stick, but only 1/8" or so, and certainly not enough to affect any decisions about fuel I may have made.
 
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prkaye said:
except once the stick is wet from dipping in the first tank, how do you see the new wet level after dipping in the second tank?
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Let it dry. It only takes a few seconds around our 100+ degree days here. Perhaps a minute if you don't live in the bowels of HE**. :D
 
100 LL dries fast

You only need one end for a dipstick, it dries fast.
Sharpen the other end like a pencil and use it to open the fuel caps.
 
Ok - I'm stupid - what am I missing?

Why, if the tanks are the same size, do you need a different dip stick for each tank? If there were 10 gallons in each tank, wouldn't the dip stick (or what ever) read the same when checking both tanks?

The RV-9 has two 18 gallon tanks. If there are nine gallons in the left tank and the stick gets wet to a certain point, shouldn't it get wet to the same exact place if the right tank has nine gallons?
 
Robert M said:
Ok - I'm stupid - what am I missing?

Why, if the tanks are the same size, do you need a different dip stick for each tank? If there were 10 gallons in each tank, wouldn't the dip stick (or what ever) read the same when checking both tanks?
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I use my left eye on my left tank and right eye on the right tank!! Helps prevent parallax errors. :D
 
I'm curious, because the wing (and therefore tank) are on a dihedral, how much fuel is in the tank when the dip stick comes out dry?
 
Av8torTom said:
I'm curious, because the wing (and therefore tank) are on a dihedral, how much fuel is in the tank when the dip stick comes out dry?
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As Ralph said, it's probably best to test yours specifically when you do your fuel gauge calibration to account for any manufacturing discrepancies between tanks or whatever, but on my RV7 taildragger, when I can see gas just starting to cover the bottom skin under the filler I have about 5-6 gallons in there.
 
I've always wondered why people think the dipstick has to go in vertically. I angle mine to the back of the tank and calibrated it by adding 2 gallons at a time to an empty tank. I can easily measure to 2 gallons but if I go vertically, when it gets down below 10 gallons or so it no longer reads anything. I'm sorry the images are so large.
20240712_105924.jpg


20240712_105915.jpg
 
Hangar 1271 said:
I've always wondered why people think the dipstick has to go in vertically. I angle mine to the back of the tank and calibrated it by adding 2 gallons at a time to an empty tank. I can easily measure to 2 gallons but if I go vertically, when it gets down below 10 gallons or so it no longer reads anything. I'm sorry the images are so large. View attachment 66389

View attachment 66388
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Hi
I think you have a RV8? Right?
Next time your fuel level is at the bottom level of your fuel stick, maybe drain that tank & confirm your stick is accurate. I think you will find you have more fuel than you think.
 
Ralph Inkster said:
Hi
I think you have a RV8? Right?
Next time your fuel level is at the bottom level of your fuel stick, maybe drain that tank & confirm your stick is accurate. I think you will find you have more fuel than you think.
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I rarely (read as never) get that low but I did calibrate it at an angle. It probably isn't perfect but it is pretty close.
 
I like having multiple uses for things so I got two of the plexiglass “Snapper” gizmos from AntiSplat and calibrated them, Marked with a chisel making a real visible mark every two gallons. Then drilled a very small hole which makes the gas level easier to see in bright light. They live in the armrest on each side of the cabin and easy to reach for dipping tanks or their intended use of snapping pieces off a busted canopy while upside down hoping for egress. Two of them makes a better chance of finding one when needed. The new ones have a gas cap lever lifter which probably doubles as a beer bottle opener. That’s four uses for one length of shaped aluminum. ;)
 
Sam Buchanan said:
So, all of this is sorta moot if you have a good fuel gauge like the EI unit which is accurate to about a gallon. More and more RVs now have fuel totalizers which adds even more precision to fuel management.

Personally, I have never found the need for a fuel dipstick--Maybe on a C152 where you can't see into the tank, but not on an RV. :)
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I’m with Sam; with having a fuel totalizer, eyeballs and accurate gauges, I’ve never felt the need for a dipstick on my RV. Now if I’m flying a DC-3 with four 200 gallon tanks and crappy gauges, then yep, gimme that fuel stick!
 
As mentioned, it’s wise to do your own calibrations on your airplane.
I don’t use one in the 6 per Sam’s post. Never had the need.

The Bucker has a bobber. I use an acrylic tube that has engraved markings. Any cheapo engraver would work, if you must…..
 
Snowflake said:
FWIW, I used a sharpie to write the numbers directly on the acrylic tube. I've "freshened" the numbers twice in 15 years.
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Certainly many great ways to accomplish this simple device. I'm sure a rigid acrylic tube would work just fine, but mine isn't acrylic, it's just plain old polyethylene fuel tubing zip tied to some scrap aluminum. It's notched at various points as reference. From previous threads on this issue and others posting their calibrations, I note that no two such tubes seem to be the same, at least don't match mine, but I calibrated it myself at the same time I calibrated my fuel tanks for a new EFIS, two gallons at a time per tank, and it matches my fuel gauges and fuel computer perfectly.
 
