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RV-8 fuel tank dipstick

Paint Stir Stick - $0.25

Shorten as appropriate. Mark two gallon increments in permanent marker (one side of the stick for each tank).

Cheers, David
 
I recently saw a fuel "dipstick" which was integrated right into a standard Vans fuel cap. I'm not 100% sure how it was accomplished but I plan to figure it out (or reverse engineer it) one of these days.
 
Would love to have measurements. Thanks!!!!!

I agree! Maybe a picture of the stirrer with a yard stick/tape measure next to it, if you could. Also, do you measure from the forward or aft side of the fuel cap opening?

Thanks.
John
 
I agree! Maybe a picture of the stirrer with a yard stick/tape measure next to it, if you could. Also, do you measure from the forward or aft side of the fuel cap opening?

Thanks.
John

I'll add the photo tonight showing the measurements. To maintain consistent readings I place the clear straw like stick down against the "L" skin stiffener that is on the tank bottom and just behind the filler neck, with the stick against the aft side if the filler neck, I then put my finger over the "straw" end and pull up for reading...(Sorry, Dip Stick 101 may not be needed). ;)
"IF" your pre punched wing is the same as mine your results should be the same, but worth double checking a few times...no warranty expressed or implied.
 
CAUTION: Dip Stick Pics

One more variable; -8 vs -8A....my tail rests on a little wheel.

And...my dip stick is calibrated for "total Fuel". Not "useable fuel".

Moral of the story: never use someone else's dip stick for your dirty work...rather it be wood, plastic, or other.

keurdh.jpg


Oh, and proof I wasn't measuring my dip stick all night.

2jd0sjd.jpg
 
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The builder of my plane used a 1/2" square piece of wood to create a combination filler cap remover/dipstick. Each tank is marked off on opposite sides of the stick in 2-3 gallon increments. Nothing fancy but it works perfectly.
 
I?ve made dip sticks for all my RV?s - RV6, RV8 (2), and my current RV4. Marks every 2 gallons. I used a half inch wide piece of oak on most of them (the end of which is shaped to open the fuel tank cap), and one of those plastic tubes from Sporty?s for the latest one. I measure by putting the dipstick at the back edge of the fuel opening and as nearly vertical as I can make it. After a little tweaking, it?s quite accurate.
 
Scott makes a good point about defining a specific spot & angle to measure from.
I buy a 3/4" x 30" dowel from Lowes aviation dept. and make a few copies of the calibrated sticks (specific to each plane), nice to have a few extras to replace the ones I loose along the way. I mark them with a little band saw cut every 5 gallons.
 
I've found with wooden sticks that the fuel wicks up the stick so you get different readings depending on how long it's in the fuel.
Here's what works good for me. Paint the stick. Dark colors work better. I like red. Mark your increments and gallons with a sharpie. Now coat the stick with a layer of epoxy. Cheap 5 min epoxy works fine. Then scuff it with scotchbrite to a dull finish. The wet part looks shiny. Very easy to read.
 
The builder of my plane used a 1/2" square piece of wood to create a combination filler cap remover/dipstick. Each tank is marked off on opposite sides of the stick in 2-3 gallon increments. Nothing fancy but it works perfectly.

If you compare the markings for the two tanks, are they different? why?
 
I purchased a fuel dipstick from Aircraft Spruce. It's the Fuel Hawk 11" gauge. See here: https://www.aircraftspruce.com/catalog/pspages/fuelhawkuniv11.php

In my RV-8 it's a basic setup with the tanks and a forward "tab" right under the fuel inlet. I use the exact same location to check the fuel level every time - right against the aft wall of the tab (pushing forward on it) and the fuel dipstick pushing on the forward wall of the fuel tank opening wall. This is my "datum". On a full tank (appx 21 Gal) I measure the "units" on the stick. At some point the tank will run dry on the lower floor of the tank at the tab. This reads "0" units on the stick, of course. Of course, also, with zero units, there is still fuel available in the tank. Each airplane will be slightly different, you just have to know how your tank reads between the tab stick reading location being at "0" units and the tab stick reading location being "whatever units" that a full tank gives. Over time, each time you fill up, you take a pre-fill reading of how many "units" you measure before fill-up. Then watch closely at how many gallons go into each tank to fill up. You take down those data points. The Universal Stick reader instructions show you how to plot your tank readings to get useful gallons-per-stick unit.

As guys here say in the thread - you can use wood sticks, metal, etc. It's not magic. But the plug and play solution from Spruce is easy and relatively cheap.

By the way, due to how your airplane "sits" on the ramp, ramp true level (no ramp is truely level), and other things like where exactly your tab is on the tank, how carefully you hold your stick when you take your unit measurements - these all mean tank readings are approximations - and totally custom for each experimental aircraft in question (I suspect there might be enough difference from a buddy's RV-8 plot for example, that it is probably prudent to take the data for your own plane). The accuracy is good though once you get your data points, give or take a gallon or so in my experience. And also, the right tank will tend to read slightly different than the left in my experience (probably a slight difference in tab location so the reading can be slightly off from tank to tank). You could be anal retentive and take data for each tank and that would give you more accurate measurements but because I know this is an approximation, I use general "units per gallon" and keep it simple so that there is less of a chance of human error in reading the tanks.

