is it ok to mount the engine upside down, it seems that that is the only practical way for it to fit, if i mount it rightside up it sticks out way to much and doesnt fit inside the cowling, is there any disadvantages to doing this or what

Inverted is fine. You will probably find your plane is designe for an inverted engine.... you never know.

There are some down-sides to inverted install (no pun intended...).
Setting the idle adjustment for the engine is (slightly) more tricky, and you may have problems with an overly-rich enine "dowsing" the glow plug (the glow stops glowing, the engine stops...). The right idle setting will stop this from happening.
Getting the tank installed to be the same height as the carb may be a challenge as well.

Other than that, there are no significant mechanical differences. All other differences are aesthetic and practical.

gus

I've got two 25 size planes flying right now. Looking from the front, one engine is mounted with the cylinder at about 7:30. The other engine cylinder points straight down. Both idle with no problem. In fact, the one straight down first had a Saito .45, then an OS 25FSR, and now an OS 32FSR. All idled great once set.

One trick is to spend time adjusting the engine while the cowl is off. Start it up and taxi it around for a while. Once the idle works reliably while taxiing, iIf the flying characteristics will be ok, go ahead and fly without the cowl. This will make it much easier to adjust the low speed needle. Note, since most low speed settings require the use of a screw driver very close to the prop, you should always shut the engine off before changing this setting.

Hope this helps.

If you are a true beginner, I wouldn't recommend an inverted mount. I would say that it is much much more difficult to run an engine that is upside down than it is to do it in any other appreciable angle.

For beginners building an ARF for the first time, I would recommend a normal (right side up) mount. If that is completely not acceptable, go with the sidewinder. I had an O.S. 32SX that idled and flew fine inverted. My Towerhobbies 75 ran terribly inverted. Deadsticked all the time.

That's just my 2 cents.

Hi!
As "Fourstroke" said.....If you are a rank beginner inverted engines are not for you! That simple!
Inverted engine always will provide much more trouble than an "ordinary" set-up will. It is hard to reach the glowplug, hard to disconnect the glowplug without sticking ones fingers in the prop and sometimes the engine could have difficulties with idling and throttling.
I always try to mount my engines tilted to the left...with the right side up for easy reach to the carb needle and fuellines. One more benefit with this installation is that you get the engine axle higher up which benefits fueltank installation and prop to ground clearance.
Regards!
Jan K
Sweden

jaka - is that a header tank or the real thing? btw, thanks for the vote of confidence.

Hi!
That is the (only) tank I use in my Great Planes GEE BEE R-2. It's a Tettra "Bubbleless" heli tank (450cc).
Regards!
Jan K
Sweden

The only thing I can add is this. Use an idlebar glow plug. That will help with fuel puddling in the plug. As others have stated. If the engine is set up right there is no real problems.

Mark Shuman