Fuel Stick - Usable vs Total

Which scale should be on a Fuel Tank Dip Stick

  • Usable

    Votes: 26 59.1%

  • Total

    Votes: 15 34.1%

  • Both

    Votes: 3 6.8%
  • Total voters
    44
Honest question. Is there a fuel stick that is not marked that I can put the measurements of my "highly calibrated broken ruler" on to use going forward?

I don't think I'll find a properly marked stick for an RV at sporty's.
 
Ravioli said:
Honest question. Is there a fuel stick that is not marked that I can put the measurements of my "highly calibrated broken ruler" on to use going forward?

I don't think I'll find a properly marked stick for an RV at sporty's.
Click to expand...

Use a wood dowel from the aviation isle at Home Depot.
 
Ravioli said:
Honest question. Is there a fuel stick that is not marked that I can put the measurements of my "highly calibrated broken ruler" on to use going forward?

I don't think I'll find a properly marked stick for an RV at sporty's.
Click to expand...

Sporty's comes through, sort of:

https://www.sportys.com/pilotshop/universal-fuel-gauge-11-in.html

It has markings, but you have to calibrate it yourself. It's the same as the other Fuelhawk dipsticks, dip it then hold your thumb over the top.

Otherwise, a wood ruler, paint stick, or dowel seems to work.
 
Matthew said:
It has markings, but you have to calibrate it yourself...Otherwise, a wood ruler, paint stick, or dowel seems to work.
Click to expand...
Should I calibrate them for total or usable fuel? Maybe someone should start a poll. ;)

Nauga,
full-circle
 
Hi Guys, let me try and get this question back on track because there are a lot of tangents in this thread.

#1 - Don't get hung up on the fact that it's a C-172P, I need to make a few more for other airplanes on the ramp so aircraft model is irrelevant.

#2 - I know how to make a fuel dip stick so no need to post instructions on how to calibrate one, what materials to use, etc.

#3 - The only difference between putting Usable vs Total Fuel on the stick is the number written next to the lines. So for example, if an aircraft has 13 gallons total per tank but only 12 gallons usable per tank, then the top line indicating FULL on the dip stick would say 13 if I go with Total fuel, and 12 if I go with Usable.

To Clarify - My question is which number, Total or Usable, is better to have on a fuel stick? For example, which one is better for calculating fuel burn? Which fuel number do you guys use for flight planning and should the number on the fuel stick match the calculations on your flight plan, or weight and balance, or does it have no impact? What do most GA aircraft gauges allegedly show (usable I think) and would it be better if that matched the stick? Dipping the fuel and seeing Total, might mean someone makes a mistake and thinks they have more fuel in the tank than they actually do. These are the types of questions I'm trying to weigh the pros and cons of because I've heard arguments that TOTAL is better for accurate and faster planning and calculations but Usable is more relevant and applicable in daily life.
 
?

For a fuel stick, why would you care how much unusable fuel is in the tank since you can't use it anyway? There will be a fuel level displayed on the stick - below that level is EMPTY, so why not mark the stick that way, too? Otherwise you're doing too much mental work and your fuel stick won't match anyone else's, and that's where mistakes are made. You could stick the tanks, see "10 gal" on the stick, forgetting that it's actually 8 gal (if 2 are unusable) because you got distracted and forgot to do the math. I wouldn't even put 2 different sets of marks on it.

Why is TOTAL better for "...accurate and faster planning and calculations..."? If you want TOTAL, add 2 (or whatever), but don't use it for your fuel planning.
 
SONICMASD said:
Hi Guys, let me try and get this question back on track because there are a lot of tangents in this thread.

#1 - Don't get hung up on the fact that it's a C-172P, I need to make a few more for other airplanes on the ramp so aircraft model is irrelevant.

#2 - I know how to make a fuel dip stick so no need to post instructions on how to calibrate one, what materials to use, etc.

#3 - The only difference between putting Usable vs Total Fuel on the stick is the number written next to the lines. So for example, if an aircraft has 13 gallons total per tank but only 12 gallons usable per tank, then the top line indicating FULL on the dip stick would say 13 if I go with Total fuel, and 12 if I go with Usable.

To Clarify - My question is which number, Total or Usable, is better to have on a fuel stick? For example, which one is better for calculating fuel burn? Which fuel number do you guys use for flight planning and should the number on the fuel stick match the calculations on your flight plan, or weight and balance, or does it have no impact? What do most GA aircraft gauges allegedly show (usable I think) and would it be better if that matched the stick? Dipping the fuel and seeing Total, might mean someone makes a mistake and thinks they have more fuel in the tank than they actually do. These are the types of questions I'm trying to weigh the pros and cons of because I've heard arguments that TOTAL is better for accurate and faster planning and calculations but Usable is more relevant and applicable in daily life.
Click to expand...

