Offloading fuel

[wpilot673]

So you’re planning a flight for the next morning  and realize that you have too much weight.  For whatever reason you can’t take out baggage or passengers. You must offload some fuel.  ( yes, you will still have plenty of reserve in this hypothetical situation )  Have you done this and what’s been your experience ? 5 gallon jugs ? Siphon hose ? Ground strap ? 

[N6758N]

Go flying!

[wpilot673]

Other then go flying.  Lol

[201er]

2 minutes ago, wpilot673 said:

Other then go flying.  Lol

I second go flying. And I have hundred gallon tanks! Basically I try to plan heavy loaded flights well in advance so that the flying I do leading up to it has the fuel where I want it. I just don't do pop-up heavy flights unless it happens to be low already. Which leads to my other point is keep the fuel low and fuel before flights if you expect unexpected heavy loaded flights.

[jaylw314]

Unloading fuel would be less of a problem since you can put any fuel canister on the ground to ground it. 

Putting the fuel back might be more of an issue.  Is there a risk of static discharge when you pour fuel from a portable tank directly into the wing tank from above?  Or are you supposed to leave it on the ground and use a hand pump?

[neilpilot]

5 hours ago, jaylw314 said:

Unloading fuel would be less of a problem since you can put any fuel canister on the ground to ground it. 

Putting the fuel back might be more of an issue.  Is there a risk of static discharge when you pour fuel from a portable tank directly into the wing tank from above?  Or are you supposed to leave it on the ground and use a hand pump?

Please don't confuse a container on the "ground" with it being electrically grounded. The way to avoid a static discharge is not to "ground" the container, but to electrically "bond" it to the wing.  Also remember that many gas containers are plastic, and will not conduct.  So try to avoid free-falling liquid, and if possible inset the transfer tube subsurface or just above the containers liquid surface.

[Yetti]

Concrete makes for a really poor grounding media

[jaylw314]

2 hours ago, Yetti said:

Concrete makes for a really poor grounding media

Yes it is poor, but if you have 1000x the contact area compared to a wire, it's pretty good. 

 

14 hours ago, neilpilot said:

Please don't confuse a container on the "ground" with it being electrically grounded. The way to avoid a static discharge is not to "ground" the container, but to electrically "bond" it to the wing.  Also remember that many gas containers are plastic, and will not conduct.  So try to avoid free-falling liquid, and if possible inset the transfer tube subsurface or just above the containers liquid surface.

Yes, I was specifically thinking of plastic containers.  Ideally, a metal container should be grounded to the airframe.  Since you can't do that for plastic, the only thing would be to place it on the ground, since the airframe and ground voltages equalize over time if the plane is standing still.  At least draining fuel should not build up a static charge on the airframe.

I get that fuel builds static charge falling through air, but does it also build a static charge flowing through an insulated tube?  That would also seem likely, but I don't know how significant that effect might be?

[bonal]

9 minutes ago, jaylw314 said:

Yes it is poor, but if you have 1000x the contact area compared to a wire, it's pretty good. 

 

Yes, I was specifically thinking of plastic containers.  Ideally, a metal container should be grounded to the airframe.  Since you can't do that for plastic, the only thing would be to place it on the ground, since the airframe and ground voltages equalize over time if the plane is standing still.  At least draining fuel should not build up a static charge on the airframe.

I get that fuel builds static charge falling through air, but does it also build a static charge flowing through an insulated tube?  That would also seem likely, but I don't know how significant that effect might be?

The ground wires should be connected to a proper copper ground rod driven into earth. Plastic is very good material for generating a static charge. A metal can on concrete is a VERY poor ground.

[RLCarter]

Plastic containers are more likely to have a static charge than a metal container. I've drained several planes into plastic containers, use a little common sense and there isn't an issue, if your worried touch the aircraft somewhere on a non painted surface and the container to be used at the same time

[EricJ]

What you really want is that the airplane and the fuel container are at the same potential.   If the airplane isn't electrically grounded to earth, then it may be at a different potential than the local earth reference (e.g., a rod or pipe stuck in the ground), so grounding the container to earth reference may not be productive, either.    When the fuel truck comes he doesn't care whether the fuel truck or the airplane are at earth ground, just that they're the same, so running the clip between the truck and the airplane accomplishes that.   Since they're both on tires that insulate from the ground reasonably well they still may not be at earth reference, but if they're at the same potential as each other there won't be a static discharge spark when any pieces of them  touch.

How to do that with a plastic container?   I don't have any good ideas, since plastic isn't very conductive.

[ShuRugal]

Doing a bit of research on this subject, it appears that there are fuel jug plastics which have carbon added to them to prevent buildup of static charges.  I came across the following advice to find out of the fuel jug you are using is in danger of carrying a static charge:

 

Quote

One thing you might want to try with your HDPE tank is to rub the surface with silk or maybe polyester cloth. Then turn the back of your hand/forearm to the area where you rubbed it. If it's building static, then it will pull up on the hairs. If it has some sort of static inhibitor (like carbon), then it will dissipate the static very quickly, or possibly not build the static in the first place.

