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General control line discussion => Open Forum => Topic started by: Dennis Moritz on February 03, 2009, 10:45:15 AM
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Dan Banjok has been experimenting with Tettra tank configurations in order to provide a reliable engine run on a profile. Profiles, as many of us have found, are prone to unpredictable vibration syndromes. Dan's reasoning is that a bladder tank like the Tettra can eliminate air bubbles in the fuel, a major cause of erratic engine runs. Initially Dan plumbed the tank as specified in the instructions. The result was a predictable engine run followed by a lean run of 8 to 10 laps. Inspecting the tank after flights, it was apparent that the bladder didn't collapse evenly, trapping fuel. Attempts to compensate for this didn't work. The pickup was moved around, muffler pressure and even crankcase pressure, didn't get the bladder to compress fully. Dan reasoned that towards the end of the engine run, the bladder created a vacuum, causing the problem.
Dan's solution was to reverse the Tettra setup. He plumbed the tank so that fuel was stored exterior to the bladder, in the hard tank. Before filling the hard tank, the air is sucked out of the bladder and the bladder is temporarily capped. Fuel is added to the hard tank until it is completely filled, all air released through the overflow. The overflow is then capped and the inlet to the bladder is uncapped and connected to muffler pressure. As the fuel is drawn from the tank during the flight the bladder expands to occupy the space previously occupied by the fuel. No air bubbles. Consistent pressure on the fuel throughout the flight. So far this version is working. Very nice 2-4 with a sweet running LA46. It goes lean two laps before shut off.
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neat idea ! y1
The most simple fix for bubbles tho - is to use a sintered brass clunk (filter) as the pickup.... works every time!