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engine thrust line

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Old 07-25-2014, 09:47 AM
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Stick 40
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Default engine thrust line

I want to put a different engine in a plane and don't really know the thrust line, is to be on the same line as the horz stab???

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Old 07-25-2014, 08:48 PM
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jester_s1
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That depends on the plane. If it had an engine in it before, the thrust line will be in the middle of the mounting holes in the firewall.
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Old 07-27-2014, 03:49 AM
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Stick 40
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I did some more looking into this and I guess I did not ask the question right.

Its a Slow Poke and I am changing from a .40 2 cycle to a Saito .50 and was wondering if the prop shaft has to be on the same plane as the old engine prop shaft. Same level up and down to say it simpler, just trying to make this clear as I can. I don't think its a big deal on that plane, as long as its close.

I think from what I read that the thrust line should be in line with the main wing center line, may be a little down thrust if needed.

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Old 07-27-2014, 05:46 AM
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It won't matter. There are no actual rules on where the engine thrust line has to be relative to the datum line or the wings or tail. The plane's designer figured out what worked best on that particular airframe, but even then a move of 1/4 inch up or down isn't going to make any difference. Are you thinking of moving it up or down for clearance reasons? The really important thing is the thrust angle, which may change since you'll be swinging a prop that's so much bigger.
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Old 07-27-2014, 06:08 PM
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Stick 40
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no, I was not planning on moving it. Just wondered what it would cause if I did not get it right where it was before.

I have only built kits and ARF's in the past and put everything where I was shown.

I put the engine in already and its very close to the original.

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Old 07-29-2014, 11:32 AM
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Hi!
There is a wide variety where you can put the thrustline on a model. Just feel free to experiment!
For instance on my Marutaka (Balsa kit from the late seventies) the thrustline is 0-0 ,that means the engines point straight forward with no up or down thrust.
If we compare it to the Top Flite DC-3 in about the same (a balsa kit from the nineties) in the same size as my DC-3, they call for a several degrees of down trust and several degrees of out-board trust.
Why this discrepancy you might ask!? Well! It probably due to a that Top-Flite wanted their model to be very safe to fly on just engine (in case of an engine failure) and not bothering with too much scale factor.

Most low winged and mid-winged models have 0-0 degrees thrust line. A general rule is that the lower the engine is mounted (or higher the wing) the more down-thrust is required.
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Last edited by jaka; 07-29-2014 at 11:35 AM.
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Old 08-04-2014, 08:29 PM
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It will not change when you mount a different engine. All engine prop shafts are level with the bottom of the mounting flanges.

Kurt
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Old 08-05-2014, 04:18 AM
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That sound good, that makes sense . But I got crazy and put this one in the ground and broke the wood mound. I am putting in a nylon mount and a different engine, I can still see close to where the old line was.
Just wondered if it would be critical as to the exact line, guess it isn't.

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