Problems with Inverted .40 FX

Good Evening. I have a newly finished Tower Hobbies Voyager with an O.S. .40 FX. This is my first time flying a plane with an inverted engine. The engine has run fine in my previous planes (with the engine upright), but I can't seem to keep the engine running on this plane. A friend at my field suggested I try starting the engine with the plane inverted. This seems to work, but when I then put the plane upright, the engine stops, and fuel drips out of the carburetor. Eventually, when I try to start the engine, the engine will run for a second or two, then suddenly stop and freeze. This seems to suggest flooding in the engine. I wonder if the engine/tank setup is the culprit here. I have given some thought to re-orienting the engine to an upright position, but I would have to completely modify the plane to make that work. Any suggestions? I'd really like to maiden this plane soon.

Thanks, Harry Sanchez

Reply to
Harry Sanchez
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Where is the carb vs the tank centerline? The last OS engine I used was intended to be used with a pressurized tank.

Reply to

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

Inverted engines usually require modifying the airframe. Typically, the fuel tank is too high.

Check the height of the fuel output line AT THE STOPPER on the tank in relation to the SPRAY BAR in the carb. It should be within 1/4" with even or slightly below the spray bar is best.

To get this height you will most likely have to hog out the tank supports in the fuselage.

You also want to make sure you have a solid connection for the pressure line from the muffler or backplate to the tank.

For inverted installations I use a 3 line system for the tank, AND a remote glow ignitor. The remote glow ignitor saves the fingers. The other thing for inverted engines is to use the glow ignitor from your power panel. It will provide more juice to the glow plug than the "hot shot" glow ignitors.

For future reference try to install the engine sideways, or if that is not possible, try to angle the engine as much as possible to minimize fuel pooling in the head and cooling/shorting the glow plug.

Hope this helps.

Reply to
Ted Campanelli

Hi Harry, Sounds like your fuel tank is mounted too low. Is it possible to raise it?

Reply to
Ed Forsythe

In addition to what Ted said, a fast start at a fix is to lean the main needle out 1/2 turn and the idle needle 1/4 turn. In short you will have to retune both ends of the carburetor when you flip an engine orientation. Good luck

Reply to

I was thinking to high? I had a Razzle with inverted engine. sometimes hard to start but was ok after, sometimes started it on the wing tip. mk

Reply to

Oops - My bad! You're correct mk - I got crossed up and pulled instead of pushed ;-) if the tank is too high it's possible to create a siphon effect and the fuel will flow freely into the carb. when you invert the bird the too high tank position becomes a low position eliminating the flooding.

Reply to
Ed Forsythe

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