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To de-fuel or not to de-fuel that is the question

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To de-fuel or not to de-fuel that is the question

Old 01-08-2007, 01:00 AM
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goodinmw
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Default To de-fuel or not to de-fuel that is the question

Aloha All,
I've always heard, and pretty much always seen modelers defueling their planes after a day of flying. Why?
Obviously if you don't think you will be flying for an extended period of time it's probably a pretty good idea. But if you pretty much know you will be flying the following week (ah paradise) why would it be recommended to de-fuel the plane? I'm speaking primarily of glow fuel, but it would be interesting to hear comments on gas and turbine fuel as well.
It's virtually impossible to get all the fuel out- so there's always some fuel left in the tank. Is the concern that fuel will congeal in the tank and cause blockage?
With the exception of the vent line- the fuel system/tank (at least mine) are as closed as the fuel container the fuel would be pumped back into (also with vent). Jets from what I can tell are totally sealed, in fact I would think a full tank of fuel would be better than an empty one- no air to condense water into the fuel...
Is there a functional reason for this practice- or is it just "good practice". If I recall correctly - full scale light aircraft always keep their tanks full.
Mahalo, Mark

[8D]
Old 01-08-2007, 02:06 AM
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Default RE: To de-fuel or not to de-fuel that is the question

G'day Mark
For a start, full size aircraft don't use glow fuel, ie, methanol, & some sort of lube oil.
I always empty my tanks, then run the motor to get all the fuel out of both the tank & the motor, then when it stops, I try to start it until it won't fire anymore, then use after run oil.
I have seen the aftermath of leaving fuel in a tank, for even a week at a time, the fuel tube is badly effected if left in fuel for a long length of time, as you are suggesting.
And if the tank is not sealed, completely, all the methanol will evaporate away, leaving only oil sludge behind, to block you carby & fuel system.
Old 01-08-2007, 02:36 AM
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HighPlains
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Default RE: To de-fuel or not to de-fuel that is the question

It's good practice to seal the tank when possible after a flying session. I usually try to run the tank out on the last flight, because I don't mine doing dead stick landings. Consider what going into you tank during the flight. Since most fuel tanks are pressurised by the muffler pressure tap, the raw fuel is being contaminated by returned oil and combustion byproducts, one of which is water vapor. So if you pump that mixture back into your main fuel supply, you are slowly degrading the fuel. The only tank that does not do this is the tetra style fuel tank, since the pressure is on the outside of the internal bladder and the fuel remains pure.
Old 01-08-2007, 05:59 AM
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wavy777
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Default RE: To de-fuel or not to de-fuel that is the question

Hi All..

I always empty my fuel tank if the model / tank layout allows...Mainly to allow me to handle the plane back into storage without leaking fuel everywhere. Secondly if the fuel is in the tank for too long it takes on moisture and becomes 'stale'. I no longer run castor (after doing so for 25 years) so leaving fuel in the tank no longer casues gunk.

SO i think the summary must be....if you use castor, empty your tank, if you dont....dont worry about it, but do so if you can easily..

Also running engines dry and adding after run oil is a good idea, but not every week! At the end of a season its a good idea, especially if you run Nitro....

I run 10% Pro-synth fuel..and have done for 3 years, and i have never put after run oil in, just ran the engine dry at the end of each season.....and all of my engines....(mostly OS and ST) are runnning as good as new..and look great inside...

Wavy
Old 01-08-2007, 09:28 AM
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Default RE: To de-fuel or not to de-fuel that is the question

I often leave fuel in the tank. But it's not a good idea. I don't worry about it if the plane is going to be flown again in a day or two, but if it will be more than a week, I'll usually empty it for the reasons stated above.

One reason to always remove the fuel is that if you carry the plane by the tail, the fuel will leak out the vent into the muffler. Then, when you turn the plane upright, the fuel leaks out all over what seems to be the area of the floor that your wife has just cleaned, resulting in yet another week in the doghouse.

Welcome to MY world
Old 01-08-2007, 12:33 PM
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Default RE: To de-fuel or not to de-fuel that is the question

I think the real reason fuel gets "stale" if left in the tank is not the collection of water, but rather the loss of Nitromethane due to evaporation. Since most tanks are not sealed due to the exhaust pressure connection, they are actually vented. This allows nitromethane to evaporate out and escape.

I always pump the fuel out back into my fuel bottle where I can keep it capped.

