Fuel levels for tank sealant

[VetRepp]

This may be a re-hash of an old topic. I apologize if it's old stuff, but ...

 

I used to always keep enough fuel in my tanks, so that 4 average people could get in and take-off without being over max gross weight, should we need to.

Lately my homebase airport has cheap gas every 2nd Saturday of the month - as a promotion that has stuck, so I'll let my tanks get as low as safely possible (close to that day) then fill up to tops- which saves @ $70, but I've recently heard it's best to keep tanks fairly full to keep sealant wet and last longer. And now I'm wondering if keeping tanks low for up a week will have a negative effect on the tank sealant or future leaking.

 

Anyone have any thoughts on how full the tanks should be when not in use (for sealant or any other reason) ?

 

Thanks

Roger

 

[Jeev]

I always top off my tanks after a flight but I rarely fly with more than just my finance and I.  I have also heard of the sealant drying out but don't have any evidence that it is true, my right tank needed a reseal after 10 years and my left is still going strong.  Someone from Wilmar could probably give an expert opinion on this.

[Piloto]

If you keep your plane in a hangar it makes no difference if full or empty. However if the plane is tied down exposed to the sun the temperature inside the wing will raise well beyond ambient temperature, it could easily reach 160F. Just like fabric on the seats or rubber inside the cabin, the high temperatures causes molecular breakdown (cracks) that causes the sealant to crack and leak. To lower the temperature on the sealant it is recommended to at least leave the tank half full whenever exposed to high temperature environment for a long time.

 

José 

[carusoam]

Polymers hate high temperatures, UV exposure, and oxidation...

Drying out... Is probably an oversimplification. But, it is easy to explain and the advice really works...

Keeping tanks filled, really keeps temperatures lowered. As José eloquently states above...

Lowered temperatures maintains the health of the sealant.

If discounted fuel was available on Saturdays, I would be fully depleted Friday night and stay parked indoors until the fuel truck arrives.

Engineers love this type of challenge.

Just don't run out a few miles short hoping to save the last few bucks...

Engineers like to do it with precision... When they run out, it's only by a few drops???

Realistically, if the sealant absorbed fuel, there would be a slew of additional challenges beyond it drying out...

It would swell, it would flow and it would not really work well as a sealant. fuel would simply pass through it slowly...

I'm a polymers guy, not a mechanic...

Best regards,

-a-

[cbarry]

We could pay $1.00 more per gallon than pilots of other makes and still be considered more efficient.

[VetRepp]

Thanks to all for the quick responses.

Now I understand,  It's not the Drying out that causes the cracks or leaks - it is a sustained Temperature problem; and the fuel is helping by acting as coolant not a hydrator ?

(Fortunately I'm always hangared at a California beach airport where the temp is rarely below 40F or above 80F)

So the consensus is to keep saving the 15-20% on the Cheap fuel Saturday and be even that much more efficient than those other poor pilots.

 

Thanks Again

 Roger

[sleepingsquirrel]

Thanks to all for the quick responses.

So the consensus is to keep saving the 15-20% on the Cheap fuel Saturday and be even that much more efficient than those other poor pilots.

 

Thanks Again

 Roger

 I was reading on a Comanche forum that they had decided the way to find the Comanche pilots at some big aviation shindig was to epoxy a nickel to the hangar floor. It then dawned on them that they would then have to find a way to distinguish the Comanche pilots from the Mooney pilots.

I think  the distinction was if the nickel disappeared.

[VetRepp]

Distinguishing the Mooney Pilot (from the Comanche - or any other) would be easy, They would be the ones getting there much faster, in style, and with a big smile on their face.

 

[Guest]

Distinguishing the Mooney Pilot (from the Comanche - or any other) would be easy, They would be the ones getting there much faster, in style, and with a big smile on their face.

While I love Mooney's, I arrive at 185-190KTAS with a useful load of 1500 pounds and can do that from a 2600 foot grass strip. No Mooney I know of can do that. Oh yeah, it's a Comanche!

Clarence

[sleepingsquirrel]

While I love Mooney's, I arrive at 185-190KTAS with a useful load of 1500 pounds and can do that from a 2600 foot grass strip. No Mooney I know of can do that. Oh yeah, it's a Comanche!

Clarence

Can you do that on 10 GPH?

[chrisk]

Thanks to all for the quick responses.

Now I understand,  It's not the Drying out that causes the cracks or leaks - it is a sustained Temperature problem; and the fuel is helping by acting as coolant not a hydrator ?

(Fortunately I'm always hangared at a California beach airport where the temp is rarely below 40F or above 80F)

So the consensus is to keep saving the 15-20% on the Cheap fuel Saturday and be even that much more efficient than those other poor pilots.

 

Thanks Again

 Roger

 

While fuel does not "hydrate" the sealant, it probably does provide some oxidation protection.    Also from the stories I have heard, heat is the major component of sealant problems.  --Anyway, if your in a hanger, I would not worry about it.   Just don't run out of fuel trying to save a little on fuel.  There was a recent example where this appears to have happened.

[VetRepp]

I know 'hydrate' wasn't PC (...proper chemistry ),  but I couldn't think of the right term.

Anyway thanks ChrisK for the concern, I do always keep enough fuel for at a minimum of 1 hr flying, In fact the most I've ever put in was @ 80 gal (102 gal tanks) But still at  $0.75 - $1 less per gal on cheap Sat - it adds up.

[ArtVandelay]

On a related note, I been told keeping tanks unfilled helps prolong the life of the landing bungees.

Not sure if a couple of hundred pounds makes a difference.

[Guest]

Can you do that on 10 GPH?

10 GPH is a number to pass through while accelerating to 190KTAS, no matter what airframe.

Clarence

[sleepingsquirrel]

10 GPH is a number to pass through while accelerating to 190KTAS, no matter what airframe.

Clarence

Yes, that's how I don't mistake my M20 B for a Rocket or  a Comanche. 

[scottfromiowa]

10 GPH is a number to pass through while accelerating to 190KTAS, no matter what airframe.

Clarence

Good one Squirrel

[jlunseth]

I have heard and read the arguments on both sides of this issue.  I had my tanks resealed at Willmar five years ago.  My practice has been to leave the tanks in whatever state they were in when I ended the last flight, and fill up just before the next flight.  As a general rule, that means they are always left only partly full.  I do that on the theory it reduces to weight load, and also reduces pressure from expansion, and if there is any need for keeping the sealand "wetted," the vapor in the tanks probably does an adequate job of that. 

 

I did a program here in Minn. a couple of years ago that involved landing at all the airfields in the state, which included many short strip landings, some landings on unfamiliar and poorly lit fields at night (which I won't be repeating) and around 40 grass field landings.  Then I prepare for and flew my commercial checkride in the Mooney, and the prep involved not just short field landings but the infamous power off 180 which I practiced quite alot.  My point is that I have not exactly been kind to the aircraft in terms of landing shock force.  I have logged over a thousand landings in the Mooney since the reseal. 

 

The Weep-No-More process is notorious for being bulletproof, and it is probably that more than anything else that has stood the test of time, but I can say that there have been no leaks, seeps, weeps or anything else of any kind coming from my fuel tanks.  So take that for what it is worth.