Bladder tubing is available from Phil at the Core House . The regulators are a left over from the Fox era of combat . They work but can be a PIA to maintain. Procurement might be an issue .

Howard Rush employed the dark arts of west coast combat tech as Mr. Walkers mechanic. I was fortunate enough to watch the B-17 fly . Still marvel at the starting routine and pit discipline . NASCAR would be proud .

Brad   

The first pressure/regulator system I saw was the Jim Walker system in old Air Trails mags around 1950. This system used a rubber rectangular shaped bladder that was sandwiched between two smooth plywood pieces with rubber bands wrapped around them. The bladder was connected to the pressure regulator (which was a small 3/4" diameter by maybe 3/16" thick), that was mounted near the venturi of the engine. The issue with this system was it was very touchy to dirt (as are most regulators). Today we have fairly easy ways of filtering our fuel as it comes out of the can and before it goes into the tank. Who made the regulators and are they available?

Best,   DennisT

Tony Huber made the regulators.  Bladders in general are not good stunt tanks because they aren’t stable when the engine is running on the rich side of peak RPM.  The richer it gets, the richer it gets.

From what Howard said the problem is they don't work well with normal stunt engines running slightly rich. This seems similar to the problem of running some engines (for me it was the Fox 35) on uniflow muffler pressure. Seems with a normal stunt venturi you get the two systems fighting each other pushing/pulling and the run goes all over the place. This seemed to be the same problem with base pressure if you had a suction venturi.

What about opening up the venturi to reduce the normal suction and let the fuel system deliver the fuel, the regulator keeping the fuel pressure constant and the venturi deliver the air ?

Seems that the pressure system would give a couple advantages: neutral CG as fuel burns off if the tank is located at the CG - giving positive weight loss change; or would allow trimming of the CG shift by allowing the tank to be located either forward of the CG or aft of the CG to have the ship go have a slightly nose or tail shift in CG as fuel burns off.

Might need to mess with prop loading to get vertical pulling with the engine at more of a constant rpm, but that is a separate issue once we get the engine working smoothly.

Best,   DennisT

I wouldn’t count on a regulator helping much. 

As for CG shift, the bladder could have more than a tank.  The bladder deflates starting at one end, like those long balloons that clowns use to make dachshund sculptures. Baby pacifiers have less CG shift, as do (maybe) modern F2D bladders.

My current stunt plane maintains the same CG throughout the flight, but it appears that you don’t like that solution.

Guys,
Since Paul Walker did the bomber with the four OS 15's with the pressure bladder fuel system and it worked, why hasn't that system been expanded to other single engine setups with the fuel over the CG? Seems this could even give IC a bit of an advantage with the ship getting lighter but no CG shift. What material was used for the bladder and who sells the regulator?

      Having watched two troubleshooting sessions on the bomber, I think it's far too complex for the very minimal advantage you would get. It might make for an interesting experiment, but I wouldn't expect to wind up with a competitive advantage.

     Brett

I know things in stunt change very slowly so this is in no way trying to revolutionize things but just kicking around some ideas. Howard's point about the way the bladder empties kind of back to front is something to consider. Mounting the bladder mounted along the wing spar might be a way around this. AM's steel tank with timed crankcase pressure could be interesting but would still need a large venturi and some type of pressure regulation. The other thing I thought of was one of the tanks that have the plastic bag inside the regular nylon R/C tank with crankcase pressure maybe with a one way check valve going to outside of the bag. Again we would need the larger venturi and some type of fuel pressure control to keep constant flow to the engine. One way I've seen used for some combat setups is a piece of tubing with something like a 0.020" inside diameter in the fuel line prior to the NVA, this acts like and orifice that has a controlling effect on the flow pressure. 

Best,    DennisT