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Between the fuel totalizer function, the very accurate capacitive fuel level gauges, and my Mk. I eyeballs, no need for any sort of dipstick on my 7A.
 
The benefit of a paint stir stick is that they're free and you can pick up a handful of them from any paint store. They're all the same size and you can create multiple copies of the calibrated stick in just a couple minutes with nothing more than a Sharpie.

If one gets lost (been there/done that) or broken (ditto), you have many backups ready to go. Cost: $0.00.

--Ron
 
RV7A Flyer said:
Between the fuel totalizer function, the very accurate capacitive fuel level gauges, and my Mk. I eyeballs, no need for any sort of dipstick on my 7A.
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Mine are both very accurate too, I just hate to rely solely on occasionally problematic capacitive fuel senders and a computer that relies on human input to be an accurate evaluation of something as important as how much fuel I have on board. A dipstick is just a cheap, simple, non-mechanical/non-electronic way of confirming that the fuel senders and EFIS electronic totalizer are still functioning accurately. Costs about a dollar to make and adds about 15 seconds to a pre-flight, but it gives me peace of mind to know that my fuel gauges/computer are in the ballpark.
 
JonJay said:
As mentioned, it’s wise to do your own calibrations on your airplane.
I don’t use one in the 6 per Sam’s post. Never had the need.

The Bucker has a bobber. I use an acrylic tube that has engraved markings. Any cheapo engraver would work, if you must…..
Click to expand...
Tanks from the same model should be the same.
 
Robert M said:
Ok - I'm stupid - what am I missing?

Why, if the tanks are the same size, do you need a different dip stick for each tank? If there were 10 gallons in each tank, wouldn't the dip stick (or what ever) read the same when checking both tanks?

The RV-9 has two 18 gallon tanks. If there are nine gallons in the left tank and the stick gets wet to a certain point, shouldn't it get wet to the same exact place if the right tank has nine gallons?
Click to expand...
You’re not stupid.. but the first time you use the wooden stick, you’ll get it. What they are referring to is that after you dip the first tank, the stick is wet and it’s hard to get a reading on the second tank.. but if you walk over slow and waive the stick a little, it dries fast and you can then dip the second tank.
 
maxmirot said:
Tanks from the same model should be the same.
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Seems like that would be a logical assumption but I haven't found other published dipstick calibrations for RV-9A's to be accurate on my RV-9A. The one that I calibrated is dead-on accurate, so I haven't spent any time pondering the reasons for discrepancy.
 
I have never trusted fuel gauges since the time one stuck and I nearly run out of fuel. The gauge was the most simplest type of a float and wire through the filler cap.
I was towing gliders and noticed the gauge was not moving as I landed and taxied.
I would have run out on the next tow.

Now I only use only a gauge as a guide.
For the RV 3 I have a very accurate dip stick and make sure I have enough for the flight plus plenty of reserve.
I also monitor the flight time / fuel use.

My university buddy and best man at my wedding ran out of fuel and safely carried out a dead stick into a field, and the fuel gauge was reading 1/4 full in an aircraft he had hired.

See you at Oshkosh

Rob
RV 3 G-BVDC
 
Dipping the tanks is part of doing a deliberate preflight; not just going through the motions. Just looking at stuff can become mechanical and so routine you do not pay attention. It is similar to running fingers across stuff you look at (which I also do during a preflight) to get a tactical feel of what you are inspecting.
Plus it takes 5 seconds per tank.
 
Sam Buchanan said:
Before every flight I open the fuel caps and check fuel level with an eyecrometer......quick, easy and reliable. ;)
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My eyecrometer is quick and easy, but I don't know about reliable ;). It's accurate enough to tell me if there's fuel in there, but not how much. I'd rather take the extra 15 seconds with a dipstick so that I have something to determine whether or not my less-reliable electronic gauges are still in the game.
 
JonJay said:
“Should” , yes….. I would be checking mine but that’s me.
Do you guys calibrate your stick with consideration for unusable fuel? Curios.
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I never thought of it. But I was starting with an empty tank with a smidgen of fuel after I drained the tank. At 5 gallons in the RV8, my fuel stick only registers less than 1/2".
 
MacCool said:
Seems like that would be a logical assumption but I haven't found other published dipstick calibrations for RV-9A's to be accurate on my RV-9A. The one that I calibrated is dead-on accurate, so I haven't spent any time pondering the reasons for discrepancy.
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I'm sure they all think that as well. But the reality is that if you have all built to plans, the variation in dipsticks couldn't be more than half a litre unless you've *really* gobbed on the proseal, or you've figured out where that lost rivet gun ended up...