Brad
Old 01-08-2007, 01:15 PM
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BillS
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Default RE: To de-fuel or not to de-fuel that is the question


ORIGINAL: bkdavy

I think the real reason fuel gets "stale" if left in the tank is not the collection of water, but rather the loss of Nitromethane due to evaporation. Since most tanks are not sealed due to the exhaust pressure connection, they are actually vented. This allows nitromethane to evaporate out and escape.

I always pump the fuel out back into my fuel bottle where I can keep it capped.

Brad
I don’t usually defuel but always connect the carb line to the exhaust line so the tank is sealed.

Bill
Old 01-08-2007, 01:33 PM
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Charlie P.
 
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Default RE: To de-fuel or not to de-fuel that is the question

There used to also be a problem with fuel hoses losing their elasticity and coming off the filler barb or at the klunk. Usually as you pulled up (like on take-off: tres bad). Brass klunks also used to get "gunk" from corrosion fostered by the moisture in the alcohol. Plated ones and stainless don't do it.

Other reasons as above: staleness, moisture absorption, spillage risk.
Old 01-08-2007, 01:35 PM
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Default RE: To de-fuel or not to de-fuel that is the question

What I do:
Empty the tank as much as I can, then start the engine (which runs a few seconds). Finally, I apply after run oil... With this procedure I'm sure that engine never has problems for the next week.
Bye!
Old 01-08-2007, 08:33 PM
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a65l
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Default RE: To de-fuel or not to de-fuel that is the question

I've bought enough used planes to become convinced that fuel left in the tank or engine is a very bad idea.

Andy
Old 01-09-2007, 08:29 PM
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propbuster
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Default RE: To de-fuel or not to de-fuel that is the question

We always top off the fuel tanks on full size light planes after flying to reduce the amount of air in the tank, which of course conatins water vapor, and with changes in temperature will condense into droplets hence contaminating the fuel. This happens all the time even with the tanks topped off as practically possible, so in your prefight routine, we have a drain on the bottom of each tank as well as in the engine compartment to remove the water that has accumulated on the bottom.
Old 01-09-2007, 09:31 PM
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Default RE: To de-fuel or not to de-fuel that is the question

G'day Mate,
If the water didn't mix with glow fuel, & we could just drain it away, that would be fine, but it does, & the glow fuel degrades silicone tubing, so I always defuel, at the end of the day, & run my motor out of fuel, & add afterrun oil.
But you are welcome to do whatever you want with your planes.
Old 01-09-2007, 11:07 PM
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goodinmw
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Default RE: To de-fuel or not to de-fuel that is the question

[8D] Mahalo All, (Thanks)
Having just returned to the hobby after 20 years it's amazing what technology has done- and these forums provide such a useful, efficient and timely mechanism for distribution of information and experience it's great. Thanks for all your support and feedback. I think for the tanks I can't easily empty I'll fill the tank and cap the vent line which should minimize the air to fuel ratio, at least less than what would be in say a half filled gallon container of fuel. I'll watch close and let you know if I run into any problems. I run OS engines and have never had problems.
Mahalo again, Mark [8D]
Old 01-10-2007, 07:19 AM
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blikseme300
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Default RE: To de-fuel or not to de-fuel that is the question


ORIGINAL: bkdavy

I think the real reason fuel gets "stale" if left in the tank is not the collection of water, but rather the loss of Nitromethane due to evaporation. Since most tanks are not sealed due to the exhaust pressure connection, they are actually vented. This allows nitromethane to evaporate out and escape.

I always pump the fuel out back into my fuel bottle where I can keep it capped.

Brad
It is not so much that the fuel gets stale. If you are living in an area that has very high humidity then the methanol will absorb water. We see this quite often here in deep south Texas. Not only fuel left in the plane, but the fuel jug itself.

Contrary to popular belief, methanol in the engine causes corrosion, not the nitro. For those who don't believe this, do a simple test. Take 2 plastic containers, half fill each with methanol in one & nitro in the other. Place a piece of steel in each. Leave for 24 hours. Observe after this period. Even when running FAI fuel you will get corrosion. (FAI fuel has NO nitro.)

Yes, half burnt fuel does accelerate corrosion inside engines, but is not the main culprit, methanol is. Run your engines dry.

Safe Flying!
Old 01-10-2007, 07:48 AM
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Default RE: To de-fuel or not to de-fuel that is the question

Methanol is hydroscopic (it absorbs water)!

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