50 Gallons or 64 Gallons

[gwav8or]

So my F has the 64 gallon tanks. The owner I bought it from said he never filled more than 50 gallons. The CFI that helped with my transition also owns an F with 64 gallons. He said he never fills more than 50 also.

 

So is there a reason not to fill more than 50 other than weight?

 

 

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[EricJ]

6 minutes ago, gwav8or said:

So my F has the 64 gallon tanks. The owner I bought it from said he never filled more than 50 gallons. The CFI that helped with my transition also owns an F with 64 gallons. He said he never fills more than 50 also.

 

So is there a reason not to fill more than 50 other than weight?

Not that I can think of, unless they have leaks above that level. 

[KSMooniac]

50 gallons will get you very far away, but reduces performance with the extra 84 lbs is weight. I never fill all the way up either unless gas is cheap, and if I don't have a full cabin. I also have a fuel totalizer and am comfortable taking off with 32 gallons, or 44, or whatever I have on board at the time. Some people can't graduate past always filing up like with an old rental flight school plane with bad instruments.

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[Shadrach]

I rarely fill the tanks on my F.  I almost never need 6hrs of endurance, but I might need the payload in the cabin. 50 gals will take me nearly 600nm with reserves and allow for >700lbs in the cockpit.

[Utah20Gflyer]

It might be because it's much easier to add fuel than remove it if it turns out you need extra weight capacity on your next flight.  

[DCarlton]

I rarely fill mine to the top but sometimes I’ll leave it down about two inches from the top if fuel is cheap.  About the middle of the tabs.  Longest I’ve ever flown was 4.5 hours.  

[ArtVandelay]

Shorting your fuel stops means making more of them. Refilling isn’t that enjoyable to me to want to do it more often.

[Pinecone]

Hmm, several sources state that full takes helps keep the tank sealant moist and sealing.

I may not fill both tanks, but I tend to fill one, alternately.

[A64Pilot]

26 minutes ago, Pinecone said:

Hmm, several sources state that full takes helps keep the tank sealant moist and sealing.

I have bladders and keep them filled at all times for the reason you state, bladders that are kept less than full, the top of the bladder deteriorates, the ones that do the worst are kept tied down and the theory is the heat of the sun daily ages them faster. That’s a pretty well established fact as so many bladder repairs have seriously deteriorated tops.

But if the same is true of wet winged aircraft that would mean the leaks occur more often on the top of the wing. I have a lot of maintenance experience with wet winged crop dusters, except for ferry flights they never top off, average one installs a center point refueling system and takes a partial load each time they fill the hopper as they are very weight constrained.

Those are turbines so a different fuel and that may be why, but the majority of their fuel leaks occur at the main or rear spar,  leaks on the upper surface are rare

 

[A64Pilot]

As I stated I keep my tanks filled because I have bladders, but I maintain a properly designed airplane can fill its tanks, or fill its seats, but not both without being overgross.

If you have a flight that comes up to carry four adults and some baggage, it’s tough to defuel, so you either don’t go or you go overgross.

If you keep your tanks partially full, and that flight comes up, no problem, and if a long flight comes up with just you or one other, then no problem, just refuel before you go.

[carusoam]

Welcome to the Mooney world…

It is full of options…

You are PIC… You have the option to…

1) Fill the seats…

2) Fill the tanks…

3) Fill some seats and some tanks….

4) But, you probably can’t fill all the seats, and all the tanks…. Unless you carry some small people…. Your choice 

5) Keeping tanks full…. Sealants don’t actually dry out… nor do bladders….   But, if you ever measure the temperature of a piece of metal sitting out in the sun on a hot day…. You will wish you left the tanks near full on those days….
 

6) If you extend this question to Long Body owners… they have the option to have up to 130 gallons on board… and tools to accurately partial fill the tanks…  time to calibrate a fuel stick!

7) Weight has a penalty… time to fire up that WnB app to make sure it is working…

8) Have you done the calculations for T/O distance? This is where the weight penalty usually gets discussed…

9) Know there are times to not have too much fuel on board…

10) Did we discuss DA lately? It’s still warm out… density altitude is important…. It affects power and lift in a negative way…

11) For comparison… the M20C got 52gal usable… older ones were slightly less…. At 10gph that is a lot of flight time…

Go Mooney!

PP thoughts only, not a CFI…

Best regards,

-a-

[AIREMATT]

On 9/22/2022 at 12:09 AM, ArtVandelay said:

Shorting your fuel stops means making more of them. Refilling isn’t that enjoyable to me to want to do it more often.

Need for Emptying the bladder usually happens before the need to use over 5 hours of fuel in the tanks

[MikeOH]

21 hours ago, AIREMATT said:

Need for Emptying the bladder usually happens before the need to use over 5 hours of fuel in the tanks

While true, there's nothing like needing another hour of fuel and NOT having it to soil your shorts!

[Shadrach]

On 9/22/2022 at 7:58 AM, Pinecone said:

Hmm, several sources state that full takes helps keep the tank sealant moist and sealing.

I may not fill both tanks, but I tend to fill one, alternately.

I don’t think keeping full tanks keep things moist so much as it stops the sealant from oxidizing whenever the tanks are full.  I also think that planes that live outside are affected by the heat of the sun on the top of the wing. I would guess that dark colored wings and wing walk areas might see wing top surface temps upwards of 120° In parts of the country. Heat accelerates chemical reactions. Dry, hot, sealant likely deteriorates more rapidly.

[Pinecone]

Very possibly.