 

If your jug passes this test, then it will be sufficiently conductive that you should be able to affix a copper grounding braid to the handle and clip it to the plane to equalize any charge.  You could additionally verify this by measuring resistance between the plastic can and the end of the grounding braid.  If the resistance is under 1 MΩ, then it should equalize to your plane fairly quickly.

[jaylw314]

 

2 hours ago, ShuRugal said:

Doing a bit of research on this subject, it appears that there are fuel jug plastics which have carbon added to them to prevent buildup of static charges. 

I guess the question is how high the risk is with normal plastic jugs.  If the risk is almost zero, as I suspect, conductive jugs would probably not be worth the cost.

Most of the Darwin awards you hear about are people filling jugs in the back of their pickup truck.  Then it wouldn't matter at all if the jug was conductive or not...

[xcrmckenna]

I have unloaded fuel a few times already to give me a little fudge factor. I like flying with 40 gallons. Still gives me plenty of distance. I have four of these that I’ve used from my dirt bike days. The wide opening makes it easy to siphon fuel out of the plane and the long hose makes it really easy to put the fuel back in.




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[carusoam]

Nice old jugs...

Can you put it under the fuel strainer drain?

Have somebody Pull the ring in the cockpit while you watch the level in the jug.

Emptying the tank this way doesn't require a siphon, or pulling a drain plug or any tools....

Holding the ring up can be done gently with a 'pry' tool.

these are untested ideas of a PP, not a mechanic with good ideas...

+1 on grounding wire between plane and jug. Especially in the dry air of winter... even an imperfect copper wire solution is better than skipping this step..

Best regards,

-a-

[kortopates]

The risk isn't limited to defueling/refueling the plane. You also have the storage issue to consider next. Fire ordinances and the like typically prohibit storing fuel in the hangar that is not in the plane.

 

 

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Edited December 22, 2017 by kortopates

[Raptor05121]

I used this to pull the last few gallons out of my wing for weighing it:

[M016576]

28 minutes ago, Raptor05121 said:

I used this to pull the last few gallons out of my wing for weighing it:

The drain plugs are only torqued into the wing at 15 Inch-lbs.  very easy to back out and let the wing completely drain.  

Back out the drain until the tension breaks, then just hand screw the rest.  Fuel doesn’t start leaking until it’s about 3/4 of a twist off the torque- so by that time you’re not using a tool, just your hand.  I keep a box of latex work gloves in my toolkit for working with oil, avgas and TKS.

the grounding piece has been beat to death above- but a stray spark could really ruin your day... 

once you’re happy with however much fuel you’ve drained, hand screw the drain back in (it will stop leaking just with hand tightening, and tighten to 12-15 inch-lbs of torque.  Any more and you’ll shear the head off the drain.

this method has the benefit of draining out any sediment that may have accumulated in the wing, too.

[Sean S]

Disconnect the fuel line at the firewall, attach a line to the fitting, put the other end in a container and turn on the boost pump. You can select which tank to drain using the fuel selector.

[jetdriven]

There

58 minutes ago, Bayern Speed said:

Disconnect the fuel line at the firewall, attach a line to the fitting, put the other end in a container and turn on the boost pump. You can select which tank to drain using the fuel selector.

There are several instances of people burning out their electric fuel pumps doing that. Overhaul of those is over 1000$ now too.  The Dukes pump is not rated for continuous duty. The Weldon is.

[Sean S]

There
There are several instances of people burning out their electric fuel pumps doing that. Overhaul of those is over 1000$ now too.  The Dukes pump is not rated for continuous duty. The Weldon is.

Draining 10 gallons of fuel is not continuous duty. Plus, with the line disconnected it is a low load on the pump.


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[jetdriven]

I know that, but Ive read at least three different occurrences of pilots draining the fuel from their plane with the Dukes fuel pump and it ruined it. None of them said it was a full airplane, but still, its a 1200$ repair and is not any easier than unscrewing the wing drain port and draining into a grounded can.

[kortopates]

24 minutes ago, Bayern Speed said:

Draining 10 gallons of fuel is not continuous duty. Plus, with the line disconnected it is a low load on the pump.


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I know someone personally that lost their electric boost pump trying to drain a mere 12 gals! Maybe it was on its last legs anyway but @jetdriven Byron's caution is very valid.

[xcrmckenna]

With a 1/2 clear hose I can siphon 10 gallons out of a tank before someone can take their cowling off, disconnect a fuel line, hook a hose up, turn on the master, and fuel pump.


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[whiskytango]

16 hours ago, kortopates said:

The risk isn't limited to defueling/refueling the plane. You also have the storage issue to consider next. Fire ordinances and the like typically prohibit storing fuel in the hangar that is not in the plane.

 

 

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You should also check your hangar lease and liability insurance to see if there are any prohibitions against storing fuel in containers.  In the unlikely event that something bad happens you don't want your insurance coverage declined.