how much confidence do you have in fuel gauges?

Discussion in 'Hangar Talk' started by readytocopy995, Jul 30, 2022.

  1. Dan Thomas

    Dan Thomas Final Approach

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    Fuel gauges fit into the same category as any other instrument. When you're IFR in IMC, you use the six-pack to determine what the attitude, heading, speed and vertical attributes are. If one of the instruments fails, you use the others to put together the info you need. It's one reason it takes a lot of dual to get that IFR rating.

    If a fuel gauge fails or becomes suspect, your watch and the fuel burns from the POH are the backup. This adds work, so we want those gauges accurate, accurate like they were when the airplane was new.

    If the oil pressure gauge fails, we can use oil and cylinder head temperatures to confirm whether or not the pressure is really gone.

    If the oil temp gauge fails, we can watch the pressure and see if it falls, as it will if the oil heats up.

    We make sure we have accurate oil pressure and temperature gauges. But many don't much care if the fuel gauges are way off. Why is that?
     
  2. SkyChaser

    SkyChaser Cleared for Takeoff

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    If you're flying around with no idea when you're stopping for fuel, I see why you'd start looking at half tanks. Do you also flight plan cross country flights this way? Genuinely curious.
     
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  3. readytocopy995

    readytocopy995 Pre-Flight

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    this doesn't make much sense as a strategy. perhaps in whatever you're flying you have enough fuel and load to do it this way but in many airplanes you need to trade some fuel for load

    in the example airplane for instance with four people you can't even takeoff with more than half tanks. the plane is capable of flying over 2.5 hours. are you saying that's not enough fuel for you?
     
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  4. Maxnr

    Maxnr Line Up and Wait

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  5. Rgbeard

    Rgbeard En-Route

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    My plan on my plane, for 4hr legs goes like this:

    Begin tanks full. 47 L & 47 R, usable fuel.

    Takeoff and climb is in the low 20s/hr fuel consumption, and I call 45 mins of this a "fuel hour"
    Cruise is around 16/hr

    0:00-0:45 - Begin on initial tank. Let's say "LEFT". Appx 16gal depleted.
    0:45-2:45 - 32 gal used from RT
    2:45-3:45 - another 16 gal from LT. At this point, appx 15 remains per-side, 30 total.
    I'm beginning my landing solution - whatever it is - and I have just over 2hr remaining, if I pulled back to 55% power.

    I've got lots of fuel receipts showing low-70s gallons purchased using this method, and it "jives" with the numbers I expected to see in the tank.

    All the time, After the first two hours of flight, I can consult the wing mounted round fuel gauges, and be sure I'm getting my expected fuel rates. (no surprises).
     
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  6. mryan75

    mryan75 Pattern Altitude

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    Awesome.
     
  7. mryan75

    mryan75 Pattern Altitude

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    I knew before posting what I did that we would wind up exactly here. Every statement of a position has to be the length of an encyclopedia entry nowadays, with every possible variation covered, because no matter what you say, someone is going to come up with a hypothetical to prove you wrong or make your statement seem absurd. It's just the way of the world. I mean, one response I got was about how this wouldn't make sense for a 787. I don't even know what to say to that.

    I don't trust fuel gauges in the planes I fly. I am very conservative on fueling. That's my position.
     
  8. Timbeck2

    Timbeck2 Final Approach

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    welcome to the internet my friend ;)
     
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  9. Tarheelpilot

    Tarheelpilot Final Approach PoA Supporter

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    Well you also come across like you are not interested in listening to meaningful input. Hence my concise answer to your question.

    Yes. The 787 response was absurd.

    No. I don’t think you’ll listen to any input here. You’ve put us all into the same category as the 787 comment.

    Just in case you are receptive: Get your fuel gauges fixed. They should be reliable and trustworthy.
     
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  10. Half Fast

    Half Fast Final Approach

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    I paid about $2k to get my fuel gauges fixed a year ago. At least they work now, but they still aren’t particularly accurate nor trustworthy. I trust them for leak detection but trust my clock for fuel remaining.
     
  11. Pinecone

    Pinecone Pre-takeoff checklist

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    What aircraft do you fly???

    Again, I am not landing after burning 50 gallons of a 100 gallon system, unless I need a toilet or get hnugry.
     
  12. SkyChaser

    SkyChaser Cleared for Takeoff

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    I plan out how much fuel I should be burning, and watch both my watch and the gauges. I trust whichever shows a lower level of fuel at any given time. My desired reserve depends on where I am and where I'm flying.
     
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  13. mryan75

    mryan75 Pattern Altitude

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    That's great, I'm glad you have a plan and solution that works for you.
     
