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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 11:21 
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Joined: 05/11/10
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Location: Indiana
Aircraft: Cessna 185, RV-7
Suffice to say that, as always, things are more complicated than they at first appear. I think it's possible that there's flow through the crossover line or even retrograde flow through the forward fuel lines. Apparently, the fact that fuel is leaving the left tank doesn't mean it's going through the shutoff valve. :ahhh:

Experiments to follow as my education continues. . . .


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 15:05 
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Username Protected wrote:
The CPA has tech note that does a pretty good job explaining this. In short, this is caused by fuel in the crossover vent.

I don’t understand this. The crossover goes between the very highest points in the tanks.


Joe emailed me the paper from CPA. Examination of that and further review of the maintenance manual reveals that the crossover line T's into the forward fuel supply lines from each tank, allowing the tanks to sump into each other in certain conditions, for example, unequal head pressure resulting from unequal venting.

Looking at my vents, the left one measures more or less like it should. The right one was bent WAY inboard, completely blanked by the strut. That's fixed now, but the airplane is otherwise in pieces. I'll have to wait a few days to try it out.

Thanks for indulging me, guys!

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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 15:31 
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Username Protected wrote:
Stuart,

I agree on the quietness of skywagons.org. Its a shame. Patrick

The club site has been dead for years. Everyone is over at the Facebook Skywagon site and/or BCP.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 17:15 
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Had this happen on a 182 with long range tanks recently. The outboard end of the crossover vent line had fallen downward so that it was down in the fuel. The slight (or more) pressure differential between tanks was pushing fuel to the other side until the fuel level dropped enough so that the vent line was above it. But this find was very unusual; I don't suspect this unless the onset of the problem began with some maintenance, especially with integral tanks. Bladders are more suspect because the vent line is just held up by a loop, which holds the crossover vent tubing up at the outboard/forward end, inside the bladder (loop is made out of the same material the bladder is and bonded onto the inner upper surface).

I'll bet you cured 90% of your issue by adjusting the vent behind the strut.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 17:21 
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My C172 would always do the same, until the left tank was just above 1/2, then the right tank would slowly equalize with it. Common Cessna quirk.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 17:59 
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Joined: 08/28/10
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Location: Anchorage, AK (PAMR)
Aircraft: 1966 Bonanza V35-TC
Friend of mine with C185 did a Beech landing near Homer to put out crab pots. One wing lower than the other, fuel started flowing out of the down wing, so he turned the fuel selector to OFF.
Then on take off, he just got into the air when the engine stopped. The fast hands thing wasn't fast enough so he went into the water. Crab pots from the back pinned him against the panel, but his right seat buddy managed to get him free and out.
A barge with a crane happened by, lifted the airplane on board and deposited it on the dock at Homer Spit.
He washed out everything he could with fresh water, squirted LPS wherever he could, and kept flying the airplane. At some later time, with the C185 on floats, he planned to take 2 Labs to a field trial in the lower 48. He landed in Whitehorse, tied up to a dock, and decided to catch a few winks. He laid out a pad and sleeping bag on the dock, then woke up to his dogs barking like crazy. Looking around, he saw the 185 sinking, with the dogs gulping the last bit of air before it went under. He jumped in, opened a door, and let them out.
Months later, after the 185 was resurrected, he asked me to take him to Whitehorse, where he picked up the airplane to fly back to Anchorage.
He later told me that he got into turbulence, and some wet dog food came out of the overhead and down his shirt.
Then he had another sinking in his float spot at Lake Hood. The floats leaked and went under, but this time the bottom was just a few feet under, where the airplane rested until again resurrected.
There are more stories with my now departed friend, including a dead stick dock landing at Whittier with a throttle locked back by lumber in back after hitting turbulence. That was an Interstate.
Aside from all that, he was very much what's called a "good stick".
Moral: You're either lucky or you're not.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 18:50 
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Location: CMB7, Ottawa, Canada
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Stuart,

There is 2 part in your problem.

The first part that you say when the selector is at both and the fuel comes down from one tank more than the other, thats pretty much normal on all these planes. Depending how your vent is setup that might help to even out but you will always see one tank empty faster than the other. I have been chasing that problem for the last 20 years. Its not an issue in the C185 as you have an header tank. So even if one is empty you will not pickup air and the engine will keep going. Like other says if you dont fly with the ball in the center it will empty more on one tank.

The other problem is not normal. If you really think if your tank is set to left that it pulls fuel from the right tank thats an issue and have it looked at. I would suspect the selector as its the only point that will transfer fuel but im not an expert.

From the pilot in AK that sunk his plane because of fuel tranfer moving to the other tank.
Thats why you should always park your plane with the selector either at left or right so fuel does not transfer. We all forget at times and when the tanks are full and you park on an incline, fuel will come out of the vent.

