In the just concluded flying season. I had a lot of trouble with an OS 75AX inverted on a Phoenix Topstar. We tried every possible config: with baffle, without baffle, rich setup, low end screw adjustment, high end needle adjustment, with nitro, without nitro etc. But we couldnt keep it running. Initially, it would cut-off in the hover but later on it began to cutoff even in level flight if it was run at 50% for one circuit. Cooling is not an issue as we were running it without cowl. When I was flying without nitro, I got it stabilised with the baffle installed but it couldnt sustain the hover and I had to try nitro to help out in that. All along I am using fuel with 20% normal castor.

Now for this season, we will be installing it at 90 deg. Some othere on my field with inverted engines also have had the same issues and they will also be doing the same.

My concern is that in my new reactor, if I put in a 2Stroke engine: the 55ax (I have a old workhorse that has never given me issues) I will have to install it at 180 or 225deg, I dont want any issues with it. What I want to know is, is it that the 2strokes cannot be mounted inverted? If so, I am better off going for a 4stroke OS FS 70surpassII / 70Alpha / 81alpha. If not, I would prefer to install the 55ax as its lower weight and fewer moving parts will give me a lighter wing loading that will be better for 3D.

I know that I have raised this issue before in the various forums but I am raising it again as I have not received a satisfactory answer to my query.

Ameyam

CL fliers use inverted engines all the time without issues, although they are confined to circles and no throttle. What I have found in CL (don't do that any more, but have a couple of friends that are among the best in the nation) is that they are very precise with every thing they do, especially in their engines and their tank set up in relation to engine position, something we R/C fliers need to pay a little more attention to perhaps. I also think that part of this comes from the fact that the C/L guys build their airplanes from kits or scratch (these two build from scratch) and we build ARF'S.

I've found that as critical as tank height is, it is much more critical with the engine inverted. If it is a little high, the engine is going to flood, at least that's been my experience with a Seagull PC-9. Got the tank positioned properly, leaned the engines high speed needle and low speed needle and never had a problem with the Irvine engine in the nose after that. It was a great flying model, and the engine was absolutely right on every time I flew it. I don't recall ever having a flame out after getting the tank positioned correctly. What I don't understand is why a model that is built for an inverted engine would have that flaw engineered and manufactured into the model to begin with, of course, this was from one of the early runs on this model. I have another waiting to be put together and they may have corrected that little problem, which was the only problem I ever had with it.

You've probably checked your fuel lines for the possibility that one has a pin hole in it (had that issue with the OS 160 with a Perry Pump in my GBY, with similar results), including the fuel lines in the tank and that the weighted pick-up line is not hung in the front of the tank. If you have not confirmed that, it would be something you might consider before you reposition the engine and or tank.

You might also consider a Perry Pump or Klein Regulator (if you have room) if the tank is too high or too low and you cannot reposition the tank without a major over hall.

"Experience is a hard teacher. She always gives the test first and the lesson some time later!"

I did replace all the external lines. But not the one inside the tank. I got the Topstar from my instructor second hand so I couldnt get the tank open. That is one consideration I will make this season before I fly the Topstar again.

With respect to the tank position, the tank centreline is almost at the same level as the carb, so I dont thinkthat it is the issue.

But can someone please answer whether the 2S engines can be mounted inverted?

Ameyam

Two strokes (4 strokes too) will run fine inverted if the rules of proper installation are followed. Centerline of tank slightly below the spraybar, tank not too big and positioned not too far behind the engine, fuel feed/fill/vent/pressure lines not kinked or leaking, muffler pressure used and engine tuned (not too lean) correctly. I have successfully run 2 stroke engines inverted in model airplanes since I started fooling with them some 40 years ago. If you are having problems, you are doing something wrong or have an engine with other problems.

Terry in LP

Presuming "spraybar" means inlet to the carb. I think I will try the 55AX inverted (or at 225 Deg when seen from infront) as recommended by the manual. Just to cutout other variables, I will use my old 55AX rather than a new one. For the Topstar though, I am thinking I will try out someone's 91FS on trial basis before I buy one for myself

Will keep posted about the results.

Regards
Ameyam

i agree with bubba if all is properly mounted tank, lines etc. all engines will run well in any position. Main things are no air leaks anywhere, tank position proper high and low speed set up, good glow plug. If contiue to have problem run on bench that will elemina te any problems with plane system.

Presuming the engine currently in the Topstar is OK, if you change engines without making sure the tank location and condition is correct, you'll be wasting your time. Hard to believe you couldn't open the fuel tank.

CR

Ameyam,
Don't presume anything. If you're not sure, ask.

The carb inlet is where your fuel line connects. The spraybar is in the middle of the carb throat. That's the tube you see going across, when you look down the carb at WOT.

If you can't get the carb properly adjusted, find some way to open the fuel tank, or buy another. Skipping something because it's too hard, or takes too long, will only extend the time it will take to get your aircraft flying reliably.

HTH,
EJ

Ok, hold on a minute, "presuming" was a soft way of asking so no issues.

