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Old May 26, 2016, 06:39 PM
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Inverted Engine

While looking at a bunch of old plans, I noticed many have inverted glow engines. I have never had one and been told of issue's, but wondered about experiences from those who have actually tried them. Thoughts anyone?
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Old May 26, 2016, 06:45 PM
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I've done a few of them and the only ones that I felt were worth the hassle were pump equipped engines. Non pumped installations were either more work then I wanted once at the field or were less the 100% reliable.
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Old May 26, 2016, 06:54 PM
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Apparently something about the fuel putting out the glow plug under certain conditions?
At least from what I've read. I've only had a couple glow planes. Fuel is way too expensive.
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Old May 26, 2016, 06:56 PM
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I have a super chipmunk with a Saito 82 inverted and it runs just like it did
When installed upright.
It's important when installing inverted to have the centerline of the fuel tank just a touch below the centerline of the spraybar on the carb.if this can't be done then a
Pump might be needed.
I've never mounted a 2 stroke inverted can't help you there
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Old May 26, 2016, 07:11 PM
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Quote:
Originally Posted by Tucci View Post
Apparently something about the fuel putting out the glow plug under certain conditions?
At least from what I've read. I've only had a couple glow planes. Fuel is way too expensive.
Yes, the tune had to be right on the money but my issues were more related to fueling/starting. Cbfn1 is correct the center of the tank should be below the carb spray bar otherwise the fuel will siphon and flood the engine. I always put a fuel clamp on the carb line so the fuel could not get to the carb while fueling. Open the clamp and start immediately. Worked well unless you had a dead stick or did not shut the clamp right after shutting down. Then the fuel would flow and could fill the cylinder. If unaware of the cylinder being full of fuel, you could easily damage the engine by hitting it with a starter. It can be done reliably but is more work then an upright install. A pumped engine such as the YS engines does not suffer these issues.
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Old May 26, 2016, 07:28 PM
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Quote:
Originally Posted by Cbfn1 View Post
I have a super chipmunk with a Saito 82 inverted and it runs just like it did
When installed upright.
It's important when installing inverted to have the centerline of the fuel tank just a touch below the centerline of the spraybar on the carb.if this can't be done then a
Pump might be needed.
I've never mounted a 2 stroke inverted can't help you there
Yes, tank position must be right or you can have flooding problems. Like he said tank center line should be it bit lower than spray bar. I have flown many airplanes with inverted engine with no problem. Clarence Lee 's R/C engine book has several answers to this same problem. Once running inverted has no effect. If it did you couldn't fly inverted. Some guys start their inverted engine planes upside down to solve the flooding when starting problem.
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Old May 26, 2016, 07:37 PM
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I run most of my engines inverted and the only problems I have are during fueling, getting the fuel line back on the carburetor nipple, and finding the glow plug without standing on my head.
I run 4 stroke engines exclusively, Saito and YS and I usually leave the glow plug battery on until the engine is warm. My engines idle and run fine after that and don't seem to know they're upside down.

I try to center the tanks so the outlet is about the same height at the carb inlet.

Tom
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Old May 26, 2016, 09:07 PM
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If you can tune the high and low speed properly upright, you won't have a problem inverted either. +1 on tank position also!
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Old May 27, 2016, 02:46 AM
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So true, Mike.
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Old May 27, 2016, 07:55 AM
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I have run 2 stroke engines in EVERY possible orientation, including vertical shaft, both pointing up and pointing down, and 4-stroke upright, sideways, inverted and vertical shaft down.

Installed properly, a glow engine runs the same, regardless of upright or inverted, sideways left or right, with the possibility of less reliable idle when inverted due to the possibility of oil pooling in the head. But I have never encountered that myself.
But indeed some issues during starting can occur.

The flooding issue that exf mentions (flooding with stopped engine and full fuel tank) is very real on fourstrokes but impossible on normal 2-strokes with a front carb, since the carb is now pointing downwards and the fuel simply flows out of the air intake. It does not first flow upwards all by itself into the induction port.....
Hydrolocks at the first start of the day, due to oil collecting in the combustion chamber during storage is a very nasty and real problem with 2 strokes but should not occur on most 4 strokes due to the valves being in the head.
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Old May 27, 2016, 08:14 AM
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What is it that makes one position the upright position?
It can't be the direction that the cylinder points, because
there are flat twins and fours, and radials that have them
pointing at different directions. It can't be the carb, either.
They point different directions for helicopter engines and
flat four engines.

If there was an oil sump, maybe that would tell, but since
aircraft fly in different positions that wouldn't tell much.

The only thing that I can see is the writing on the side,
and that has no effect on anything.

Jenny
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Old May 27, 2016, 10:06 PM
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For single cylinder engines the cylinder is pointing up for the upright position.
For a single cylinder engine, the cylinder points down for the inverted position.
For a single cylinder engine, the cylinder points sideways for a horizontal position.
Now you could have the cylinder pointing at a angle, say 45 degrees. Some airplane designs have to position the cylinder at a angle so that the muffler is inside the cowl underneath.

Actually if the engine has the glow plug directly in the top center of the combustion chamber, then angling the engine so that it isn't exactly inverted but at a angle works well. Then the glow plug isn't at the absolute bottom most part of the engine where oil and fuel can accumulate drowning out the glow plug.
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Old May 27, 2016, 10:16 PM
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An upright RC model engine installation:


An inverted model airplane engine:




Side mounted engine:




Here is an example with the engine mounted at a angle other than striaght up or down, thus the muffler will be directly down under the cowl.

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Old May 27, 2016, 11:48 PM
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So......how would you define this install?
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Old May 28, 2016, 04:12 AM
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A horizontal twin, mounted upright....

You can mount it upside down (most likely the exhaust stacks will be pointing upwards then).
It will look silly most likely, should run more or less the same, but might encounter starting problems due to exhaust residue running back from the muffler into the combustion chamber at standstill.

(without precautions for this, glow engines are horrible to start, when mounted with the exhaust port facing up, ask any RC-biker that runs fuel. Probably gas engines are less affected)
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