  14. Pinecone

    Pinecone Pre-takeoff checklist

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    Interestingly, I ran across the page from the parts manual on Mooney Space, and Mooneys seem to have only one fuel port.

    Multiple ports can work fine on gravity systems, but may be problematic with a fuel pump drawing fuel UP. Same way low wing planes don't have a Both selection for the fuel tanks.
     
  15. Tarheelpilot

    Tarheelpilot Final Approach PoA Supporter

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    Nothing you are saying is contrary to my posts. If you didn’t trust your gauges you wouldn’t use them for leak detection.
    I use a flight timer as well.
     
  16. mryan75

    mryan75 Pattern Altitude

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    Well here's the thing, nothing I have said should give the impression that I'm not interested in feedback. Then I ask for some and I don't get an answer. So where does that leave me? Ya know? Not really sure what's going on here to be honest. Someone asked how much we trust fuel gauges. In my case the answer is "not much". I have a loose rule that I fly by, which is that when my gauges show about half full, I'm thinking about more fuel. And in my case it "don't" really matter that much. Guess why? I can't fly more than 2-2.5 hours without having to take a ****. Besides, going up and coming down is the fun part. Secondly, when you're cruising at 115 knots, what blessed difference does it make? Not much. I'm not making it to Florida in one leg (from my home base in NY). I know how much my plane burns; I keep meticulous track of it. But I'm simply not going to try going super lean at 55% power so I can fly for 5.5 hours before I land. I see no fun in that, I see no point in that. Do you know how much time adding one stop to a 1,000-nm trip makes in my plane, so I can keep my legs a bit shorter? Not a whole helluva lot.

    So there ya go. My answer was and is, when I get near half tanks, I am thinking about more fuel. And as per usual most people here disagree with me. All good. I knew it before I wrote the words and it's fine. My last point that I will repeat: one pilot, ahem, "pilot", a week runs out fuel in this country. One a week. And it's been that way for decades. And rather than the discussion be, how can we be a bit more conservative and avoid this needless nonsense, the question is, "how far can we push it?" Well, the answer is you can push it until you run out of fuel. Be my guest.

    So there you go. Far be it from me to ask for a reasonable response to a genuine question.
     
  17. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    One very good way to avoid running out of fuel is to have fuel gauges that work, per airworthiness requirements, and the pilot actually understand how they work so they can be trusted. Proper planning and timing are important, but they’re only additional tools. take away any one, and you’re eliminating tools available to prevent fuel starvation or fuel exhaustion.
     
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  18. mryan75

    mryan75 Pattern Altitude

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    My fuel gauges work per airworthiness requirements, like everything else on my airplane.
     
  19. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    But…
    So you are eliminating one of the tools available.
     
  20. Tarheelpilot

    Tarheelpilot Final Approach PoA Supporter

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    You’re still not getting it. I’m not advocating for “pushing it” I’m advocating for flying properly maintained aircraft and making active and appropriate decisions about fuel management for each flight. Flying until you figure you’re around half tanks you start looking for gas is not a plan. It’s a good way to screw yourself.

    But you do you. As you said. As soon as you posted you knew someone would have a problem with it and you’ve listened about as much as would be expected.
     
  21. CaptainXap

    CaptainXap Pre-Flight

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    I listened to a podcast a few months back where the host was talking to a pilot from Australia about fuel gauges. In Australia the fuel gauges gave to be calibrated every four years, which means that they're basically pretty accurate all the time. In the US there appears to be no requirement for fuel gauges to be calibrated, so it's not something that seems to happen very often. And then we moan that the gauges are inaccurate when they've basically been left to drift out of whack for 45 years.
     
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  22. Tom Wells

    Tom Wells Pre-takeoff checklist

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    I fly a "legacy" aircraft ('72) and I share the chronic fear of not wanting to run out of fuel. So I hear ya. When flying I'll take the lower of 2 numbers: what I manually compute the fuel should be based on time/fuel burn, and what the gauges show.
    But if I determine I still have 50% of my fuel remaining, I ain't landing unless there is some other need. I won't fault someone who does, that's their own choice, but that'd lead to an excessive number of stops. But hey, if it works for you, then on the bright side you get to experience a lot more airports.

    Plus, in my plane, full L/R tanks and passengers on a warm day like today means I'm climbing... slowly. Starting with ~1/2 tanks for a reasonably short flight is totally fine and often a deliberate decision.
     
