Re: Q200 fuel vent


French <LJFrench@...>
 

Earnest,
I have been an advocate of a good sound design for the vent system on our Q's that would be foolproof enough to avoid the need for the complexity of a boost pump. I am at the point where I have the option of designing the header tank for my Q'Vair and you bring up a good point that I have been pondering - install the secondary vent at the front of the header tank and the main vent per plans.Right now I'm thinking about an integral overflow system that would also span from the front of the header to the back of the header where it would Tee together down the common 5/8" tube to the main tank. Both the main and secondary vents would be incorporated into these overflow channels. No matter what the flight attitude, one end of the header would be always be vented. Also was thinking about making the secondary vent orifice small compared to the tube that it attaches to. Thought being that not enough fuel could bleed through the orifice so as to completely fill the tube which then creates the blockage issue. I don't know, still work in progress on some of these ideas.
The vent out the top of the fuselage is probably the best of all options for venting, it's just that it has some of the other negatives that could maybe be engineered out. Also has the risk that if the aircraft ever inverted for whatever reason, the header eventually completly empties out onto the ground and hopefully there is not any other ignition sources around. Maybe designing some baffling inside the tank might reduce the chance for fuel to splash out. Also, if it could be hidden and channeled or routed somewhere else to get the ram affect would also help.
Jim would have to speak for his type system, but it seems that the overflow tube/vent tube system still exists which part of what we are trying to keep from getting flooded under certain conditions.

Still looking for the perfect "feel good" system.

Lynn

Ron,
I have a completely stock system. When the main and header are full and
you accelerate or rotate, fuel in the header moves to the rear of the tank,
fills the down pipe which in turn fills the vent. I have seen this many times
on the ground when I press down on the tail to move the plane around on the
ramp immediately after fueling. Fuel pours out the vent.
I am beginning to wonder if this is not a bigger problem in Tri gears
since tail draggers are already in a climb angle when sitting on the ground. I
think, but have not tested, the theory that a drain pipe and vent in the
front of the tank would be less susceptible to this problem.

Earnest






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