Full Fuel Tanks

[milotron]

Hi, how far do you fill your tanks before they are considered 'full' either by Mooney design or by the gauges? Is it up the bottom of the fuel cap frame? Below the flappy thing?  I cannot get my tanks 'full' per the panels gauges, but the wing gauges always go well past the '30 gal' mark on them.  These are standard tanks on M20K.

It would seem I need to get them calibrated somehow.

Are the wing gauges more reliable than the gauges inside?

 

Thanks,  

 

iain

[gsengle]

Get a totalizer. Your gauges are only required to be accurate at zero. Personally I wouldn't waste money trying to make them more accurate.

 

An upgraded engine analyzer is a must anyway and can add a fuel flow option.

 

For my Ovation, bottom of the filler necks is 89. I find the wing gauges accurate, the panel ones not.

 

 

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[milotron]

Thanks. I do have a totalizer, but still need to know what is left to know the total that I have available after a known quantity is added.  I agree that the wing gaages are more accurate and will estimate remaining using these.  

[gsengle]

Thanks. I do have a totalizer, but still need to know what is left to know the total that I have available after a known quantity is added.  I agree that the wing gaages are more accurate and will estimate remaining using these.  

I've found the wing gauges adequate for this as I usually don't ever land with less than 20gal or take off with less than 30... not sure there is a better solution. My fuel purchases seem to confirm accuracy of both those gauges as well as the totalizer...


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[mooneyspeed]

Out of the 37.8 gallons useable per wing I find that the tank seems to be empty after 35 gallons according to how much I can put back in. I use a FF meter/totalizer and it coincides nicely with what goes back in at the pump.

You just have to track what you burned because those panel gauges aren't great at all. Even after having the senders done.


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[gsengle]

I guess my point is that you know how much you have at full. After that you know what you burned. In that instance you can verify what gauges are accurate when against totalizer and or fuel put back in. You can verify that your totalizer is accurate. And from then on, as long as you don't push fuel reserves, mine is ten a side in the Ovation which is over an hour, the error will always simply be how generous your reserve is not how little fuel I have left. I've confirmed that my wing gauges are very accurate at 10-25 gallons, which helps a lot. Finally I've known people to spend $$$ trying to get their panel fuel guages accurate. They still aren't accurate after spending some real money :/


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[milotron]

22 minutes ago, mooneyspeed said:

Out of the 37.8 gallons useable per wing I find that the tank seems to be empty after 35 gallons according to how much I can put back in. I use a FF meter/totalizer and it coincides nicely with what goes back in at the pump.

You just have to track what you burned because those panel gauges aren't great at all. Even after having the senders done.


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Thanks. Do you fill to the bottom of the fuel cap neck or underside of the flapper to get this quantity? I need to be brave and run one tank empty at some point I suppose.

 

11 minutes ago, gsengle said:

I guess my point is that you know how much you have at full. After that you know what you burned. In that instance you can verify what gauges are accurate when against totalizer and or fuel put back in. You can verify that your totalizer is accurate. And from then on, as long as you don't push fuel reserves, mine is ten a side in the Ovation which is over an hour, the error will always simply be how generous your reserve is not how little fuel I have left. I've confirmed that my wing gauges are very accurate at 10-25 gallons, which helps a lot. Finally I've known people to spend $$$ trying to get their panel fuel guages accurate. They still aren't accurate after spending some real money :/


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This is the method I have been working with, but need to know what a 'full' tank is first. I can't for the life of me get the panel gauges to register full, and the wing gauges only go to 30 gal, then overscale.  I know some aircraft need airspace above the fuel in the tank for expansion and venting, hence my question as to what is considered full. At the flapper there is still air gap to to the top of the wing,  but it takes time to settle out to that level.

[PMcClure]

Per my POH - wing gauges are calibrated for on the ground and panel gauges for in the air. (2002 Ovation). On my plane, full is technical to the bottom of the tab (89.5 gallons) but I can go to the top with some patience (102 gallons). The Ovation has a 5-7 degree ground stance for prop clearance and take off distance improvement. 

Personally, I have found both the ship fuel gauges (panel and wing) dead on accurate and better than the 700 engine monitor. But I trust none of them. 

[carusoam]

Ding Ding Ding we have a winner... 

PMC hit the nail on the head...

The POH has the answer in a couple of places...

