With my heli's, I fly with a weighted klunk and a thin walled tube to allow the klunk to follow the fuel around the header tank. Getting into jets now I see a lot of people use juat a straight peice of brass tube with a stone or felt as the klunk, but it does not follow the fuel around the UAT. i think the theory is the placemnent of the pick up point of the klunk should always remain in fuel.
Interesting theory and from most accounts it works but I am interested in some more opinions.....
Can anyone champion the virtues of one over the other?

Max,
A UAT, as designed by Jeff Seymore and marketed by BVM does not contain a "Clunk weight" of any kind.
Instead, it contains a filter "sock" membrane, as found on the inlet of submerged automobile fuel pumps, with a waffle type plastic separator to keep the sides of the sock apart. The fuel saturated sock supplies the engine with the fuel, both acting as a filter, and an air separator. A large enough bubble will shut a turbine down immediatly.l

An "Air Trap", as is used on ducted fan applications, is a small tank with the pickup tube located in the geographic center of the tank. No clunk weight either. It is supposed to remain submerged in fuel to eliminate the possibility of sucking air.

If the jets you are looking at do not contain the BVM type UAT, (and there are several manufacturers selling very similar items) they are using what I would call a a "Header tank". That's what you are using in your heli's.

No matter how you do it, or what you call it, the pickup must remain submerged in the fuel, or you will suck up air. That will make the engine very quiet all of a sudden.

See [link=http://www.bvmjets.com]BVM Jets[/link] for more information on the UAT.

Cheers,

Harley Condra
BVM REP
JetCat REP

I see, I like the looks of the the BVM one but it seems quite small, is it suitable for larger >30Lb turbines?

Yes, it works fine with the large thrust turbines. I've been running one without problems in an AMT Olympus (45lbs) for several years. Bear in mind that the function of a UAT is not as a fuel supply but a mechanism to supply a constant flow of bubble free fuel to the turbine in all flight attitudes. Fuel in the UAT should be considered "unusable" and you should look elsewhere if more is needed (i.e. larger main tank, aux tank or header tank).

Craig

Quite adequate. The BVM 4 oz UAT is the de-facto standard. (In fact even the term UAT is a BVM term, sort of like pointing to a box of Puffs and saying "pass me the kleenex). Someone, don't remember who, sells an 8 oz. That is , I think, just to put more fuel on board and not because the 4oz wont do the job.

Think of it as an air trap, not as a header tank.... there are a few different designs, and they are meant to remain full of fuel throughout the flight....