GBR Jet pleated paper clunks... great product!

[Kiba]

After having a couple of fuel system issues that resulted in a flameout I decided to change all the fuel tubing on the heli and the membrane sock in the BVM UAT.

While buying fresh fuel line and the UAT membrane sock I came across these pleated paper clunks from GBR-Jet.

http://www.gbr-jet.com/catalog/produ...ei5b6troem1hd3

I decided to pick up a set of the 6mm clunks and give them a try. First impressions are they are very nicely made. There are no sharp burrs and all the edges are rounded and smooth to help minimize wear of the fuel tank (my previous brass clunks had a fairly pointy end and actually left a wear ring in the aluminum fuel tanks.) The pleated paper portion provides a lot of surface area for fuel pickup in addition to filtering fuel headed to the fuel pump and turbine. At 28g they are decently heavy so they should still move around adequately even with slightly older or less flexible fuel tubing.

Flight results... in a word, fantastic. For the first few flights of smooth 3D the UAT was totally full when the heli landed. By "totally full" I don't mean there was 1/2" of air at the top of the UAT after landing; rather it looked like I had just fueled the heli and there was only a tiny bubble of air at the very top of the cap of the UAT. A few more flights, each one more aggressive, showed the same behavior-- nearly no air in the UAT after landing. After some more testing and going progressively longer on flight times it was evident the GBR clunks were capable of pulling the main tanks nearly completely dry before they would start sucking air even when subjecting the heli to aerobatics.

While these clunks are a little on the expensive side the quality of construction and more importantly their performance is completely worth the expense in my opinion.

The next product I'm interested in from GBR is their air trap...

http://www.gbr-jet.com/catalog/produ...products_id=65

It looks like it will fit on my heli in the same spot as the BVM UAT. Unlike the membrane sock of the BVM UAT the GBR Jet piece uses a large centrally located pleated paper element for fuel pickup. I also like their sealed design that eliminates the possibility of drawing air into the system from a loose cap or poor teflon tape on the cap of the BVM UAT design.

[cbdane]

They look great! I have two but unfortunately, they didn't fit through the necks of the Kevlar fuel tanks on my jet. I had already back-flushed them as recommended as was in the midst of installing them when I discovered it. Check this out in advance!

[Kiba]

Good point Brent, the GBR clunks are a little large in diameter. Not a problem fitting through the openings of the SIGG bottles on my heli but I can see it being a problem with some Kevlar tanks in airplanes.

While my rebuilt BVM UAT is working great I may swap it for a 130ml GBR air trap once Dreamworks gets them back in stock. Either that or I'll run the freshly rebuilt BVM UAT for another year or so and swap it out for the GBR air trap at the same time I do my yearly fuel line replacement.

[SimT]

Thanks for pointing these out.
I am just about to sort out my fueling and was thinking of turning up some heavy brass clunks to go into the Sigg bottles so these will do the job.

I have not got an air trap yet so also interested in that. Could I use that air trap vertically as well as horizontally?

[Mercuriell]

Those airtraps do look nice, they say any orientation and also mention an internal pleated filter so wonder if thats similar to clunk filter ..

I also like the look of these, easy to see whats going on inside !

http://www.intairco.net/categories.p...er-Flow-Series

[SimT]

They may say any orientation any way but text is a bit small for my eyes.

[Kiba]

Originally Posted by SimT

Thanks for pointing these out.
I am just about to sort out my fueling and was thinking of turning up some heavy brass clunks to go into the Sigg bottles so these will do the job.

I have not got an air trap yet so also interested in that. Could I use that air trap vertically as well as horizontally?

You can mount the GBR air trap horizontally so long as it is rotated to place the fitting that connects to the main tanks at the highest point so air is forced out during fueling.

[cbdane]

Keep in mind, though, that a disadvantage of these types of UAT is that they won't tolerate air levels below ~0.5 (pleated internal filter on a stiff stalk) while the BVM style has the ability to almost empty the UAT in case that's required. Sounds like the GBR clunk helps address this issue but without this type of clunk, I'm going to stick to the big sock.

[Kiba]

Good point Brent, with the BVM style the sock occupies a large portion of the volume of the entire bottle and as long as the sock is partially submerged in fuel it will continue to draw fuel. With the sock occupying a large portion of the bottle in a Hansen or BVM UAT even at very low fuel levels there's a very strong chance at least part of the sock will remain in contact with the fuel. With the GBR UAT the pleated paper element is centrally located and mounted on a rigid brass tube so more fuel must remain in the GBR trap such that the paper element stays in contact with the fuel.

One test I've found on the internet shows the GBR will start allowing a bit of air into the system once it gets down to about 1/4 fuel remaining-- certainly not quite as good as a BVM or Hansen UAT that uses the sock and can pull down to nearly no fuel remaining. That same test also shows the GBR is one of the best out there when it comes to cavitation performance and while that may be a valid concern for larger turbines with higher fuel flow rates it's not too much of a concern for the relatively low thrust / low fuel flow Wren 44.

Chances are I'll stick with the GBR clunks and the BVM UAT since that setup works perfectly. It's possible to squeak out another 45-60 seconds of flight time with the GBR clunks compared to regular clunks on my heli before any air starts being pulled into the UAT.