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Mounting a O.S. Fs 120se w/o pump

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Mounting a O.S. Fs 120se w/o pump

Old 01-09-2014, 07:29 AM
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RANGER61
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Default Mounting a O.S. Fs 120se w/o pump

Hello Masterminds of the RC world.....
Unlike most of you I am not yet or anywhere near a mastermind of most of you on this site. My hat is off to the vast majority of you in your experience and skills.
this will be my third year in RC Airplanes.
here is my question.......I just got delivered to my door my new Escapade 61 (68inws) I decided to go big on the engine and bought a O.S. fS 120 se (four stroke) will I be able to use the cowling with this engine? They show it built with a 2 stroke 95.....but not with the four stroke. Will I have to forget my wishes of a cowling and run my four stroke with the "cheeks"?
the four stroke is just going extend throughout the end of the cowling too much I think. I really wanted to install the cowl. anyone of you masterminds can think of a solution that would be very helpful thanks

RANGER 61
Old 01-09-2014, 09:42 AM
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opjose
 
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IMHO: Even a standard 60-75 two stroke engine installation requires an extensive hack job on the cowl to make it fit that cowl.

The plane is set up to use an upright mount engine, that in a pinch could be mounted upside down.

With your larger engine you are looking at cutting even more of the cowl away and you'll have problems getting the cowl on and off without large cutouts.

Consider not using the cowl at all.

In your shoes I'd be attempting an inverted engine mount instead which would leave the muffler hanging down and back preventing oil from getting onto the plane.

This would also make it easier to get the cowl on and off with one opening on the bottom, and will be less unsightly.

This kind of thing is not really for the novice though.

Some will tell you that running engines inverted is problematic.

Don't listen to that nonsense, they merely don't know how to tune their engines properly.

You may have to spend a bit more time making sure that you have the engine tuned up and you should run the engine uncowled until you have the plane flying reliably for your own ease.
Old 01-10-2014, 10:55 AM
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RANGER61
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Thanks,
I hadn't even thought of mounting the engine upside down. With your comments on the advantages of doing so, it,s compelling. I am looking at the aspects of mounting upside down.
I know it would be much easier to just forget the cowl and mount the engine with the cheeks, but it just wouldn't look as cool.
Old 01-10-2014, 01:38 PM
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opjose
 
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The only caveat mounting the engine upside down, is idle tuning.

Use the "ignitor" trick to make sure the LS needle is set properly, then adjust the HS needle and go back and double check the LS again using the same trick.

The "ignitor trick" is as follows:

- Start the engine and let it warm up, you can even do this with the plane inverted ( engine upright ).
- Adjust the low and high speed needles as much as possible
- With the plane upright, remove the ignitor and observe the behaviour of the engine at idle.

If:

- The engine slows down or stops the engine is too rich, Lean it out 1/4 turn and try again.

- If the engine does not slow down richen the engine 1/4 turn and try again.

--

- Remove and install the ignitor until you find that point where the engine just begins to slow down, lean until this stops
- Now richen the engine 1/8 of a turn and check the HS needle again.

This will prevent the engine from bogging down in flight or on the ground.
Don't forget a nose up test too.

When starting the plane, assume it needs very little priming if none at all.

With most of my inverted mount engines I use an electric starter and I do NOT prime the engine at all.

I let the starter turn the engine over until it starts.

Other than that, having the engine inverted is no different than an upright installation.

You DO want to close down the throttle and keep it that way once you stop the engine to prevent fuel from leaking into the head.

Also before you install the ignitor and hit the engine with the starter the second or subsequent times of the day, make sure you can turn the engine over fully.

The idea is to prevent hydro-lock.

---

On that plane, you'll put the cowl on. The head will hang down, and then you install the muffler assembly.

Likewise to remove the cowl you'll remove the muffler and pipe first.

Last edited by opjose; 01-10-2014 at 01:41 PM.
Old 01-11-2014, 02:13 AM
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sj3cub
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The only concern I have when mounting my four strokes inverted, is can I get the centerline of the fuel tank low enough in the fuse to line up in the correct relation to the needle valve/carb. Sometimes its possible, sometimes its not. This is where a lot of people run into problems when mounting inverted, and don't even realize it. If you had the pumped version, there would be no issue. Good flying!
Old 01-13-2014, 10:00 AM
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opjose
 
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Originally Posted by sj3cub
The only concern I have when mounting my four strokes inverted, is can I get the centerline of the fuel tank low enough in the fuse to line up in the correct relation to the needle valve/carb. Sometimes its possible, sometimes its not. This is where a lot of people run into problems when mounting inverted, and don't even realize it. If you had the pumped version, there would be no issue. Good flying!
The "problems" they run into is believing some of the hype about fuel tank height espoused around here.

MOST of it centers around "junk science" that has no basis in fact.


There is only a small issue of concern, which is not "junk science" and that is siphoning.

If the height of the fuel line ( top ) when the tank is FULL is higher than the spray bar, you can get siphoning.
Siphoning is of course bad, because you can flood the glow plug or even hydrolock the engine.

However once the engine is properly tuned, the spray bar oriface is quite small, and given the average 1 to 1.5" DIFFERENCE in height seen when inverting an engine, that leads to maybe a single DROP of fuel siphoning out evey minute or so with the engine throttle at idle.

If you shut down the throttle fully ( engine cut off ) you should see no siphoning, unless of course you have other plumbing problems.

So you set up your filling system so that fuel can not be pushed into the cab during fueling. You keep the throttle cut setting on once the tank is full, and you DO NOT prime the engine before you attempt to start it.

That is all you need to do...

Also remember that with most tail draggers, when the plane is on the ground the engine is lifted even higher than the thrust line. That often offsets the tank height difference enough to also stop siphoning.... either way it is not a big deal once you have everything dialed in and the pilot exercises a bit of care.


The rest of the nonsense about small tank height differences affecting engine performance is all speculative hype.

Some people will go as far as to talk about the difference of the thickness of a PLAYING CARD making a difference.... they are crazy.

Our planes would be cutting out when they fly inverted, change attitude or even when climbing were they to be correct.

Once running your four stroker engine sees no change if you raise the tank 3" or drop it 3". It takes a LOT more distance to cause the weight of the fuel in the line to affect things.

Last edited by opjose; 01-14-2014 at 01:18 PM.

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