Tom Cook has been ahead of the game since first running an Olympus NL some 7 years ago..........The BVM UAT was originally actually a Jeff Seymour(SWB Turbines) design developed right here in Wisconsin. The semi-permeable sac concept was developed for his UAV projects and was eventually scaled down to the 4 oz size that was compatible with smaller R/C jets using KJ-66 and smaller turbines.

BV has always been conservative in his turbine selections for his birds, and even suggested a P-160 as a suitable motor for the UB....no problem with the UAT....but when guys started going big blocks, especially P-200 and Oly HP in the UB, the standard UAT was incriminated in some fuel starvation flameouts which led to his AD on dual inlets on the center hopper tank.....but there still are tight spots in his recommended setup for the UB.

All goes back to tubing ID as flow is related to the 4th power of the radius, so doubling the radius allows 16X more flow at the same pressure, viscosity, and tubing length.

Tom Cook's unit for big blocks is set up for 3/16"(approximately 4.75mm) ID tubing throughout, in fact he machines a fitting for AMT fuel pumps that converts the input nipple to one that perfectly fits 3/16" Tygon. In addition, he put a perfect shoulder on his nipples so they don't leak without safety wires. I also ran 6mm tubing from my pump output nipple to just before the turbine fuel inlet, saving 4mm tubing for only the last inch, using a Festo reducer.

I did testing on my UB before I lost it to rudder flutter, powered by Oly HPES NL at full throttle and never could demonstrate any bubble in the effluent. Another nice feature of the solid case is that repeated bulging during inflation and collapse during hi-throttle settings on the PE 4 oz UAT Nalgene bottle has led to loosening of the cap and fittings over time and subsequent air leaks......I had started out with a standard UAT with the standard 6mm/4mm tubing setup, but knew that the severe UAT collapse at full throttle, with the sides almost touching was inevitably going to cause problems.......Oli did a nice job describing the results of that collapse....

I do agree it would be nice to have a glass bottle, rather than aluminum, but I have really found that unnecessary in my applications.