I have seen many posts here stating the use of large header tanks, 38 oz for instance.
It's been my experience a header tank s/b small, so as not to pick up air.
I have a 2 litre pop bottle tank in my Roo, and it would flame out at half tank or so.
I installed a two oz header tank and no more flame outs.
Seems to me the large tanks allow sloshing of the fuel when it gets partially empty and the clunk is exposed to air.
Probably why some tanks use baffles inside.

Any thoughts on this?

Just use your fuselage as a header tank. There is enuff fuel sloshing around in it already

Go here: http://www.jetpilots.org/how_to_buil..._pleated_p.htm

I use one of these home made clunks and a Dubro 20 oz or 24 oz header with BVM aluminum caps and have never had an issue. I use a main tank with a regular jumbo weighted clunk (no pleated paper) and I typically have just a tiny bit of air in the tank on landing. If I fly a very long flight and I think that I may be eating into the header, I just keep it calm and use the header fuel to get me through the pattern for a landing. But with even a half empty header and the fact that the clunk can be 95% exposed to air and STILL draw fuel only, I am confident I could do some violent manueavers (but I don't). Since I've been using these, I have never had an unexplained fuel system flame out.

I did build one of those filter clunks, but I got the bright idea of putting in my 5 gal fuel tank. The high volume pump I used sucked the thing shut and the paper kind of mashed all together and wouldn't pass fuel after that. Never got around to making another one.
My little header tank with a clunk works good. I do cuban 8's, loops, rolls etc and it runs fine.
Have landed and taxied back with just vapors in the header tank and it's still running. Amazing!

I think that paper filter clunk is a good idea, those paper filters filter to about 10 micron's I believe.
I have a large paper one in the line from my 5 gal tank I use to fuel my plane.
Haven't had to clean a filter since I put it in.
I check them and they're always clean.

Wow. You don't need to worry about it collapsing in your plane though, not enough flow rate.

You must have read my post, but not well enough because you might have noticed that I decided not to use that 38oz header tank. I built the tanks to fit inside the available space in the fuse, and they wound up being way too big. The tank that was going to be my header tank was intended to be about 16 ounces, but I misjudged just a little because it came out at 38ounces. That is way too big for a header tank!
The main tanks came out bigger than I thought too, so I don't need the extra fuel anyway. I will probably use a 6 or 8 ounce sullivan tank for my header.
The 38 ounce tank that I made will not go to waste though, it will still fit in there and can be used later as a smoke tank.

Kevin Whitlow
Jetcat rep.

Pete,

You said you have never had a "unexplained fuel system flame out"...What would you consider the explainable ones?

I read your post and that seems like un-wise fuel management on your part to fly untill your tank is empty. You could get away with that on a Sig Kadet, but a turbine airplane requires more responsibility..

Just my thoughts,

Burt

Explainable flame outs: I had one flame out, years ago, just after starting to use the pleated paper clunks when I had too severe a bend on the suction side of the pump at the Festo check valve that started to let a bubble stream in. My fault, in no way the fault of the clunk system. I had another when I forgot to replace the plug in my fill line and took to the friendly skies. I had a very old original 750 pump go belly up. I had lots of bearing failures with the old engines I used to fly (but those were not fuel system related).

Come on Burt, read what I wrote. I have only flown till empty once and that was in the original Isobar just to see how well I could scavenge the fuel. I flew a normal long flight then went upo high and, of course, it seemed to take forever to drain the last drops. Finally she quit and I landed uneventfully on a 400 foot grass strip (no big deal with a well designed plane like a Bar). I was EXTREMELY impressed with what I saw in the tanks. Bothe the main tank and the header were basically dry, just residue on the bottom. If you tilted the plane over to one side, you could get a few drops in the corner, but that was it. So you see, after that test I have confidence in this system and it has yet to let me down (wish I could say that about all of the other components!). But I never really push it. Its just that if I am at a big jet rally and have flown a long flight and need to land and Terry Nitsch needs to land a gazillion dollar jet right now, I know I can go cruise around at ¼ throttle for some time and be fine.

Just my reply!

Burt,
I never mentioned unexplainable flame outs.
The times I landed on vapors was unintentional.
I had to make an extra go around after my beeper went off, and I had apparently been using full throttle a bit too much.
Nice to know I can do it though.

Landing on vapors, and without fuel happens it does not mean the pilot is irresponsible. I was flying a Bobcat that we had determined a flight time with based on flying it off pavement. I flew it from grass for the first time and used the same timer settings. I was very confident in my abilites (and the airplanes) to be able to land without having to do a go around, its a good thing, because I forgot to take into account the fact that it uses a bunch of extra fuel up to taxi on the grass. I had a BVM UAT in the plane and it functioned very well, after the first flight when I did get back and shut the engine down there was about an ounce left in the UAT. Needless to say I was impressed, (not smart enough to adjust the timer though) the second landing was dead stick, and for some reason the engine just would not run without fuel......go figure.


David Reid