I have just recently completed building the Great Planes Venus 40 (ARF) which utilizes an inverted engine. I am using the OS 46FX, which when in the inverted position has the carb considerably lower than the fuel tank outlet. The fuel tank is being filled with a remote fueler mounted low and behind the firewall. The problem I have is that the engine runs extremely rich, that is if I can get it started before the plug fouls due to the siphoning action of the fuel supply. Fuel will run out of the carb when the engine is not operating. Does anyone have any good ideas as to how to solve the flooding problem, or should I just turn the engine right side up and be done with it?

To eliminate the flooding of my inverted engine on a UCD I just use a large paper clip on the fuel line after landing. If you use a fuel valve most will close the flow of fuel to the carb when in use. Just use another valve plug with a small piece of fuel tubing attached and blocked off until ready to start the engine.

The most common problem with inverted engines is to have the low end too rich which will put the fire out in the glow plug. Just make sure the carb is adjusted properly and you will be fine.

EXCAP232

There are several options for getting around this problem. First off, if the engine is brand new, it's best to pull it out and bench run a few tanks of fuel through it, (engine upright), to break it in so you can get the needles set correctly. Then invert the engine on the bench and set up the fuel tank level to match the plane. Run the engine and re-adjust the needle settings. Clamp the fuel supply to the engine while filling the tank and don't remove the clamp until you are ready to start the engine. You might find that after all of this the engine will run fine inverted with the high fuel tank. As mentioned above, be sure to clamp the fuel line to the carb after landing to stop the siphon. Do NOT prime the engine in this set-up and an electric starter is usually needed to get the engine running quickly as soon as the clamp is removed from the fuel line. A Cline regulator is another option for this problem if all else fails.

I mounted a brand-new .46 FX onto my laser 3d (inverted) did the breakin inverted and all that. The only time that engine's been upright is doing inverted maneuvers. Set all the needles right and you won't have a problem. And when you're not flying, either set it wehre the nose is significantly higher then the tail or clamp your fuel line (I use hemostats).

Assuming your engine runs OK with the tank that much higher then there's one simple way to stop the syphoning without using clamps etc. Run your vent line to the bottom of the tank instead of to the top. So long as the vent line is the ONLY way to get air in the tank (any fill line if used must be blanked off) then syphoning becomes impossible. The only drawback is the model must be inverted to fill the tank.

Thanks everbody for your inputs. Although it doesn't look as nice, I think I am going to turn it right side up. On the next plane I build with an inverted engine I am going to mount the fuel tank in a different position so it is lower than the engine. Again, thanks for your replies.

It is not a good idea to mount the fuel tank lower than the carb. The opposite problem will occur, you might go lean at less than half a tank. Ideally, the center line of the tank should be on the same line as the center of the carb. In situations such as yours I usually use a fuel pump such as the Perry regulator the Kline regulator.

A lot more user friendly with the engine upright too, What with the glow starter on top, etc.

It is? What's the difference between reaching over a plane to grab the glow drive or reaching under it?

Aaron,
When putting the igniter on it's harder to find the glow plug when it's mounted inverted, especially on cowled engines. There's often limited space between the glow plug and the ground, and when taking it off, you're reaching in between the spinning prop and the wing.

Why are youi giving him a hard time?

Now, the best bet for inverted engines is to buy a cheap foam cooler and make cut outs so you can sit the plane in it upright for starting. Of course, then you have to turn over the plane with the engine running.
Dennis-

I'm not purposely trying to give anyone a hard time. It's just that I have one plane with an inverted engine, one with a sideways-mounted engine deep inside a cowl and have never had a problem.

Me neither: I had several and never had a flooding problem.
Werid isnt it. LOL

My Sukhoi is so anti-flood that after I prime it, by the time I get the glow driver on and start flipping the prop, the fuel all drained back into the tank??? I dunno what's up with that. I'm going to have to go in and elevate the tank a bit, I think.

Actually I spoke too quickly when I indicated I would mount the tank lower than the engine. I should have said re-position it in line with the inverted carb. As far as using the glow igniter I have a remote mounted unit in the fuse side that works very well and is safe.

I think maybe you guys have possibly gotten a little off track here. The fact that the engine is inverted isn't causing Ross8236's problem , it's the height of the fuel tank vs. the carb.

