What's going on? Haven't seen a post here in some time. I'm hearing arteries creaking all around the country.

Need a question to get the blood flowing?

What about "Uniflow fuel tanks"?

Is there any proof that they do any better then conventional wedge style tanks?
I would like to see some pictures and an explaination of how they work and why
there better, or just different.

I understand the use of pressurizing a tank to get constant flow to the carb.
How does a uniflow better that?

Happy Holloween,
Bruce Bennett

I'll bite, even though I've not yet used one. (I have seen [and heard] them used).

A pressurized tank, although it improves fuel flow, generally, does little to even out the fuel feed changes that occur during the process of emptying the tank. I'll try to explain. If, with a full, non pressurized, two inch high tank the fuel is one inch above the carb, you have a fuel "head" pressure of one inch of fuel pressure. As the same tank nears empty, the head will be closer to one inch negative pressure (assuming the tank is centered at the carb level). That means a difference of 2 inches of fuel pressure between full and empty.

Pressurizing that same tank with, for example, 10 inches of fuel pressure, would mean that the full tank would feed the carb at 11 inches, and the near empty tank head pressure would be 9 inches. Still a difference of 2 inches between full and empty.

Now with a uniflow set-up, the suction needed to draw fuel from the tank decreases as the tank empties, effectively evening out the difference between full and empty. This is how it works: The vent line--the opening through which air comes into the tank to take the place of the fuel that is being taken out--is directed to the bottom of the tank, as close to the fuel pick-up as possible (without causing the pick-up to suck air). So, the incoming air must come in with at least 2 inches of pressure to displace the fuel at the bottom of our 2 inch high full tank. So now, in order to draw fuel from the full tank, the carb must draw the fuel with one inch of suction, or, to put it another way, the head pressure at the carb is now 1 inch less 2 inches = negative 1 inch. A half full tank will have a head pressure of 0 inches less 1 inch = negative one inch, and the near empty tank will have a head pressure of negative 1 inch less 0 inches = negative one inch. So, the fuel draw will now be consistent for the entire fuel run.

It took me a little while to wrap my mind around this concept, but now that I got it, it makes a lot of sense. Hopefully my explanation makes sense, too.

Phil

Bruce,

I'm not sure a uniflow will buy you much if you are using pressure.

A uniflow helps compensate for the engine's ability to draw fuel by evening out the pressure seen by the venturi.

George

Edit: There is an easy way to check:

Install a uniflow tank using a standard setup. Try it with the uniflow supplying only atmospheric pressure, then add muffler pressure to the uniflow and try it again.

Next you plug the uniflow vent and open the fill or overflow to atmosphere and try it. Now add muffler pressure to the open tube and try again.

Of course you have to establish your needle setting for each combo so it may take several flights on each to establish how the engine runs at takeoff and just before it quits.

You should now have your answers..without speculation.