buzzard bait

This is old news, but a lot of people have missed it. I have an ancient Saito 40 (looks identical to the old 45) which has no muffler and therefore no muffler pressure (there is a place on the exhaust pipe to hook up a tank line, but hooking up to it would not give me good runs). It ran well, but it would lean out a lot in the course of a flight, so much so that I had to start pretty rich to get a decent flight.

I finally set up the tank as a uniflow system and I just cannot believe how well it works! I'm now getting absolutely consistent 20 minute flights on a 6 ounce tank and I can set the needle on the ground for maximum power with no leaning out during flight at all. It is just dead reliable down to the last drop of fuel.

It requires a three line set up with two clunks. One goes to the fuel as usual, and the other is vented in my case, or attached to the muffler if you have one with a nipple. You can fuel through this latter tube. The vent at the top of the tank has to be plugged after you fuel up, before running the engine. It has to be open for fueling. I use a fuel dot. So it is used the same way as any other three line system, but the plumbing is different inside.

The link I used has been posted many times, but here it again...kudos to the guy who did this site:

http://www.fraserker.com/heli/uniflo...flow_works.htm

If you have an older engine with no muffler pressure available, or if you have muffler pressure but still can't get even runs start to finish, this is the cat's meow.

Jim

freakingfast

My Feedback: (3)

Uni-Flows are are great aren't they?
Here's the variation I use.

http://www.rcuniverse.com/forum/fb.asp?m=9045226

buzzard bait

Nice picture! I'm not sure I understand the reason for the check valves. It looks like it eliminates the need to plug the top vent after fueling, correct? Does it do something more than that?

Also, the use of a fuel filter as the clunk for the fuel line (the Dubro I think?) is one of the nice things about any three line system, and I plan to do that too next time. But I figure that eliminates the need for a fuel filter between the tank and the engine, right? Looks like you've got two filters. Not that it's such a bad thing...

Anyone using a three line system can convert simply with the addition of one clunk. Get a Dubro scintered bronze pick up and use the stock clunk for the other one. Why doesn't everybody do this?

Thanks for the response...good to hear from someone else who is enjoying this brilliant idea.

Jim

downunder

It's good to know that the RC guys are finally catching on to Uniflow . I just had to say that but in CL stunt we can get away with a slightly simpler system using a fixed Uniflow tube against the outside wall of the tank because, in flight, the outside wall is effectively the bottom of the tank due to centrifugal force.

Sport_Pilot

On a uniflow some of the muffler pressure remains in the tank and the fuel pressure can cause a short richness, also a small amount of fuel can be pushed back into the muffler depending on line length. His method allows the residual pressure to vent back into the muffler, but the issue of dumping fuel will be worse when inverted.

freakingfast

My Feedback: (3)

Pretty much what Sportpilot said, and yes Sport, it could momentarily dump fuel into the muffler AND go rich, but only if you had chopped throttle and be inverted, but no worse than a standard Uni-flow.


Yes buzzerd, you can use any clunk, but I love that OS clunk for it's ability to eliminate bubbles in the line, draw the tank dry and good weight in a compact size, high flow rate (at least 3oz @minute ). I hate the price! but that's OS for ya. I don't know what the flow rate is on the Dubro, but it has more restriction at 2.7 oz a minute so I couldn't use it in one of my thirsty engines. It's probably good for 55 two and 82 four stroke normal engines, but if you lack needle sensitivity you had before, you know you have a line restriction and that clunk is the culprit.
The reason for the two filters is that I fill between them, that way any crud that I may introduce during fueling gets trapped between them and not between the clunk and carb.

buzzard bait

Interesting posts, thanks guys.

Yeah, Downunder, I actually remember this system from about 45 years ago. For awhile you could even buy uniflow tanks all soldered up, I believe.

Jim