My next question is about the Siphoning phenomena. Ive read filing the vents help prevent this, But since the tank sits enclosed in the fuse, can he attach a vent on the inboard side of the fuse pointed into the airstream or does he just run both top and bottom vents straight out of the top and bottom of the fuse like you have stated? My goal is to minimize any fuel blowing out of the tank vents on to the finish. Sorry if it sounds like I'm being Difficult. I guess what I'm trying to get at is whether he should or should not use the 'L' shaped vent on the inboard side of the fuse.
Kevin
Unfortunately none of the above solutions work all the time. While it kinds of makes sense to try to put positive pressure on each vent (by angling the ends or aiming them forward), what frequently happens is that air will come in one vent and fuel will be forced out the other vent by the pressure. The fact that the engine happens to also be sucking fuel out is almost irrelevant because the fuel flow rate is negligible. The fuel blowing problem will keep happening until both vents are in the ullage. It doesn't happen every time, but is common enough that if you are worried about raw fuel you don't want to use it as supplied
The more reliable solution is to make sure that at least one vent goes all the way to the top inboard edge of the tank, and the other can be anywhere, because all you are going to use the second tube for is fill the tank, and then plug it after it you fill. This is exactly like a uniflow tank, just with the uniflow vent on the inboard side instead of somewhere toward the edge, so you get a falling fuel pressure the entire flight. This is much less prone to the "unwetted tube" leakage because, more or less, there is no fuel at the vent after you have run 30-45 seconds, even inverted under maneuvering.
It is less clear that this will work well with the typical Bi-Slob flight, where the fuel would be expected to be all over the place during the crazy gyrations. My best guess is that in addition to the very top and inboard corner, you also want to put the vent tube as far forward as possible, so it stays uncovered when in hover or other post-stall flight.
But I am curious - the ARF BiSlob is monokoted even on the fuse, so, aside from the mess and loss of capacity, it should be pretty immune to raw fuel. Many a very nice Nobler, built straight off the Green Box plans including the tank and finished with dope, have been messed up by raw fuel from the standard tank blowing out in a stream for the first part of the flight. The mess is assumed - with typically no muffler and Fox Superfuel, all that oil goes everywhere anyway, and the raw fuel is a minor consideration.
Brett
Topic: Standard tank in a full Fuse (Read 801 times)