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  23. mryan75

    mryan75 Pattern Altitude

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    There's nothing to listen to. You've gone from one-word answers to insults. You're correct that I'm not getting it because there's nothing to get. What is there to get from "it's not a good plan"? I'm going to really go out on a limb here and assume that you don't think it's a good plan. Which is of no use to me. If you would explain your point of view it would be helpful, but you clearly don't intend to do that. So there ya go.

    It's absolutely hilarious - you say I'm not willing to listen, yet you refuse to give me anything constructive to listen to. So who's the problem here? I made an attempt to explain myself, for all the good I knew it would do me.
     
  24. mryan75

    mryan75 Pattern Altitude

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    Nope.
     
  25. Daleandee

    Daleandee En-Route

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  26. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    So…
    Then
    Seems a lot like not being willing to listen.
     
  27. Dan Thomas

    Dan Thomas Final Approach

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    Landing for fuel just because the gauges read half is fine. Do it. But stop telling us that this is a wise and practical thing to do. It is not. Nowhere in the training syllabi or textbooks or FARs will you find such advice. You do in only because your old instructor told you to, and he did that because the gauges in the airplanes he flew were so out of whack they wouldn't have been anywhere near legal.

    Advice intended to keep one flying unairworthy airplanes is not good advice. If I find a cracked spar in a wing, I don't tell the owner to fly real careful and gently and not pull any G's. If I find a frayed control cable, I don't tell him to think about replacing it next year. If I find a cracked muffler, I don't tell him to get a CO monitor. Nope, I tell him not to fly it at all until it's fixed.

    The problem is that defective fuel gauges won't cause the airplane to fall apart or catch fire or go out of control in the air, so owners get complacent about them until one day when they really wish they had gotten them fixed. Here in Canada (and Alaska) there are places where there are some very long distances between airports, and you'd better have your fuel planning and engine management techniques down pat or you'll run out of fuel before you get there. If you have to land at half tanks, you ain't going. You're sticking close to home. Everybody else will go and have fun, though.
     
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  28. mondtster

    mondtster En-Route

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    Not only are the airports farther apart, many remote airports don’t have fuel at them unless you bring it with you or have it shipped in. Based on some of the assumptions being made, It is fairly apparent that some respondents to this thread haven’t strayed too far from civilization in an airplane, despite it being one of the best tools for it.
     
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  29. MooneyDriver78

    MooneyDriver78 En-Route

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    Defective (not working at all) is one thing, not very accurate is another.
    My fuel gauges work, they’re not very accurate (~10% off at times). I wont use them to calculate fuel left to fly down to last gallon, but I do have confidence enough if I saw one dropping I would land to check for a fuel leak.
     
  30. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    Define “10% off at times.” ;)

    note that the certification reg says you need to be able to determine how much fuel is in the tanks, not that the 1/2 mark = 1/2 full.
     
  31. MooneyDriver78

    MooneyDriver78 En-Route

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    Just what it says, my tanks aren’t rectangular, they’re an odd shape, least accurate at the top where the tank is widest.
    Certification reg above does not say how accurate, down to fraction of an ounce? Within a gallon?
     
  32. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    It doesn’t say they need to be accurate (except at empty)…it says you need to be able to determine he amount of fuel that’s in the airplane.
     
  33. Bell206

    Bell206 Final Approach

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    The hard calibration point for both CAR 3 and Part 23 aircraft is zero at unusable fuel in level flight. For the most part, the rest of the fuel quantity reading accuracy falls under industry or OEM standards. But in my experience, odds are if the quantity readings are off substantially in the mid-range the zero point is usually off as well.
     
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  34. Dan Thomas

    Dan Thomas Final Approach

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    They should give a good idea. 10% is a fair idea. That's two gallons in a 20-gallon tank.

    Fuel gauging by a float on an arm has serious limitations. The float will hit its lower stop, or the bottom of the tank, while there is still fuel in the tank, often more than useable fuel. It's not good to have the float tapping the tank, so the stop is set so it can't, and that leaves even more fuel remaining when the gauge stops moving, and that's usually a bit below the E. Same with the top of the tank: the float will hit its upper stop, but more fuel can still be added but the gauge won't move any higher. You could easily have a 10% error at either end of the scale. Can't get around that.

    Then there are the factors I mentioned earlier, the biggest being shallow tanks, made that way so they'll fit in the wing. The fuel sloshes around depending on pitch attitude and coordination. The ideal spot for the sender would be the center of the tank, but that doesn't work if there's any dihedral on the wings, which there always is, and there's a lot more in a low-wing airplane. So the sender has to go into the inboard end of the tank so the unusable fuel can be gauged as per FARs. Now we have a setup where the gauge handles the lower fuel levels OK but toward Full, not so much. That float is against its upper stop long before the tank is actually full.

