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Heated fuel vent?

REPLY

My point is, that small surface areas pick up the ice first, not the blunt projections. With the check valve at the top of the vent loop it is above the level of the tank, so no fuel would exit, should it fail. I simply like to have a backup means to vent a tank, other then two externally exposed screened probes.

You made a good point regarding the amount of air at the wing root. But with it sealed and using thick plumbers pipe insulation should help.

Once again thank you so very much for your replies to this inquiry.
 
Some times it hard to type what I am thinking

Kahuna said:
Kent this is an interesting idea. Lets talk this through. Can you elaborate on the issue your trying to solve with this? Im not following.

One senerio. Im picturing this little ball of water striking my above freezing outside vent tube (warmed by the cowl air mostly) traveling along the vent system with outside pressure pushing and my fuel tank pulling, through my warm toasty cabin, into the wingroot where is cools some, and along the inside of the cold tank where it freezes before exiting into the fuel area. This is my best guess of what happened to me. Whats the check valve going to do? Or are you after a different set of crcumstances?
Click to expand...



If where I have glued the wire I had made a low spot, say bend down a loop of a couple of inches (or may be do a full loop) and on the tank side place a check valve. Any water in the tank side of the line should flow to the fuse and collect in the low spot. If it freezes the vacuum that develops in the tank would open the check valve and bring air from the root.
Any blockage latter in the system would also cause the check valve to open.

Kent
 
Heated Fuel Vent

I think it would be instructive to discuss how high performance aircraft, especially those certified for known ice, do their fuel vents to see if any ideas are applicable to our aircraft.

The Piper Seneca has the fuel vents in a removable access panel in the lower wing skins at about 50% chord. The panel has about a 4" x 4" pyramidal shape inset about 1" into the wing. The fuel vent is located on the aft face of the pyramid facing into the direction of flight. So nothing protrudes into the airflow for ice to form, yet the fuel vent seems to be located in a region of positive pressure.

An earlier post mentioned Aero Commander fuel vents mounted to the engine baffles. I would still like to see a schematic of this system.

Does anybody know how Mooney, Beech Bonanza, Cessna 350/400 Corvallis, or Piper Malibu do their fuel vents?
 
Heated Fuel Vent

Although I realize FARs only apply to certificated aircraft, they may be useful for guidance for our experimental aircraft. I found the following in FAR Part 23 regarding fuel tank vents. Note especially (1), (5), and (6). Not sure if my recommendation of adding a check valve as a backup suction vent to the standard under fuselage vent violates (6) or not. I believe the check valve prevents fuel or fuel vapour from entering the personnel compartment in any configuration. Opinions?

Sec. 23.975

Fuel tank vents and carburetor vapor vents.

(a) Each fuel tank must be vented from the top part of the expansion space. In addition--
(1) Each vent outlet must be located and constructed in a manner that minimizes the possibility of its being obstructed by ice or other foreign matter;
(2) Each vent must be constructed to prevent siphoning of fuel during normal operation;
(3) The venting capacity must allow the rapid relief of excessive differences of pressure between the interior and exterior of the tank;
(4) Airspaces of tanks with interconnected outlets must be interconnected;
(5) There may be no point in any vent line where moisture can accumulate with the airplane in either the ground or level flight attitudes, unless drainage is provided. Any drain valve installed must be accessible for drainage;
(6) No vent may terminate at a point where the discharge of fuel from the vent outlet will constitute a fire hazard or from which fumes may enter personnel compartments; and
(7) Vents must be arranged to prevent the loss of fuel, except fuel discharged because of thermal expansion, when the airplane is parked in any direction on a ramp having a one-percent slope.
(b) Each carburetor with vapor elimination connections and each fuel injection engine employing vapor return provisions must have a separate vent line to lead vapors back to the top of one of the fuel tanks. If there is more than one tank and it is necessary to use these tanks in a definite sequence for any reason, the vapor vent line must lead back to the fuel tank to be used first, unless the relative capacities of the tanks are such that return to another tank is preferable.
(c) For acrobatic category airplanes, excessive loss of fuel during acrobatic maneuvers, including short periods of inverted flight, must be prevented. It must be impossible for fuel to siphon from the vent when normal flight has been resumed after any acrobatic maneuver for which certification is requested.
 
YES! it is definetly possible

i read an article the other day on VAF that discussed this very issue. he was ferrying his rv to Europe and had 2 tip tanks, mains and a custom tank on his passenger seat. luckily he had the ferry tank and tip tanks cause the vents froze up on him over the ocean. check out the story,,
http://www.vansairforce.net/rv_travel/FlighttoFrance1.pdf
 
Heated Fuel Vent

Thanks for the NACA references. Further to my post of Feb 18 here are a couple of views of a Piper Seneca fuel vent that I made (didn't have a camera with me at the time so I made a CAD model). These are not too different from the NACA recommendation

This is a section of the fuel vent that is mounted about half chord on the underside of the wing. Direction of travel is from right to left.
http://tinypic.com/r/qyzc0i/5
This is an isometric view. Tank vent is the hole on the aft face of the pyramid. Should be in an area of positive air pressure but since it is inset into the skin of the wing precipitation has nothing to form against.
http://tinypic.com/r/2ewioty/5
 
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