Loc: Central Pa. USA
08-25-03 03:41 AM - Post#25194
In response to RC Man1
Hello, This isn't my article. It seemed correct, so I copied as a reference. I've seen pictures and could probably locate a diagram if you don't find something from someone else. Later, Jon
~~~~~~~~~~~~~~~~~~~ Uniflow 101 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3 different things affect fuel pressure...
Gravity, muffler pressure, atmospheric pressure (compared to the lower pressure in the carb needle)
If you use uniflow connected to a muffler with it feeding into a clunk at the bottom of the tank then the muffler pressure has to battle against the weight of fuel and the atmospheric pressure on the outside of the tank...
This means that you get a uniform pressure all the way down the tank no matter what attitude you helicopter is at... (although it will richen when the engine switches to header tank only giving you a good warning to land)....
If you are not using muffler pressure then you are running a merely vented system fed by gravity which means the fuel pressure will change from upright to inverted unless the fuel is always exactly at carb height.
When running a uniflow setup with muffler pressure to the second clunk you have to adjust your needles so that the engine is correct for the overall lower fuel pressure... it takes careful tuning, but because the engine will not lean as the tank empties you can generally get it done with one tank of fuel.... and some different flight tests...
Connecting the fuel lines... muffler line w/fuel shutoff, goes to newly installed uniflow line (with clunk)
vent is plugged
original line from tank w/header tank goes to header tank. from header
tank, line goes to carburator w/a fuel shutoff. Any vent in header
needs to be plugged.
original line from tank w/out header tank goes to carburator with a fuel shutoff installed.
The downside of uniflow is that with a quick transition from full throttle to idle you can get a small amount of fuel to return up the muffler clunk into the tuned pipe, typically this can be when switching from idle up to normal on the ground, however it is minimal as the fuel pressure is lower overall so doesnt cause a problem (hitting throttle hold could do the same but also it will be minimal back flow)