Its a big issue on floats as it could sink the plane if fuel moves all to one side.

Bill, there is no off on the fuel selector on the C185, only a lever on the center console.




Username Protected wrote:
I posted this on the famously quiet Skywagons.org and got nothing. It’s famously quiet, after all. . . .

The airplane in question is a 1981 C185, SN 4181. Here’s the post:

When I set my fuel selector on Both, I always burn more from the left. When I set it to Right, I burn from the right but the left still goes down considerably. Looking through the service manual and talking it over with my mechanic, I’m pretty sure the fuel selector has an internal leak, such that the left tank is never completely shut off. There are no fuel leaks to the outside and nothing leaking into the cabin.

The airplane is having its annual right now. Is this something to fix or something to live with?

Assuming I get it fixed, how hard is it to do in the field with an O ring kit, vs doing an exchange or some such with MacFarlane?

_________________
Former Baron 58 owner.
Pistons engines are for tractors.

Marc Bourdon


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 05 Nov 2018, 19:59 
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Username Protected wrote:
When I set it to Right, I burn from the right but the left still goes down considerably.


This along with the comment you are emptying half a tank before the other comes off the peg are the parts that lead me to believe you're getting some unwanted flow through from the off tank at the fuel selector. I would think it would take an unreasonable amount of pressure through the vents to force that amount of the fuel through the cross over.

Caution: I'm no mechanic just trying to brainstorm for you.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 06 Nov 2018, 13:36 
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Joined: 03/24/08
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Aircraft: Cessna 182M
Username Protected wrote:
The CPA has tech note that does a pretty good job explaining this. In short, this is caused by fuel in the crossover vent.

The crossover vent can convey a serious amount of fuel from side to side. Each little slosh in the tank puts a slug of fuel in that line, to be carried over by any slight pressure differential betweeen the vents. This occurs even if you are only burning fuel from one tank.

You can mess around with the vents and try to make it better, but you'd be my hero if you made it perfect. (By mess around I mean follow the guidance in the MM to adjust them)

If you still feel you have trouble with the valve, be sure to check out McFarlane, they have rebuild kits that might help.


Stuart,

This is the answer. The Cessna vent system may have been designed by a genius but he was having an off day. The cross over vent line can and does carry fuel from left to right and vice versa. I reworked the strut vent to exact compliance with the design specs and reduced the issue in my 182 but it never goes away.

I understood this better last weekend.

I was helping A&P to pull the co-pilot side bladder due to a leak (not fun at all). I did the grunt work including draining the fuel. Plane on ground, level. Drained >42 gallons from the 39 gal tank which was not full to begin with. Finally quit draining, checked other side, was down ~10 gal from start of drain process. Fuel valve was "OFF" at all times - and anyway fuel probably could not flown down from wing to valve and back up 5' to other tank. :) Turned out syphon effect across vent line is real. When I got the tank drained and pulled the vent line it still had fuel in it at the inboard upper vent nipple.

Takeaway is that the vent line clearly can and does transfer fuel, even when plane is level. I "suspect" that it only happens when level in a tank is high enough to cover parts of vent line but not sure.

RAS

PS, to Del's point. The tank I was removing had the vent line end properly held up by attachment in the front, upper, outboard corner of the bladder.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 09 Nov 2018, 09:49 
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Location: Mandan, ND
Aircraft: V35
This does not sound like Stuart's problem, but I have also had this happen when the wings are out of adjustment.

On both, one side would drop faster than other. Ball in center. If you looked out you could see one wing was lower than other. Fly with wings level and ball not in center, would drain evenly on both. Adjusted eccentric on one wing (took a couple flights) and started to drain evenly on both and picked up a knot or two. Flew with wings equal (i.e. One not lower) and ball in center. FWIW.


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 Post subject: Re: Skywagon Fuel Selector Issues
PostPosted: 10 Nov 2018, 11:03 
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Joined: 04/25/14
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Company: wasatch
Aircraft: cessna 180
Stuart, I missed that you were talking about a 185 when I posted my answer on Skywagons.org. The email interface there doesn't always seem to work like the older system. IF you are convinced it is a leak in the selector I would pull it and check for debris that may be keeping one of the sealing balls from closing properly. Everything anyone says about how difficult it is to remove is true. I have had mine out ( a 1953 180) twice and have the scars and enhanced vocabulary to prove it. Once was for a leak around the selector handle shaft, which requires a separate "o" ring, and the second time was for a leak on only one side caused a bit of debris from a piece of interior sealing material from a reconditioned fuel cell.

I have also done 5 fuel bladder replacements, three of which were due to short lived reconditioned bladders. My advice on bladders is only deal with a company run by a Hartwig!

Dick Merrill
Chuckey, TN 04TN


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