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Engine basics => Engine set up tips => Topic started by: FLOYD CARTER on June 30, 2009, 10:39:25 AM
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I usually have zero problems with fuel tanks, but now I have one with a bad attitude. It's a commercial 5 oz. metal wedge design (inside fuselage) with uni-flow setup. Non-muffler pressure. Runs fine, but it takes about 10 laps for the engine to finally quit, after stopping/starting multiple times. (The usual cut-off loop doesn't work).
Question: where is the best place for the uni-flo tube to terminate? I normally put it about 1/4" ahead of the pickup tube and soldered to it. I suspect something is wrong with the location of the uhniflo tube.
Floyd
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I have built uniflow tanks with the uniflow anywhere from the front of the tank to where yours is. All worked well. Not running pressure, the run should go rich when the uniflow is uncovered, then go lean as bubbles start to get in the fuel line. I would try cutting off the end of the uniflow and moving it another 1/4 inch forward as the first easiest thing to do. As long as the uniflow is in fuel, no way you can kill the engine.
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The right solution to getting a clean cutoff is to cant the tank inside the body so the rear end is outboard of the front end. This makes the engine run strong until the pickup opens to air and the run stops clean. If the tank is parallel to the fuse centerline, the fuel will draw down until the pickup is uncovered, sputter, and the line drag makes the nose yaw in. The fuel runs back, re covers up the pickup and the engine runs full song for about a few yards, and the cycle repeats. Very awkward. If fuse layout prohibits a canted tank, try cutting the end off the pickup at a shallow, long bevel. Its not as good as canting the tank, but should give some improvement. Tom H.
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Tom's right, I've decided to start building fuselages wider just to be sure I have enough room to play with the tank.
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Getting the plane to fly tangent to the circle will help a ton. If you have rudder or engine offset, decrease it. Then try moving the LO's forward. Sight down the flap hingeline in flight to check for yaw. Temporary targets can be added to assist in this task. You should receive better line tension overhead as a bonus. Don't forget to report back! D>K Steve