Fuel tank vent for C85

[pat williams]

:what is the easiest way to do this mod and do the tanks have to come out. Thanks for the help

[Robert Lees]

Re: Fuel tank vent for C85

Hi Pat,

Which mod is this? I run my C85 using the original wing-top vents for the wing tanks, and the wire gauge for the fuselage tank.

Rob

[flyguy]

Re: Fuel tank vent for C85

On the other hand, mine has venting from the wing tanks through tubing to the center tank which has a sealed cap. I believe the STC I have shows a similar hookup. Mine was not signed off under a STC, but may have been copied in design (a long time ago.) I have a mechanical fuel gauge mounted on the top of the center tank inside the cockpit.

Perhaps the main value of this design is to prevent fuel from venting at the center cap in case of excessive fuel transferred from the wing tanks (?) Never asked, don't know.
DC

[Hank Jarrett]

Re: Fuel tank vent for C85

Unless you leave the valves from the wing tanks to the main open all of the time I doubt your main is really un-vented. If you were running the engine from a sealed tank (which it would be if the transfer valves were closed) the fuel being drained out would create a partial vacuum in the main and the fuel supply would be cut off to the engine. I doubt you leave the transfer valve open all the time which means there is air getting into the main when the engine is running to replace the burned fuel.
I haven't seen your system, but unless there is a second vent line from the main to the top of the wing tank that does not get shut off, you are not safe from overfilling the main in a fuel transfer.
Before I bought my 41 the previous owner was transferring fuel from the wing to the main before the main was half empty (he always assumed the fuel would burn down as the wing transferred fast enough to keep from overfilling). He was WRONG! The fuel came out of the main cap and sprayed in the cockpit through the open window.
Did I mention he had the window open to clear the cigarette smoke? He had just tossed the butt out the window and said he figured the fuel chased the butt down the side of the fuselage. He had been trying to quit for years and couldn't. That was his LAST cigarette!
Hank

If he had been a few seconds slower, it probably STILL would have been his last cigarette.

[flyguy]

Re: Fuel tank vent for C85

As I said, my center tank has VENTING tubing that attaches it to the upper tanks, separate from the fuel lines (which I didn't say). This is also shown on the STC that I purchased (in a panic) before the FAA confirmed that my setup was legal from the 337 originally approved.

The center tank cap is pretty tight but might seep a little if overfilled from the top tanks, but I haven't seen it if it has. Doesn't leak with some pretty goofy negative G maneuvers that I do occasionally.

The VENT tubes are connected to the center tank by a tee on the surface of the tank facing the instrument panel, at the top. The fuel lines come in at the bottom on the same surface (as per usual, I think).
Four lines total.
DC

P.S. Now you have me thinking and I shall have to check the location in the upper tanks of the connections to the lines. This plane had some pretty dumb stuff done to it by the father and son AI's that owned it before me, and I am now wondering if the vent connections on the upper tanks may be located where they are covered with fuel when the tanks are full! It would be typical, Chuckle, and sometimes I do have difficulty getting the tanks to transfer.

Thanks Pat for opening the subject,
Darryl

[Hank Jarrett]

Re: Fuel tank vent for C85

Sounds like I misunderstood your setup and thought the wing to main tank fuel line was used to vent the main. It IS very important that the vent line exit the main at the top (like yours does) and hooks to the wing tank at the top. If the wing tank end of the main vent is submerged, and the main cap isn't tight or there is another "breather" in the main, fuel could transfer through the vent line and overfill the main when the vent is submerged. BAD DAY!!!
A nice trick that helps get the wing tank to drain easier is to fill the wing tank part way FIRST, then open the transfer valve and listen for fuel to start flowing into the main. This "primes" the transfer line so it will start to drain easier. Air in the transfer line can cause the flow to be difficult to start.
Once there is fuel in the transfer line and the valve is OFF you can refuel as normal.
Worked for me!
Hank

By the way, NO ONE smokes near my plane. EVER! My father worked with Gen. Curtis LeMay in the old Strategic Air Command. The stories of him smoking a cigar in a KC-90 were true. He said the tanker WOULDN'T DARE blow up!

[gfortin]

Re: Fuel tank vent for C85

ah yes! Good old Curtis. Remember him well from my USAFE days.