    There are few solutions. Big aircraft use multiple capacitance probes, with the results summed, to get accurate fuel levels. Those affairs can measure the whole vertical column, from full to empty. Placing several of them in various areas of the tank means that as one reads low as fuel shifts away from it, another reads higher because the fuel shifted toward it, and the sum is the same. Nice, but more complex and a lot more expensive.

    The beef is not with gauges that are off 10%. The argument is against gauges that can't even do that, some of them off so far you have to land for fuel when the gauge reads half full. That's just rotten maintenance.
     
  35. Dan Thomas

    Dan Thomas Final Approach

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    This is a typical, simple fuel gauge circuit:

    upload_2022-8-4_15-10-11.jpeg

    It's designed so that varying supply voltage won't change the reading.

    On the right we have the fuel sender with its float on the fuel and working a rheostat (variable resistor). That rheostat works an electromagnet that raises the fuel gauge needle. When the tank is full, resistance is minimum and max current flows and pulls the gauge needle up to full.

    One the left is a reference resistor. Its lower end is grounded. It feeds the other electromagnet, the one that pulls the needle toward empty. When the tank is half-full, the two resistances are the same so that the electromagnets have equal pull, so the needle centers. When the tank is empty, the sender's rheostat is at max resistance, the tank-side electromagnet gets little current, so it has little pull, and the left-side one overpowers it and pulls the needle to Empty.

    The sender is the biggest problem. It wears out. It gets corroded. It wiring has crimp terminals that get corroded. The grounding of the sender to the tank gets compromised by dirt and residue from fuel leakage, and its ground straps get messed up by gasket sealant or whatever the mechanic uses on it. The tank's ground straps are often oxidized or loose or even broken.

    The wire connectors between the wing and fuselage get dirty or corroded. Inside the airplane, the gauge grounding at the panel can get compromised by corrosion. Inside the gauge itself, that reference resistor can fail, and the ground connections can get corroded. The needle mechanism gets old and sticky.

    New senders are available for many older airplanes. There are outfits that rebuild them. New gauges are a lot more expensive, maybe not even available, but there are modern STC'd substitutes. I bet you'll never find a new OEM gauge for your '65 Chevy, either, and maybe you won't even find an aftermarket solution. At least we have that for airplanes.
     
  36. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    What if your certificates airplane fuel gauge and sender are from a ‘38 Chevy?
     
  37. readytocopy995

    readytocopy995 Pre-Flight

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    i feel like you're just admitting to yourself that it's not a reasoned position. do you trust your gauges and your flight timing or not? you're scared to forget to fuel up or stop, i guess, so you just always make sure you have way more than you'll ever need. no offense, but i feel this mentality has probably led to more people having an "oh ****" moment with regards to fuel than people who try to understand their equipment and its limits

    hey man do whatever you want, be as conservative as you want, but i don't think that 'saves' you from accidents or misfortune. i find it odd how obsessed you make it sound like you are about your airplanes fuel burn, only to load it up with 5.5 hours of fuel for a 2 hour trip. i don't know the data, but it wouldn't surprise me if more people get into trouble with having more weight and worse climb than they need than who run out of gas

    yep. and to be clear i'm not trying to "push it" either. i just want to know, what are my chances of having fuel starvation with x fuel so that i can make sure i always have a decent reserve on top of that point.
     
  38. Dan Thomas

    Dan Thomas Final Approach

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    Then the airplane will be from that era as well. Pretty tough to find stuff like that. In Canada we have the Owner-Maintenance category that allows certain mods, and fuel gauge updating would be within the limits. TC knows that parts for old airplanes are hard to find, and they'd rather you have something that works properly rather than something that keeps getting patched up and is not reliable.

    Aircraft Spruce has gauges that are TSO'd but not STC'd for installation. You have the 337 process for field approval for such stuff. We have a Major Modification process to do the same thing.
     
  39. Pinecone

    Pinecone Pre-takeoff checklist

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    It also depends on the circumstances.

    Do you own or fly that aircraft on a regular basis? If so, are the gauges consistent? As in, if they read half, you have about X amount of fuel, whether X or not.

    It a accuracy versus precision situation. Accurate is that 1/2 on the gauge is 1/2 the fuel. Precision is that when the gauge reads 1/2, X amount of fuel remains, every time.

    Accuracy is nice, but precision is more usable. Both is the holy grail.

    If you are flying rentals and different airplanes every time, I would rely on the gauges less.
     
  40. kgruber

    kgruber En-Route

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    Caution is in order. Even my brand new Super Cub had a problem with the sight fuel gauge. Its little red bobber got stuck on full.