It took me about 10 flights to get a confident feel for where my fuel was on what reading. Obviously taking measurements at different tank levels is important to fine tune your "curve" that you use as an interpretation of the unit measurements. I have enough confidence in the system now that I use it as an operational planning tool for less than full fuel tank departures and I depart at less than full tanks all the time now with complete confidence without sole reliance on potentially inaccurate fuel gauges (depending on type) as long as I dip the tanks and plan accordingly. On fill up, the readings produce very close approximations to my expected gallon uplift per tank.
 
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My tank has 3 gallons left when the dipstick stops ?getting wet?, so that?s what it says at the bottom of the stick - 3 gallons. Below that is a guess if you care to takeoff on that tank..... I don?t. Both tanks are exactly the same unless parked on a Left/right slope.
 
Scott makes a good point about defining a specific spot & angle to measure from.
I buy a 3/4" x 30" dowel from Lowes aviation dept. and make a few copies of the calibrated sticks (specific to each plane), nice to have a few extras to replace the ones I loose along the way. I mark them with a little band saw cut every 5 gallons.

+1

Very little wicking w/o painting. Marked with a Sharpie in 2 gal increments.

Dipped before each flight and am amazed how accurate it is comparing to my D-180 fuel counter. Limit boost pump usage to maintain accuracy between the two.
 
Looking good Bruce. Does the Sharpie marker stay readable over time with the constant exposure to 100LL? I'm at the point now where I'm ready to mark down the gallons available from all the data I've taken over the last 5 months. That will complete the data collection exercise that I've still been meticulously doing. Time to turn that fuel stick into a "Dummy Dip Stick". :)
 
There is an odd paradox at work here:

there seems to be a lot of concern for precisely positioning the dip stick, concern that one tank would be different from another, concern that one airplane might be different from another.

And yet, we then treat this measurement as an approximation with a lot of conservatism about using the information.

If it is going to be treated as an approximation, then why work so hard to get precise data?

I took the readings off of Bruce's photo of his dipstick ( thanks Bruce for updating the picture :) ) and plotted it. I was interested to see how non-linear the curve would be, which would be expected because of the odd shape of the tank. The curve is surprisingly linear, although it is convex upward everywhere. The curve being fairly close to linear, it is also possible to extrapolate Bruce's curve to the zero point. His curve shows 2 gallons at zero on the stick.

So how linear is it? Well, if instead of using the measurements and data, you were to simply mark a stick with linear graduations from 0" =2 gallons to 6 3/4" = 21 gallons (0.35" per gallon), you would have a dip stick that reads within ONE GALLON of correct at all tank levels. And because the actual curve is convex, the linear curve always reads low (conservative).

Depending on how you set your mixture, this allows you to estimate your endurance to within 6--8 minutes. No one is going to flight plan to an expected precision of 6--8 minutes of endurance--we keep more than 30 minutes reserve.

I would be satisfied to just make a stick with that linear graduation and use it straight away.

Caveat: Bruce's data is from an RV-8. I have an RV8. The stick as I describe may not be within one gallon of correct on an RV-8A, or on an RV-7, etc. because the zero-point fuel quantity may be different. But if you can establish what your zero-point fuel quantity is, you can then make a linear stick for your model. We know what the full-point value is.
 
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Yes I agree Steve, the dipstick only deserves a few minutes in the making. I made mine as I first filled the tanks 7 years ago. Much more time was spent calibrating, testing and recalibrating the fuel flow and fuel level sensors. But I always used the dip stick for the final word (which matched the fuel top-off calculation closely)

The sharpie marker will only fade over a few years, I have wrote over them twice in 7 years is all.

Cheers to Steve for simplifying this process below just like an engineer can! 😀

There is an odd paradox at work here:

there seems to be a lot of concern for precisely positioning the dip stick, concern that one tank would be different from another, concern that one airplane might be different from another.

And yet, we then treat this measurement as an approximation with a lot of conservatism about using the information.

If it is going to be treated as an approximation, then why work so hard to get precise data?

I took the readings off of Bruce's photo of his dipstick ( thanks Bruce for updating the picture :) ) and plotted it. I was interested to see how non-linear the curve would be, which would be expected because of the odd shape of the tank. The curve is surprisingly linear, although it is convex upward everywhere. The curve being fairly close to linear, it is also possible to extrapolate Bruce's curve to the zero point. His curve shows 2 gallons at zero on the stick.

So how linear is it? Well, if instead of using the measurements and data, you were to simply mark a stick with linear graduations from 0" =2 gallons to 6 3/4" = 21 gallons (0.35" per gallon), you would have a dip stick that reads within ONE GALLON of correct at all tank levels. And because the actual curve is convex, the linear curve always reads low (conservative).

Depending on how you set your mixture, this allows you to estimate your endurance to within 6--8 minutes. No one is going to flight plan to an expected precision of 6--8 minutes of endurance--we keep more than 30 minutes reserve.

I would be satisfied to just make a stick with that linear graduation and use it straight away.

Caveat: Bruce's data is from an RV-8. I have an RV8. The stick as I describe may not be within one gallon of correct on an RV-8A, or on an RV-7, etc. because the zero-point fuel quantity may be different. But if you can establish what your zero-point fuel quantity is, you can then make a linear stick for your model. We know what the full-point value is.
 
Thanks to all. I had one with my last 8 but it went to Germany with it when I sold it. Hopefully picking up our new 8 this week and this will provide a double check on gages that are new to me.
 
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