Following is a response from Ken Cook back in 2012 on uniflow tanks. The point he makes here as we know, a properly set up uniflow tank will provide an even engine run by creating a constant tank pressure. Except of course at the very end. But in the last paragraph he goes on to say rotating the cap enables us to change the engine run. By doing so doesn't this impact the gravitational static liquid head (L) we see when inverting the model or tipping up the nose similar to a standard vented tank. This "head change" of course is completely unrelated to the position of the uniflow line but more so the position of the tank outlet relative to the spray bar. Aren't we seeing two different conditions here?
Steve
Unfilow tanks have a additional pipe which travels alongside of the fuel pickup. It stops about 5/16" from the rear of the pickup. Uniflow tanks MUST BE FILLED through the uniflow pipe or else when the fuel level rises in the tank it will exit the feed pipe resulting in a flooding the engine. The unfilow pipe provides a magical quality to the engine run. The uniflow pipe itself exits the tank and is pointed directly into the wind. This pipe stays uncapped and the other pipes,(filler and overflow are capped). Using unfilow on profiles presents vibration to the tank and also turbulent air over the cylinder now in front of the tank. Getting your unfilow pipe extended to clean air (typically the inboard side of the plane) is important by adding flexible tubing and placing a piece of hard tubing mounted out of the way of obstructions is importantl A standard vented tank, and we can use the wedge that most are familiar with. As the tank is full it has a lot of head pressure. The engine run is rich, as the tank empties, the head pressure is less but the engine leans and continues to lean throughout the run until empty which usually unless properly set, results in a screaming lean run cutting in and out all the to the end. This type of run maybe ok for the sport flyer, but when flying stunt, this isn't ideal. We like the smoothest steadiest run we can achieve with a clean cut off at the end.
Uniflow tanks provide terrfic runs but they also lean out slightly just not to the level a standard vented tank does.
If the plane is vibrating and the fuel is foaming, UNIFLOW WILL NOT WORK. Uniflow generally needs to be set with the engine on the ground rich, the uniflow pipe is bent at a 90 deg angle into the atmosphere and as the air pressure increases into the pipe the engine leans out usually settling into a nice 4 stroke on the verge of a 2. Sounds great I bet, I can't ever get it to work for me and this is usually on profiles which are subject to vibrations. Sometimes the uniflow pipe needs to be necked down to work properly by inserting a small piece of tubing over the 1/8" tubing. Armor All in the fuel sometimes and most of the time works to settle down the fuel foaming internally.
I like uniflow tanks for 3 reasons, I can use it as a uniflow tank. If uniflow isn't successfully working, I can cap the uniflow and overflow leaving the fill vent open and it now is a standard vented tank. I can also cap the uniflow and overflow running muffler pressure to the fill making it a standard tank on muffler pressure. It just gives you many options.
I personally hook my muffler pressure directly to the uniflow to what I refer to as uniflow on muffler pressure which seems to work the best for me. I've seen many guys use the uniflow tanks just like I stated above and have perfect results. The idea of uniflow is just to enable the engine to run at a constant speed without leaning out other than when required which would be pointing the nose up.
Unfilow has a very unique characteristic, the uniflow pipe is what dictates your tank height and NOT your fuel pickup like a standard tank.
This can be extremely helpful in setting your tank height on a plastic tank as all you need to do is loosen the screw on the front and rotate the rubber stopper and piping and this will change your engine run. Metal tanks need to be shimmed up or down. I make adjustable bracketing for my hard tanks. I make a piece of ply with slotted holes and I attach the hard tank to the 1/8" ply with nylon zip ties. Screws then go into to the slotted holes of the ply and are tightened to affix them at that height on the plane. If needed, I loosen the screws and slide the tank up or down if needed.
Topic: Plastic clunk tank uniflow set up (Read 5038 times)