You said it Stick. I knew what the problem was. Just was looking for suggestions on how best to fix it.

No: Iam not off track here. I understand what his problem is. LOL
I was just stating I HAVE never had that problem. [:@]
The first thing that came to my mind was bad kit/arf
design. Again all i build is Sig kits and maybe thats why i have never
had that problem. LOL

No offense, but telling Ross8236 that you have never had that problem doesn't really help him does it? Nor does LOL.

I wasnt laughing out loud at him. I WAS LOL AT YOU COMMENT TOWARDS ME. LOL
LOL,LOL,LOL.

Mr, dont never come on here a tell a me that iam off track when
you havent a clue. LOL

Only valid point you made was my comment didnt help him.
which in the first place wasnt intended to it was just a statememnt.

I believe this was your first post to this thread.

I believe I was quite polite in saying "I think maybe you guys have possibly gotten a little off track here." If you look at post #3, I did offer some possible solutions to the original post.

You don't mention if the tank outlet height is parallel with the tank centre line. But assuming it is, there's the root cause of your problem. Fix it.

The engine being inverted isn't the cause of your problem. An inverted engine will run just as well as an upright one. Starting wise they are more prone to flooding through mishandling, or as in your case an inbuilt flaw. As you've already correctly identified, the cause of your problem is the "considerable" differential between outlet (& presumably median tank) height (?) and your carb height.

Even if you patch the immediate flooding problem, the engine will never run well for the full tank as feed is suction induction assisted by muffler pressure. You'd be pushing uphill even wih crankcase pressure.

The proper solution is to re-engineer by either lowering the tank to lower the median fuel level or raising the engine mounts to raise the carb height. Rotating and mounting the engine upright will also work if it brings the carb inlet approximately level (+/- ½in) with the centre line of the tank.

Using pinch devices to temporarily stop static flooding ain't gonna' work. It's going to start flooding rapidly as soon as you take it off. Even if you're quick, if you're using an electric starter for starting, hydraulic locking and engine damage with this problem is inevitible. If it was me I'd just bite the bullet, get stuck in, and fix the root cause.

Nice post:Every thing you said sounds logical to me.
Gee: If had to pinch the fuel line every time i fueled
up i would go crazy. LOL

Its not likley that i will ever have this problem but
i printed you post just in case.

Not true. I own a warbird powered by an inverted Saito 1.00. The bottom of the fuel tank is level with the carb and can't be changed due to the design of the aircraft. I installed a miniature ball valve in the carb supply line which is closed during fueling and opened when ready to start. The engine always fires immediately because it was properly broken in and tuned on a bench stand first. Once the engine is running it performs normally on the ground andin the air with no tendency to flood. I agree that in this situation you do have to be careful of the possibility of hydraulic locking should the engine fail to start on the first try, but engine damage is not inevitable if you are aware of what is taking place. Hydraulic locking can occur in almost any setup. The best way to avoid engine damage is to use a starter that is not overly powerful for the application and don't use a car battery to power it. Even in a normal setup with the center of the fuel tank level with the carb, siphoning can occur when the tank is full due to the fact that fluids seek their own level.

Sig,
Thanks for the info. I am waiting for a new cowl to install the engine in its designed position (inverted). I will probably try and relocate the vertical position of the engine so that the carb will be in line +/- 1/2" of the fuel tank outlet as you suggest. I will, however, try it before I make any cutouts in the cowl. As it is presently set up with the remote fueler mouted at the bottom side of the fuse, fuel comes from the tank to the bottom of the fuse and then back up to the carb which is probably 1 to 1-1/2" below the level of the fuel tank outlet. I am currently running the engine in an upright position with no problems, but esthetically it doesn't look very nice with the cylinder projecting from the top of the cowl. Again thanks for your input.

You probably won't be able to make much of a vertical adjustment on the engine as the spinner needs to be centered on the cowl. You'll need to lower the tank if possible. Don't gauge the tank placement by the fuel outlet height, it's the level of the tank itself that matters. Center of the tank should be level with the carb for best operation. Whether the tank has the outlet in the center or closer to the top doesn't matter, the fuel inside is going to seek it's own level either way.