The placards on the instrument panel may have a couple of hints as well.

The POH has a filling procedure, that defines when to use which gauges.

 

yes those plastic gauges on the wing are calibrated for filling on level ground.

yes those fancy gauges on the instrument panel are calibrated to be accurate in level flight.

 

A mooney on the ground has about a 4° attitude while on the ground. Not helping filling accuracy any... Long Bodies have a touch more attitude to match their owner's?  

 

Filling the tanks and topping them off requires patience while air is forced out the vent.  Check the vents for big nests... a good mud dauber can block a vent in many parts of the country including NJ.

 

Each Mooney has differences...

1) Some Mooneys got extended tanks with two caps per wing...

2) Some Turbo Mooneys got a flapper valve in the fuel neck....

3) Eagles got the worst fuel neck ever designed by a marketing department. nothing that a good A&P or hangar elf can't fix properly.

4) Improvemets in accuracy come in two forms...

• cleaning and calibrating existing fuel level sensors...
• upgrading to new digital fuel level sensors... @fuellevel see CIES for some cool sensors to go with a cool digital display...

5) Some POH data includes the density of fuel to a few decimal points... helpful for WnB calcs....

6) The challenge I have with the IP fuel gauges, they are not very precise in terms of being able to read gallons still in the tanks.  Not many lines available for interpretation...

 

 

Since running out of energy, prior to arriving at the intended point of landing continues to be an issue for an MSer or known Mooney pilot each year...  It is good to have an accurate fuel level system... and a back-up fuel quantity device of some sort.

+1 FF meter with totalizer...

P0 thoughts only... let your POH be your guide on this one...

How does that sound?

Best regards,

-a-

 

[gsengle]

Yep and I find the wing gauges accurate on the ground and the panel ones inaccurate in flight until approaching zero. I assumed the op had already checked POH-AFM for full fueling instructions....

 

 

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[carusoam]

^^^  Proof that everybody has to test the accuracy of their fuel measuring systems before relying on them to avoid off field landings...

Best regards,

-a-

[milotron]

Yes to all of the above. Gauges in panel are for flight; wing gauges are for ground checks.

Checked POH, but no comment on whether full is what the gauge says; fuel overflowing down the wing or up to the tabs. I have no tabs BTW, just the flappy antisiphon thing

2 hours ago, PMcClure said:

Per my POH - wing gauges are calibrated for on the ground and panel gauges for in the air. (2002 Ovation). On my plane, full is technical to the bottom of the tab (89.5 gallons) but I can go to the top with some patience (102 gallons). The Ovation has a 5-7 degree ground stance for prop clearance and take off distance improvement. 

Personally, I have found both the ship fuel gauges (panel and wing) dead on accurate and better than the 700 engine monitor. But I trust none of them. 

What does the POH say for official fuel capacity for your O? Interesting that you can 'overfill' it.

[gsengle]

Ovations have 89 usable, to bottom of filler necks. Easy to push fuel under to exceed 89 up to supposedly 100gal.


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[PMcClure]

47 minutes ago, milotron said:

Yes to all of the above. Gauges in panel are for flight; wing gauges are for ground checks.

Checked POH, but no comment on whether full is what the gauge says; fuel overflowing down the wing or up to the tabs. I have no tabs BTW, just the flappy antisiphon thing

What does the POH say for official fuel capacity for your O? Interesting that you can 'overfill' it.

No comment. 

[Yooper Rocketman]

I have a K model with the anti-siphon necks.  I routinely get 4 more gallons per side after reaching the bottom of the filler neck by filling slowly and letting the air bleed out of the tank through the vent.  On long cross country flights those 8 gallons are a big plus.  I've never considered it full unless filled so the cap just clears the fuel in the tank when installed.

Tom

[mooneyspeed]

This is the method I have been working with, but need to know what a 'full' tank is first. I can't for the life of me get the panel gauges to register full, and the wing gauges only go to 30 gal, then overscale.  I know some aircraft need airspace above the fuel in the tank for expansion and venting, hence my question as to what is considered full. At the flapper there is still air gap to to the top of the wing,  but it takes time to settle out to that level.

I fill to the bottom of the neck, so there is some fuel on that flapper. Give the wing a nudge let it move some air out and continue. Then I go to the next wing do the same thing and by the time that's done I can come back to the previous wing and maybe get 1 more gallon into it, with patience. Repeat for wing 2.


