Idiosyncrasies of Inverted Engines - RCCanada - Canada Radio Controlled Hobby Forum
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Old 07-23-2010, 08:19 AM   #1
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Idiosyncrasies of Inverted Engines

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I am running an OS 61 FX inverted in a Hangar 9 P-51. I have noticed that the engine is not nearly as reliable as I would like. On my first flight this year with this aircraft I had a dead stick only a few minutes into the flight. I changed the plug to a new one (OS # eight) and it seemed to help.

I was just wondering, is it normal for inverted engines to be a bit fussier and even die outright from time to time (ie excess fuel kills the glow or something?)?


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Old 07-23-2010, 08:41 AM   #2
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Re: Idiosyncrasies of Inverted Engines

Make sure that the engine can cool properly. Air directly to cylinder and head as well as a way for the hot cooling air to get out, also make sure the center of the tank is below the center of the carb. If your engine has remote needle, you can move the remote needle above the center of the tank.

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Old 07-23-2010, 09:23 AM   #3
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Re: Idiosyncrasies of Inverted Engines

As far as I'm concerned any 2 stroke or 4 stroke mounted inverted is a handicap.
It might work consistent for some, but I have never had much luck myself.

They simply load-up too easilly.

I put the big OS BGX-1 (35cc), in an 85" Edge inverted.
Wound up spending more time fussing with it than anything else, , , , what a mistake.
I switched it over to horizontal and a Pitts muffler, , , never had the slightest problem since.

Last edited by Mike Emilio; 07-23-2010 at 09:30 AM.
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Old 07-23-2010, 10:25 AM   #4
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Re: Idiosyncrasies of Inverted Engines

The largest engine I have run is a 1.20 4 stroke.

I have run many engines of different sizes. Be they 4 stroke, 2 stroke. upright, sideways, inverted, sport or racing engines. Once they were set they all ran OK, no difference. All of the usual rules apply, cooling, muffler pressure, tank/carb position, etc, etc.

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Old 07-23-2010, 10:37 AM   #5
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Re: Idiosyncrasies of Inverted Engines

Originally Posted by kip51035 View Post
If your engine has remote needle, you can move the remote needle above the center of the tank.

The position of the remote needle does nothing. It is the position of the spraybar & venturi (where the fuel comes out) that determines how the engine runs in relation to the fuel tank.

VERY different things...

I am with Ed... a properly set up engine, with a good plug and proper tank location should allow the engine to run just as well upright, inverted or sideways.

How come so many guys with good running upright engines, dont have issues with flying around inverted, for extended periods of time (you know, doing inverted circuits)? Its no different.

Inverted engines need a proper set up/tuning to run ideal.

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Old 07-23-2010, 12:24 PM   #6
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Re: Idiosyncrasies of Inverted Engines

While I wold agree with Ed and AJC that properly setup the engine should run fine, I have found that 4S are a little more forgiving than 2S probably because of the offset of the glow plug.
That having been said you may find that your 61FX may never setup properly because the needle seat is cast as part of the backplate and the heat transfer makes needle setting on this engine unreliable. I had one on a Stik (side mounted wide open no cowl) for one season and it was the most frustrating engine I have ever owned. Was always quitting one me.
Since then OS has introduced the AX series of engines with the needle either back on the carb angled backwards or with a composite needle which they claim in their own advertising reduces heat transfer to the needle seat and fuel bubbling/foaming.
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