Unusuable is always the same, and even so, there is no reason I would have know what it is if I know the usable quantity. Including unusable on a dipstick serves literally no purpose.

The fuel gauges on the instrument panel are marked in usable.
 
SONICMASD said:
What do most GA aircraft gauges allegedly show (usable I think) and would it be better if that matched the stick?
Click to expand...

Cessna, at least, specifies that the gauges read zero when the tanks contain only the specified unuseable fuel. That reflects the regulations:

§ 23.1337 Powerplant instruments installation.

Fuel quantity indication. There must be a means to indicate to the flightcrew members the quantity of usable fuel in each tank during flight. An indicator calibrated in appropriate units and clearly marked to indicate those units must be used. In addition: [] Each fuel quantity indicator must be calibrated to read "zero" during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply. . .
 
If you calibrate your fuel stick in total, then dip it in the tank and don't jiggle it around to make sure it's bottomed out, it could read zero. You might think to yourself, "Self, this tank is bone dry so I can add 20 gal (or whatever) into it knowing that 2 gal are unusable and 18 gal are usable. Then you'll wonder why you could only fit 18 or so into it.

If you calibrate your fuel stick in usable, then dip it in the tank and don't jiggle it around to make sure it's bottomed out, it could read <zero. You might think to yourself, "Self, how can this tank be less than empty?" and realize there are 2 explanations; one is that it is bone dry, the other is that you didn't hit the bottom of the tank.
 
Matthew said:
If you calibrate your fuel stick in total, then dip it in the tank and don't jiggle it around to make sure it's bottomed out, it could read zero. You might think to yourself, "Self, this tank is bone dry so I can add 20 gal (or whatever) into it knowing that 2 gal are unusable and 18 gal are usable. Then you'll wonder why you could only fit 18 or so into it.

If you calibrate your fuel stick in usable, then dip it in the tank and don't jiggle it around to make sure it's bottomed out, it could read <zero. You might think to yourself, "Self, how can this tank be less than empty?" and realize there are 2 explanations; one is that it is bone dry, the other is that you didn't hit the bottom of the tank.
Click to expand...

In most tanks you won't even get the dipstick wet with just the unusable fuel in the tank. The wing dihedral and ground attitude usually has the unusable fuel hiding in the inboard rear corner, away from the filler neck.

In the Cessna 180/185 the dipstick won't register anything until the tank is nearing a quarter full. I made special dipsticks for those, T-shaped, with the T-bar that sat on the top of the filler neck and the dip was a curved thing, like a banana, to reach toward the back so one could get readings not available with a straight stick. Made them of aluminum and painted them with epoxy zinc chromate primer; shows the fuel level the best. They were also designed to not quite contact the bottom of that fuel bladder; repeated rubbing of that will damage it and it'll leak.
 
I have a couple Fuel hawks.

The 152 version (12 gal tanks) has the zero mark nearly one inch up.

The 172 (26.5? gal tanks) has the zero mark about 1/8" up.
 
Matthew said:
I have a couple Fuel hawks.

The 152 version (12 gal tanks) has the zero mark nearly one inch up.

The 172 (26.5? gal tanks) has the zero mark about 1/8" up.
Click to expand...
Yeah, the 150/152 would be like that. They have 13 gallon wing tanks, of which nearly two gallons is unuseable (3.5 gallons between the two tanks). That's a large proportion of the total fuel, and it's due to the small wing dihedral, a rather flat-bottomed tank, and fairly flat three-point attitude.

The last iterations of the airplanes had an unuseable of 9 pounds (1.5 gallons) instead of 21 lb, and I'd bet it was because they installed two outlets and two fuel lines down the front and rear doorposts instead of the single centered outlet and the line down the rear post only.
 
I apologize but I don’t have time to read the thread. Unusable fuel isn’t your concern. Usable fuel is ALL you need to measure. Set your plane in level flight and drain usable fuel through the strainer. Place back into ramp position. Pitch the goofy “universal” tubes and get a wood paint stir stick. Measure zero fuel and mark if it shows. Add 5 gallons a side and mark your stick. With luck your tanks share marks. Mine have. Add 5 gallons at a time and mark the increments. Now you know what you have relative to when you’ll run out. Maintain a safe margin. Happy flying.
 
^^^

Would setting fuel selector OFF be a good idea too?

I know on our old club 150 that fuel crossfeeding was an issue. Maybe it was because the ramp wasn't level. I remember fueling one side until full, filling the other side, then topping off the first side again.
 
