Mounting upside down two strokes

[Paul Williams]

hi, can some one help? I have mounted an OS 40 upside down in my uno watt. I am have a nightmare trying to get it to run properly. Although the tank is as low as possible I am still getting a syphon effect once the engine has run I am constantly ajusting the mixture and dead sticks are common. The engine ran fine with the cylinder up in the last plane. Any thoughts?

[flytilbroke]

I have had two Models fitted with Irvines with similar symptom. I got them to run well from a FAST tickover to full throttle by setting up as normal for full throttle and leaning the low end out a bit. I found that a low tickover for more than half a minute caused them to stop, I believe the cause was pooling of oil in the glowplug, Hense the fast tickover to help void the oil. I now find them reliable as long as trim set for the fast tickover, pull trim down for landing though. There are ways to allow the fuel feed to be "pinched " to prevent syphoning when the model is static, I use forceps to clamp the feed tube

[Alan B]

Hi Paul - I had the same problem as flytilbroke and had the same solution. That was an inverted Irvine engine as well.  However when I was at that nats I picked up a couple of   Model Technics glow plugs that are supposed to be designed for inverted engines and inverted flying 5% - 25% nitro range.  I personally had never heard of or had seen them before.

 

 I replaced the fitted OS plug with one of those and the engine runs far better and slower bottom end and no dead sticks. Apparently they are designed to cure the oil pooling effect.

 

works for me - it might help you.

 

Al

[Paul Williams]

Thanks guys I will sourse one of them glows and try again but it don,t cure the syphon which I feel I can't live with. I may order another cowel and live with it ugly but reliable.

thanks again for your time

 

[Flanker .]

Oil pooling effect ????!!!!  No. A model engine should run fine inverted. I suspect a fueling problem.  You will need a model stand. Set the tank up as normal, ie spray bar in middle of tank centre. Use a fuel valve so that the supply is cut to the motor when you fill. You should NEVER touch the mixture once set, it will NEVER solve anything. So put the motor in a test stand and set the mixture correctly FIRST. Once the engine throttles cleanly re fit it in the model. Fill the tank with the model right way up,so that fuel does not go down the breather and pressure tubes until the tank is full.  ALWAYS START the motor with model inverted and let it settle. Select a fast tick over and gently turn the plane over to its flying position if you get a cut roll over and re start. I have used inverted engines for years with NO trouble. READ the WOO article in this months SPECIAL it is ALL TRUE. I NEVER touch my mixture, and I have not touched the main needle for months. IF these things need to be endlessly re adjusted then you motor is finished. Mud in the carb is a prime cause. See my notes on air filters elsewhere. The mud wares away the rotary valve and cause a variable mixture state that no amount of fiddling will fix. I have just gone out and flown my inverted engined Champ today after a THREE MONTH lay off. WITH the cylinder stored down. The engine cleared its oil in two minutes of flick burrrt  and  then ran like a train and I TOUCHED NO NEEDLES! Really.

 This is important. The engine had not run for 3 months so I knew it would have oil in it. It was slightly hydro locked with fresh fuel. I turned it over by hand and tipped excess muck out of the exhaust, and then flicked it until it ran.It fired all the time but did not pick up. It is at this point that so many folks start twiddling the needle. Don't do it. If it was ok last time and you have not changed fuel, then it is still ok this time. If it does need adjusting every flight then your motor has a problem. I KNEW that it was ok last time so I just patiently asked it to start untill it did.

If Fuel is pouring out then something is BADLY amiss.

A good trick is to mount your fill valve at around top of the  tank hight. That helps to stop drips.

 

Good luck., and pm me if you need more help. Go well, F

 

 

 

Edited By Flanker . on 02/10/2009 13:24:56

[Misha]

I have some problems like this. engine (Saito 72) is in inverted position.

Every time it has to be set and again it won't run ok. I think problem is because 

tank is probably 1/2" higher than carburetor. I cant move either motor or tank.

 

Any suggestions?

 

Tthank you in advance

[Paul Williams]

The carb is to low when the motor is inverted. I cant get the tank low enough. So its syphoning and flooding. I have remounted the motor and all is fine but I have to live with a cylinder sticking up through the cowel !! Thanks for your input

[Ernie]

Hi guys,

Just Engines sell an onboard gloplug energiser, that provides power to the plug, just as it is about to go out

 

ernie

[BB]

Have you got the link for that energiser Ernie, I can't find it on their web page.

 

BB

[Peter Miller]

Funny, I never any trouble with engines in any position, especially inverted. Tank top 3/8" above the spraybar.

 

When an engine is inverted the carb is pointing downward so any fuel siphoning out pours OUT of the carb, not into the engine.

[Ernie]

Hi BasBig, How's algie?

try this http://www.justengines.unseen.org/acatalog/On_Board_Glow.html

sorry timbo, I'll do it correctly next time, when I have a minute to suss it out

ernie

[Tony Campbell]

Sorry to dig up an old post but the comments made above regarding turning the plane inverted to start it is completely unneccessary.  If the engine is correctly primed, ie, not over-primed then it will start happily regardless if it is upside down, sideways on or back to front.  However, the comment regarding oil pooling round the glowplug does carry some merit, although it is most likely to be normal fuel mix rather than just oil. This only applies to start up however and all model engines can (notice i said can) get a bit unhappy if left to idle too long, this is generally caused by the plug cooling down past its optimum.  I also applaude the comments made regarding not twiddling the needle........ wish I had a quid for everytime I've seen someone doing that when it wasn't needed......... normally followed by a deadstick and long retrieval.

One tip i had from just engines, was to fit a fourstroke plug in an inverted 2 stroke to help with engine cuts at tick over. Care had to be taken with piston to plug clearance, using 2 plug washers if needed. It certainly worked though! 

[Paul Williams]

Thanks Tony,

I ended up remounting the engine  cylinder up. This solved all problems and its been a happy bunny since. Cost me another cowel though Grrrrrr

I take your points on board though and will review them next build.

 

Thanks

 

Paul

[Martin Harris - Moderator]

Wouldn't surprise me if a lot of these inverted engine problems in flight are due to overheating.  Most inverted installlations put the cylinder nicely into the middle of the cowling and many people just don't grasp the principle of getting air to flow over the cylinder and head and, most importantly, then find an easy way out.

 

You wouldn't believe how many people reckoned my combat Hellcats would overheat when the only hole in the front of the cowling (other than a hole big enough for the prop driver) was a slot about 1/4" x 3/4" direcly in front of the cylinder - the exit hole was around and particularly to the rear of the head (whole engine enclosed by the cowling) with a small lip formed in front of the hole to create an area of suction. The art is making the air flow where it's needed and not finding another easier way...

[Doug Ireland]

I'm going to agree with Peter M, I've never had a problem starting/running engines in any position either.

[Peter Miller]

Martin is right, the art of cooling an engine is neglected by so many.

 

The air exit must be much gigger than the inlet. Also it helps to force the air though the fins, not just round them.

 

You see engines in big radial cowls with a small narrow outlet round the fuuselage at the rear. The answer is a ply baffle roughtly on the centreline of the engine and close to the engine. You can use this baffle to mount the dummy cylinders.

 

Another good example is the typical cowl on a control line speed model. It as a tiny inlet, slightyl larger out let. The cowl almost touches the fins and the whole duct is shaped like a venturi. You get a big negine turning at very high rpm on very high norto content fuel without over heating.

 

On the subject of plugs. I use Taylor Standard Long Reach on every engine. never have any problems. They are also much cheaper than other plugs.