Is the centreline of the spray bar the same as centreline of the crank? Please clarify

Old tank, so couldnt get it open. It is probably not in use for a couple of years or my instructor checked it before he gave me the plane. This is because, when both of us were struggling with the tuning, he never offered to change / check the tank. Very early in the course of the problem, I got a Dubro tank with the express objective of replacing the original. He didnt seem to keen to replace it. This dubro tank dosent fit in exactly so I didnt try too hard.

That reminds me, I have a very similar tank in my high winger. Will try it in my next attempt with the plane

Ameyam

I understand. I didn't want you to get confused, and create problems that didn't exist.

No. Open the carb throttle all the way. The tube you see going across the opening, is the spraybar. Ideally, this should be at the centerline of the fuel tank. Which is, usually but not always, the center of the stopper.

The centerline of the crank is the same as the prop shaft.

It would be a good idea to remove the old tank, if nothing more than to verify its condition, or check for irregularities.

Good idea, too. But, remember, just replacing parts may not tell you what the original problem was. Investigation can help educate.

Good luck, and let us know how you're progressing,
EJ

Does anyone have pictures of the fuel lines and clunk installation of a three line setup? I'd like to see some pictures of a fuel tank cut away and how the components are hooked up and the kind of safeties used to secure the fuel lines to the clunk, vent line, and the fuel fill line. I have this friend that doesn't believe me when I told him how to install his fuel tank components. First of all he's using a fuel line with a very thin side wall so his fuel line keeps splitting causing the clunk to come off. I gave him a piece of the fuel line that I use and when he put his clunk on it the first thing he said was it's a nice tight fit but the fuel line was to stiff so it wouldn't flop back and forth when going inverted. I said it would only take a little use and that it would become more flexible over time and after it's been in the fuel for a little while and not to worry. But he said he didn't want to use my fuel line and he would use the stuff he had been using. I tried to explain to him that the line he was using was not the right type of fuel line and if it were my plane I wouldn't ever use the line he was using. I don't think he's going to listen to me so I told him that I would pray for his plane. Then he said this,,if your fuel line becomes more flexible then it's reacting with the fuel and it's probably deterierating and melting away. So I finally figured that no matter what I said he was going to be right and I was going to be wrong. So I said,,well then use whatever you want because your going to anyway. There's just no arguing with him so I just gave up trying. Then I told him to at least use a tie wrap to safety the fule line to the clunk and the vent line and he said that using a tie wrap wouldn't work because it would eventually melt away. I told him that I had been using tie wraps for years and I never had a problem but he just won't listen. So you see what I'm up against? Please, if someone could post some pictures of a fuel tank that's been cut in half (cut away view) to show how the components are installed and how their secured, I would really appreciate it. And if you could list the name of the tank parts that would be great. We'll be using glow fuel.
Thanks and best regards,,,,Phil

I am having the same type of problem with my venu 40, i have a magnum xl70 4 stroke mounted inverted and it sits a good 3/4 below the tank and it floods out also. the venus really doesnt have any room in the front to move the tank at all. i was thinking maybe to wrap the feul line that goes to the carb, around the fuel tank a time or two to maybe help stop the siphoning. any ideals would be great, thank you.

make a loop on the fuel line, making the top of the loop higher than the carb.

I have yet to encounter a problem mounting a 2-stroke inverted. Following the common-sense related rules such as removing any fuel line issues is a must regardless of engine orientation. A tip that saves some of the flooding issues is making sure the throttle is completely closed when the engine is not running. Often, little priming is necessary. Bench running an engine inverted for initial set-up is a wise decision. If you cannot mount the engine inverted in your test stand try rotating the entire stand while the engine is running (I have a stand-alone test stand so this is not difficult for me).
The fuel tubing that comes with a new tank is of the 'thin-wall' type. Often, with smallish tanks, say up to around 12 oz., regular fuel tubing will not work effectively when used as a clunk line due to its rigidity.
An easy way to secure fuel lines to nipples, clunks, etcetera, is to simply cut a piece of regular fuel tubing about an 1/8" (3mm) long and gently push it over the end of closed forceps or needle nose pliers. Carefully open the implement's jaws enough to gently nudge the end of the fuel tubing you wish to secure inside the open jaws. Pull the thin piece of tubing off the jaws and onto the fuel line. Attach line and push the sleeve into a position such that it secures the fuel line onto fitting. I don't have any pics with me but it works great and is... FREE.

Actually. I already tried making a siphon when I was running without nitro. The idea was to prevent fuel flooding the engine when awaiting my turn to fly... and it worked... till I tried hovering. Anyway, I have mounted the engine at 270deg (clockwise when looking from infront). Earlier this was not possible as the stock muffler interfered with the firewall. But I recently obtained a Slimline muffler suitable for side mounting. Mounted the same on the engine today and ran it briefly. Earlier, I would always need an electric starter to start the engine if I tried starting it after a couple of weeks, even after choking to get fuel into the carb. But today after feeding a little direct into the carb and a couple of flicks with a saftey starter, it came back to life. Signs are good but I would prefer to keep my fingers crossed. The flying season is about to start here though I wont be able to take my 3D plane out for atleast another month. Also the fact that I didnt fly at all during the erratic monsoon means I am out of confidence so I will restart with my trainer or a tiger.. .did keep myself in touch through kit building and simulator practice but nothing equates to the real thing...

Will keep you informed, thanks

Ameyam