Stewartb said:
I apologize but I don’t have time to read the thread. Unusable fuel isn’t your concern. Usable fuel is ALL you need to measure. Set your plane in level flight and drain usable fuel through the strainer. Place back into ramp position. Pitch the goofy “universal” tubes and get a wood paint stir stick. Measure zero fuel and mark if it shows. Add 5 gallons a side and mark your stick. With luck your tanks share marks. Mine have. Add 5 gallons at a time and mark the increments. Now you know what you have relative to when you’ll run out. Maintain a safe margin. Happy flying.
Click to expand...
Should have read the thread....unuseable fuel is not undrainable fuel...
 
Matthew said:
^^^

Would setting fuel selector OFF be a good idea too?

I know on our old club 150 that fuel crossfeeding was an issue. Maybe it was because the ramp wasn't level. I remember fueling one side until full, filling the other side, then topping off the first side again.
Click to expand...


Shutting off a 150's valve won't stop the crossfeeding. The 150's tanks feed aluminum lines that tee together just upstream of the shutoff valve, and the valve simply turns the fuel on or off. With it off, the fuel will still crossfeed through the tee.

A 172 or higher model has a selector that shuts off all lines in the off position, and it won't crossfeed. Even if the selector is on left or right it can't crossfeed.

The injected Cessnas have a left-both-right valve, without the off position. Got to put it in left or right to prevent crossfeeding. There's a separate fuel shutoff valve, operated by a push-pull cable. It's because the injection systems have a header tank fed by the selector, and if the selector valve had the off position you'd have two problems: First, if you had an engine fire you couldn't stop the header tank from feeding it, and second, you could actually get off the ground with the selector valve in the off position, using just the gallon or so in the header. Then the engine would quit. So the shutoff is at the outlet of the header instead of at the selector.
 
Last edited:
I have digital fuel qty gauges that are calibrated to each gallon and an FS-450 fuel monitor. The one fuel tool I trust most is my dip stick. If you've ever been low enough on fuel that you rock your wings to get every drop as you cross a few miles of water to get to the runway? You tend to pay more attention to small details like accuracy of your fuel qty on board.
 
Stewartb said:
I have digital fuel qty gauges that are calibrated to each gallon and an FS-450 fuel monitor. The one fuel tool I trust most is my dip stick. If you've ever been low enough on fuel that you rock your wings to get every drop as you cross a few miles of water to get to the runway? You tend to pay more attention to small details like accuracy of your fuel qty on board.
Click to expand...

That's why the FAA defined unuseable fuel in FAR 23. What you can drain out through the strainer is a lot more than what will remain without reaching the tank outlets in a steep Vx climb or power-off, full-flap approach. I have drained fuel that way, in the process of draining the system, as I noted in posts in this thread, and it leaves much less than unusable. And I have seen two deadstick landings in 150s in the flight school due to someone (not me) calibrating sticks in your fashion. The unuseable fuel that should have been on board would have been more than the equivalent of the 30-minute VFR reserve. It could have been a fatal mistake.

The FAA also defined the empty weight as including the unuseable fuel as defined by their regs. That way, with a properly calibrated dispick, the pilot need not worry about unusable fuel at all. The gauge is to read zero when unuseable level is reached, too. It's all in FAR 23.

Most of those regulations are written in someone else's blood.
 
The Sport has a built in level indicator. It's a tab in the tank. Bottom of tab is 15 gal, slot in the tab is 20 gal. Tank holds 30 gal. I never TO with the fuel level below the bottom of the tabs. That's 30 gal total. Fuel burn is 8.5 gal/hr and I plan for 10 gal/hr. Haven't run out of fuel in 24 years flying...:)
 
Dan Thomas said:
That's why the FAA defined unuseable fuel in FAR 23. What you can drain out through the strainer is a lot more than what will remain without reaching the tank outlets in a steep Vx climb or power-off, full-flap approach. I have drained fuel that way, in the process of draining the system, as I noted in posts in this thread, and it leaves much less than unusable. And I have seen two deadstick landings in 150s in the flight school due to someone (not me) calibrating sticks in your fashion. The unuseable fuel that should have been on board would have been more than the equivalent of the 30-minute VFR reserve. It could have been a fatal mistake.

The FAA also defined the empty weight as including the unuseable fuel as defined by their regs. That way, with a properly calibrated dispick, the pilot need not worry about unusable fuel at all. The gauge is to read zero when unuseable level is reached, too. It's all in FAR 23.

Most of those regulations are written in someone else's blood.
Click to expand...
Are you a pilot?
 
Stewartb said:
Are you a pilot?
Click to expand...
Canadian commercial license. Before they expired, I held IFR and instructor ratings. I am a Canadian Aircraft Maintenance Engineer (US A&P/IA equivalent).
 
You must log in or register to reply here.
Back
Top