Greetings,
I am a newbie builder that has a World Models Ultimate 40S. The airplane/firewall is set up for an inverted engine mount. I have a Super Tigre 51 that is going up front.
I;ve heard that mounting a 2 stroke glow engine inverted can cause a lot of problems. Any advice you can give to alleviate these problems such as special pumps, uniflow tank systems, etc. would be appreciated.
I'm trying to decide on whether to mount it inverted which would be easy since it's already set up for that or mount it sideways which will take a lot more work but if it eliminates the "inverted" engine problem I may do that.

the big problems with mounting an engine inverted can be solved by puting in a hotter glow plug with an idler bar to keep the fuel from quenching the coils and starting and tuning the plane inverted so that the engine is upright the first time so you can adjust everything too optimal so there will not be excessive fuel pouring into the glow plug. It usually runs good after that.

I've gotten heat in the past for speaking my mind on this. However, I feel there is no benefit in mounting a two stroke engine inverted, other then to get a lower needle valve to fuel tank level, where this is really necessary. To the contrary, it can and generally does make the engine difficult. Most of the really knowledgable engine people agree on this. Clarence Lee in particular feels it is only asking for flame outs and difficult running. Side mounting the engine is not difficult to do and makes for a reliable engine. All that is needed is re-drilling the mounting holes and filling in the old ones, not a difficult task.

People will tell you, if you do this, or that and change this, you can get a good running inverted engine. I say if you side mount, you don't need to pay any particular attention to anything to get a good running engine.

If your talking about inverted four strokes, these really do run o.k. upside down.

You can make a 2-stroke run inverted with a Cline Regulator.

Anything else is just a waste of time.

Best thing to do with that WM Ultimate is to side mount the engine.

I have an os .61 inverted on a p-51...starts fine/ idles fine
when i get to about half tank i notice the rpm's start to waver (leaning out)
so rather push my luck on a dead stick (plane falls like a brick) i land immediately
would a perry type pump be worth the bucks to keep constant fuel pressure?

pic's attached to show eng.

Should i go with an oscillating pump... or a regulated pump?

as long as you tune your inverted 2st engine correctly, not overly rich, they run great the biggest mistake is running to rich and having the fuel tank positioned incorrectly making sure the fuel lines line up with the carb nipple, and not to high, so the fuel siphons out of the carb.
the biggest mistake made is flipping a good running engine over and expecting it to run well without re-tuning seems like some 2st engines run better upside down better than others .
as for 4st engines all mine are inverted and they work great

I have several various sized engines which all run fine AS LONG AS YOU LOWER THE FUEL TANK. Don't need a regulator. If yo leave the tank in the stock position, you will have problems.

As mentioned, MAKE sure the tank is at the right elevation with the spray needle and it'll run great. I had the same concerns also, but following the help here I have absolutely no problems at all.

flynte

I have even put a loop in the fuel line to the carb to help against the siphoning effect. My inverted MVVS .25 does not take well to a prime. It will flood everytime. I just flip it by hand a time or two, with the lines disconnected or throttle at idle, to make sure it is not locked up with fuel before I put the starter to it. Also, be careful removing the glow ignitor, it is a different beast to get at under the plane. Maybe try a remote glow system.

Mount the engine sideways like it is designed for and you won't have to butcher the cowling up to make it fit. Also, if it is mounted sideways a Pitts style muffler will fit perfectly and exhaust through the bottom of the cowling.

Regards,
doubledee

i would never mount one inverted becaus the oil or leftover nitro that was not burned off will go down into the plug and it is really hard to get it running good again without changing the plug.

It seems that Ultimate 40S is designed for an inverted engine so presumably the tank is set in the right position (it's worthwhile checking though). The engine doesn't care which way up it is once it's running but you have to learn a slightly different way of priming it because you're trying to get fuel to run up hill from the carb and into the engine. Also, inverted engines need a bit more care in setting the idle mix to avoid any stumbling after prolonged idling. Properly set up you don't need pumps/regulators or any other complications.

dispite ALL the TALK I hear over the years, I have yet to see a TWO stroke run well inverted without some glow assist. last lad who showed up at field thought he could do it & was very frustrated. that includes lowering tanks , pressure "regulators ", idle bars etc. a hotter plug may cause other problems as well.there is also the danger of flooding and bending rods.IF & only IF well broken in you MIGHT get away with it but even then transition often suffers.

AMEN!

I have a bunch of these 40S Ultimates all now running just fine with inverted .46's.

Any problems I had turned out to be, not having the engine(s) tuned properly or fully broken in.

Now that I know how to set up the engine, I'm running quite a few inverted mount engines on other planes as well also w/o problems.

The Ultimate 40S' tank is not that far out of line that you have to worry about the stopper level.

The plane sits nose up when idling, which puts the stopper at the right level even when the engine is inverted.

If you are worried however you can merely invert the tank to lower the level a bit. (Adjust the fuel tubes too!).

Remember that if your engine doesn't seem to run inverted and you mount it upright or side mount, you haven't necessarily eliminated the problem this way. At low engine speeds in a tight bank or aerobatics, etc. you WILL be running the engine inverted and you may or will get deadsticks. Found this out the hardware after listening to some (mis)advice here about turning the engine on it's side... not needed.

It is best to tune the engine with 1/3 tank of fuel in an inverted position then work backwards to eliminate the problems. Make sure that you get consistent RPM's at low and high throttle speeds this way... then work on the mid range.

That is how I got mine running RELIABLY w/o having to resort to a hotter plug... which didn't really help.

Yup, nothing is needed.

The Ultimate sits "nose up" when idling, normally, as it is a tail dragger, so with the tank inverted the levels are fine.

However I haven't had any need of doing this, nor is priming problematic. It just takes a little longer to start with an electric starter.... a bit more cranking to get the fuel up before the engine kicks in.

With the needles properly set the fuel should NOT siphon back out that quickly at idle speeds.

If you open up the throttle it will siphon back though.

I dont care how much you "tune it " - thats the point. idle will be fine or top end fine. transition will not be so hot.your going to have TRANSITION PROBLEMS & YES you should go with glow assist..