Guys,
I posted this question here to see if more flyers could add to the conversation. I am looking to build a ship that I intend to fly fast on long lines. I plan on running a 2-2-2 setup. I have done searches on pressure fuel systems for stunt and besides bladders not much information. So being around this hobby for some 40 plus years I remember using crankcase pressure into hard tanks for combat ships which need strong fuel supply. From what I've read the problem is that you still get a rich to lean run although not a bad as open venting. Seems that once pacifiers came along they provided even better fuel supply for combat and that kinda ended the crankcase pressure development.
Well, then we start using uniflow tanks with muffler pressure and that works pretty good. It still gets a little rich-lean in the stronger winds (not as bad as open uniflow or open vents) but I was looking for a little stronger system and thought since with uniflow it doesn't care how much pressure it only knows the pressure reference point so why not crankcase pressure into the uniflow. This would give higher pressure fuel delivery with the convenience of a hard tank and the steadiness of uniflow.
Having said this it all sounds logical but the proof is in the air. Things in stunt don't change much since if things work we don't have a lot of time to try different approaches. Not wanting to reinvent the wheel I put this out to the forum to see if others have tried this, how did it work and what would you advise or do different.
Best, DennisT
Crankcase pressure will work just fine with uniflow tanks.
It's still used locally with Super Tigre G15's in Vintage Combat models (.15's only) mostly for sports flying these days. The tanks have standard uniflow piping and the run is remarkably smooth and constant through the entire flight.
The backplate mounted pressure nipples (Brass K&S) are modified so that the hole is about .012". This seems to cure any of the ill effects noted above. Normally a piece of .012" c/l wire coated with carbon, paint etc is inserted into the standard pressure nipple along with some solder flux. A dob of electrical (60/40) solder is melted into the hole and the wire is pulled out before it can solidify. The same can be done with JB Weld replacing the solder.
Otherwise you can use the standard K&S pressure nipple and just crush down one end of a short length of 1/8" diameter aluminium, brass or copper tubing and insert it into the crankcase pressure (fuel tubing) line.
Some care is needed with refilling the tank. Most remove the pressure line from the tank and only reconnect it when ready to start. Otherwise crimping the pressure line prevents flooding through the backplate. I've never had much luck with "one-way-valves", they always seem to block up at the wrong time.
The older Enya glows had a pressure take of point opposite the inlet port of the shaft. It was for "timed pressure". The needle setting always seemed to be very sensitive to me when using it. Never tried closing the hole down to .012". Might have tamed the beast.
Good luck....