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[Guest]

6 hours ago, milotron said:

Hi, how far do you fill your tanks before they are considered 'full' either by Mooney design or by the gauges? Is it up the bottom of the fuel cap frame? Below the flappy thing?  I cannot get my tanks 'full' per the panels gauges, but the wing gauges always go well past the '30 gal' mark on them.  These are standard tanks on M20K.

It would seem I need to get them calibrated somehow.

Are the wing gauges more reliable than the gauges inside?

 

Thanks,  

 

iain

Iain,

Here is the procedure,

 

[201er]

Fly a tank dry, fill it, read the pump. Choose your own "top off" point and you'll know how much you have other times.

[Bob - S50]

What 201er said.  Or technically, fly it almost dry.  Drain the rest through the gascolator and sump and put it in the other wing.  Next, add the unusable fuel.  THEN fill it and see how much fuel it takes to fill to the point that YOU want to consider full.  Personally, I fill to the bottom of the filler cap seat.

However, you can't always count on a totalizer.  The transducer could malfunction and show less burn than actual.  You could develop a leak prior to the transducer.  You could vent fuel overboard and not notice.  Lots of ways to use/lose fuel that does not show up on a totalizer.

That's why we put in the Cies floats and digital gauge.  I can now compare my totalizer with the fuel gauge.  If they agree, I'm happy.  If they don't, I can land and find out why before something worse happens.  So far, both have stayed within a gallon of the other.

[201er]

24 minutes ago, Bob - S50 said:

What 201er said.  Or technically, fly it almost dry.  Drain the rest through the gascolator and sump and put it in the other wing.  Next, add the unusable fuel.  

I agree with all but this. Yes, you want to exactly run it dry and you don't want to sump a drop after. We don't care about how much unusable fuel it can take. We don't care how much can be sumped out after it runs dry. Running it dry in level cruise flight, no more no less, will allow you to find out exactly how much usable fuel you get when you fill to your chosen top off point.

Edited July 15, 2017 by 201er

[ragedracer1977]

I ran my first tank dry today.  Yes, on purpose.  Fuel capacity is listed at 24g.  It took 24.1g to fill it to the brim.  Panel gauge is off a tick.  It read just about 1/4 of the way up between 0 and 36lbs.

[Guest]

20 hours ago, 201er said:

I agree with all but this. Yes, you want to exactly run it dry and you don't want to sump a drop after. We don't care about how much unusable fuel it can take. We don't care how much can be sumped out after it runs dry. Running it dry in level cruise flight, no more no less, will allow you to find out exactly how much usable fuel you get when you fill to your chosen top off point.

The fuel pick up isn't in the very bottom of the tank.  When the engine quits due to the fuel tank being empty, there will still be some small amount of "unusable" fuel which can be drained from the tank drain.  

Clarence

[peevee]

1 hour ago, M20Doc said:

The fuel pick up isn't in the very bottom of the tank.  When the engine quits due to the fuel tank being empty, there will still be some small amount of "unusable" fuel which can be drained from the tank drain.  

Clarence

I don't care how much unusuable fuel I'm carrying. I want the stick to tell me the useable. I can add the unusuable back in for w&b calcs.

[201er]

2 hours ago, M20Doc said:

The fuel pick up isn't in the very bottom of the tank.  When the engine quits due to the fuel tank being empty, there will still be some small amount of "unusable" fuel which can be drained from the tank drain.  

Clarence

Unusable fuel is about as useful to me as the length of the crossing runway at the airport I took off from.

[Bob - S50]

Just now, 201er said:

Unusable fuel is about as useful to me as the length of the crossing runway at the airport I took off from.

Unusable fuel is not some arbitrary number.  The FAA specifies certain conditions under which fuel must still be supplied to the engine.  The manufacturer then tests to determine how much fuel must still be in the tank to meet those conditions.

It is entirely possible, and probable, that the engine will continue to run beyond that point if you are in level cruise in smooth air.  Under other conditions such as climb, descent, or turbulence, that might not be the case.

While it is somewhat comforting to know that the engine may keep running in cruise for a few minutes after my gauge reads empty, there is no way I want to plan on having that fuel available.  I would rather have one gallon more available than I thought rather than one gallon less.