Tettra Bubbleless Tanks

Say, you guys go to Central Hobbies web site and look at the above fuel tanks and tell me what you think. I had visions of the uniflow vent or muffler pressure to the air space around the bladder. Should eliminate foaming, at least. While there, check out the CF pushrods and titanium ends. I bought some and if you haven't seen them, they are the slickest thing out there.

I just went and looked, but the pics wouldn't load, so I guess their website must be partly busted. It sounds like the "Jett" tank that Doug Moon was going to use in his "B&V 170" for profile stunt. He said they work slick. Muffler pressure is pumped into the tank with the bladder seperating the fuel from the pressure. Seems sensible, if you have muffler pressure option, and is it enough pressure to feed a really big venturi? Would it work with crankcase pressure? It's neat to see these new technologies, but we need to try all of them out and spread the word on how they work for our use. Steve

Muffler pressure is not enough to feed a "really big" venturi. It will help if your venturi size is marginal, but if you take the muffler tube and put it in a jar of water, the bubbles will cease to exit after about 6 inches of depth. So that is about half a pound of additional pressure compared to about 15 pounds of atmospheric pressure. I don't know how crankcase pressure compares, but that will lose some crankcase compression which does something else to your engine. An exterior vibrating or mechanical pump would probably be better if you need more pressure, but then you should probably just go to a stretched bladder as the combat boys do. (Or, maybe, go back to a smaller venturi?)

...the bubbles will cease to
>exit after about 6 inches
>of depth. So that
>is about half a pound
>of additional pressure compared to
>about 15 pounds of atmospheric
>pressure...

Leonard :-

I hate to contradict you but - 6" of water is actually a bit less than one quarter of a pound per square inch (1 psi = 27.71 in. water. Also, by sticking your tube in a glass of water you are measuring "gauge pressure" which is additive to the "about 15 pounds" (14.7) of atmospheric pressure.

JW

I realize it is additive. I was thinking it was a half pound, but if it is only a quarter pound it just reinforces my point that the additional pressure caused by muffler pressure does not do a great deal to offset having too large of a venturi. I have found the engine runs to be virtually the same (power wise) although muffler pressure can tend to smooth it out a little and eliminates uneven runs caused by siphoning or wind effects in the inlet to the tank. There is definitely a difference in needle setting, however, and, if the pressure line comes off (or becomes plugged) there will be a drastic change in the engine run from that point on.

"To use muffler pressure or not to use muffler pressure" is one of those ongoing debates with each side having its proponents. Just don't look on it as a means of drastically increasing the size of your venturi.

Guys,

No muffler pressure for me - I learned -- The HARD way!

RCJ

I had a muffler (stock muffler) break off on a Fox 40 once while using muffler pressure. The engine screamed lean and ran for 15 minutes. That was the only disaster we have experienced using muffler pressure, so still recommend it on most of our stuff. Just don't recommend a stock Fox muffler. They break.

Not sure exactly how we got onto large venturis-guess I was wondering if anyone had tried the bladder type tank with a uniflow type vent to the space surrounding the bladder.

OH, wait, I see, now. This is not a bladder of the combat sort-it's a soft bladder inside a plastic fuel tank that collapses as the fuel burns off.

More akin to the old Jim Walker balloon tank, but with an outer pressure vessel, I am just speculating as to how it might work for various CL uses. Keeping air out of the fuel could not hurt, that's for sure. As for a "Uniflow type inlet", since there is nothing except "ram air induction", which would change with wind/rotation, why not just vent to atmosphere without ram induction? Then you don't need the heavy outer pressure vessel, and you're right back to the Jim Walker tank! I thought you were referring to something you found at their website, my mistake. Found the ad in the latest MA. Kinda pricey, and not a lot of info. Check your local hobby shop so you can look & read before you buy, I guess Steve