Inverted engines, need advice.
 

I'm getting my first in-cowl inverted engines set up plane close to ready. I've been told that inverted 2 strokes can be a real problem. It's been suggested to start the motor with the plane upside down. Sounds scary to me. I guess it could be secured in the cradle of my flight box. Also reliable slow throttle and idle can be a problem. Really not crazy about too many dead sticks. Anyone had some experience with this set up? Would specific glow plugs or fuel help? Rich/lean setings? The motor is a GMS .47 but may swithch to a OS >46FX. Any help would be appreciated.

Inverted engines, need advice.
 

Inverted 2 strokes are no problem at all. If your model was designed for an inverted engine then the tank height should be very close to what's needed (centre of the tank level with the centre of the carb). The idle mixture has to be set so that it's very close to being exact, you can't get away with it being near enough (but we all try to set them exact don't we? :D ). Apart from that you'll need to develop a different technique for priming, after all, you're now trying to get the fuel to run uphill from the carb. Before you hit it with the electric starter always flip the prop a couple of times by hand to make sure it doesn't have a hydraulic lock.

Inverted engines, need advice.
 

Make sure your fuel tank is correct. When an engine is inverted the carb is bellow the fuel tank which can cause flooding. Alot of engine problems can be traced back to impoper tank installation/positioning. I was allways taught that the fuel tank should be positioned so that the fuel line was inline with the fuel connection (nipple) on the carb. Run it on the ground at different throtle setting and test it.

Inverted engines, need advice.
 

The only real problem you might have is a rough idle like you said. It seems that with the fuel falling on the plug, it wants to cool it off a lot more. Make sure the idle is set perfectly as downunder said, and have fun. If you have the weight/space to spare, you can look into an on-board glow driver, or make one on your own. With some creativity, you can make it light when the throttle is at idle.

Inverted engines, need advice.
 

Don't worry, even at idle speed, the piston is moving way too fast for the fuel to "fall" to the plug.

Inverted engines, need advice.
 

An inverting a 2-stroke can make it easier to get a hydraulic lock situation when using an electric starter. This can lead to engine damage, usually a bent or broken rod, as I understand it. But I've honestly never seen it actually happen.

It can be harder to start, since primeing can be harder, and any excess fuel and oil can have a tendancy to stay there.

On the "plus" side, if your tank is mounted too high and you get syphon action, it won't fill your engine with fuel, it will all train out the carb opening and on to the ground instead. However, with an upright engine, the syphoning usually stops when the engine fills. It's possible to empty an entire tank on to the ground with an inverted engine (and even some side mounted engines).

Once the engine is running and warmed up, I've never noticed a difference.