The most likely reason is that everybody "calibrates" their dipstick in different ways. A wooden dipstick might be calibrated, but did the calibrator take into account the seepage in the grain? And an acrylic tube might be calibrated but is it calibrated to mark the top of the meniscus, or the flat surface of the fuel? And Is it being used "vertical" (who carries a level to make sure) and is it being used at the front of the fuel cap opening or the back? Of course, TW vs NW will read differently as well just due to tank angle.

It definitely is possible to sell a stock dipstick for a stock RV. It needs to come with instructions that cover how to position it when taking a reading. I suspect the same is true for a Cessna, although their tanks generally have less dihedral and are more rectangular.
 
MacCool said:
My eyecrometer is quick and easy, but I don't know about reliable ;). It's accurate enough to tell me if there's fuel in there, but not how much. I'd rather take the extra 15 seconds with a dipstick so that I have something to determine whether or not my less-reliable electronic gauges are still in the game.
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Maybe my eyecrometer has been refined over time, been flying the RV-6 since 1999, the eyecrometer is good to within a gallon or so down to six gallons, I don't launch with that small amount in the tank.

Another thought, the aircraft must be very level for either the eyecrometer or dip stick to be accurate. The taxiway outside my hangar has a slight crown and that is enough to effect fuel level readings.
 
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Snowflake said:
I'm sure they all think that as well. But the reality is that if you have all built to plans, the variation in dipsticks couldn't be more than half a litre unless you've *really* gobbed on the proseal, or you've figured out where that lost rivet gun ended up...

The most likely reason is that everybody "calibrates" their dipstick in different ways. A wooden dipstick might be calibrated, but did the calibrator take into account the seepage in the grain? And an acrylic tube might be calibrated but is it calibrated to mark the top of the meniscus, or the flat surface of the fuel? And Is it being used "vertical" (who carries a level to make sure) and is it being used at the front of the fuel cap opening or the back? Of course, TW vs NW will read differently as well just due to tank angle.

It definitely is possible to sell a stock dipstick for a stock RV. It needs to come with instructions that cover how to position it when taking a reading. I suspect the same is true for a Cessna, although their tanks generally have less dihedral and are more rectangular.
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I dunno. I'm sure it's all something like that but not something that I ponder as I have a system that works fine. I didn't build my airplane and have no clue as to how the tanks were built, only that they're both 18 gallons, don't leak, and I always know how much fuel I have in them. Next problem.... :)
 
Snowflake said:
...did the calibrator take into account the seepage in the grain? And an acrylic tube might be calibrated but is it calibrated to mark the top of the meniscus, or the flat surface of the fuel? And Is it being used "vertical" (who carries a level to make sure) and is it being used at the front of the fuel cap opening or the back? Of course, TW vs NW will read differently as well just due to tank angle.
Click to expand...
Forgot to mention, if it's a wood stick marked with a Sharpie, the thickness of the ink line....

If you have to take any of these into account lest you get so low that you risk running out of fuel, I'd say there's a different problem...
 
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A little more expensive that making your own but I got one of these that was pre calibrated for the RV-8 and it is “dead on balls accurate”. Although my fuel gauges in the EFIS themselves aren’t that accurate above 15 gallons, the totalizer matches the fuel stick totals exactly every time.

www.aircraftspruce.com

Fuel Stik For RVAircraft | Aircraft Spruce

Fuel Stik For RVAircraft Extremely light, high impact plastic tubing with aluminum rings resist damage.
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Mine was simil
PhatRV said:
I never thought of it. But I was starting with an empty tank with a smidgen of fuel after I drained the tank. At 5 gallons in the RV8, my fuel stick only registers less than 1/2".
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Mine was similar on my RV6, except that mine had 4 gallons when it started registering on the stick (stick against the aft rim of the filler opening with stick straight up and down). So I made a line there and marked it “4”. Add 2 gallons, mark “6”, etc. I don’t know what my unusable fuel is, but assume 1 gallon in each tank, and I plan accordingly. My min fuel on board for comfort is 10 gallons (VFR), so I have a little leeway. When going cross country, I fill it all the way up, but instead of setting my totalizer to 38, I can set it to 36 to account for unusable fuel because my totalizer is very accurate. I haven’t actually done that, but I guess I could if I was feeling math challenged. In truth my bladder gets full long before my tanks get empty. The stick comes in handy when doing formation flying with less than full tanks, or anytime I do acro. Even though my plane is relatively light (1042), if I have more than 22 gallons onboard I’ll exceed my 1375 aerobatic gross weight limit, and that is of course solo.
 
I had to remove a tank on the RV6 due to a duck strike (it's in the archives....) and when I drained the tank I found it had practically no unusable fuel. But for me that is a moot point, I don't want either tank anywhere close to that level in case something happens to the vent for the tank with fuel.
 
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