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Building Tips and technical articles. => Building techniques => Topic started by: Gordon Tarbell on December 11, 2006, 07:56:09 PM
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when figuring how much to shorten nose for heavier engine. Would it be correct in comparing the two different set ups(long nose/light engine and shorter nose/heavier engine ) by converting both to ounce inches from design cg or do the stunt gurus just use SWAG (some wild --- guess). Plane in question, Strega, probably designed for a ST60 , thinking about a big block Saito 72.
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Now this is just "me" I with that heavy of an engine I would shorten it as much as mechanically possible. But Randy Smith would have a better idea. Drop him a PM and ask.
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How long is the nose on a Strega?
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Prop hub to LE 10 3/4" or 13 1/2 from indicated CG engine shown on plans is a 61lite RE Double star. Others are listed including Saito 56 and 72 . Just unsure wich way to fall off the pot.
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Just a thought, Why not ask Windy ?
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I think that most that have used 4-strokes would opine that shortening the nose isn't necessary....for some reason (explained a couple of times, but still not understood here) they are drop-ins.
Windy's only purpose built was the Spit with the Saito .90...
I know that Zambelli has tried 4-strokes in many aeroplanes that previously housed 2 cycles and he hasn't modified the nose.
See Ya
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Weight(original) x Distance(original)=Weight(new)xDistance(new)
Works for me.
Jim
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you should measure from the cg of the engine to the cg of the plane. The engine cg on a single cylinder setup is more or less right in the corner where the shaft meets the cylinder.
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Interesting point Phil. But what difference to the models C.G. does the engine's C.G. make when the engine is fixed to the airplane anyway? Now my head hurts. n~
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When doing the weight x distance calculations, the distance used is the distance between engine CG and the model CG.
Jim
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the differences come in where you might be retrofitting a 4 stroke with a fairly long shaft , or sticking a short shaftengine into a spot where you had a motor with a shaft extension. If ou just pick a fixed point, like the edge of the backplate, the calculation could be off enough that you might as well just cut and try. That is what I usually do anyway. Good planes don't seem to be terribly critical of an ounce or so of nose weight, most of the time.
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One additional consideration, especially when going from a 2-stroke (ST .60) to a Saito.72 is that the Saito will require a much smaller tank. Lighter tank, lower fuel load; maybe not quite as much shorter as engine-only calculations suggest. Just a thought . . .
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What would be a good size tank to run this Saito 72 on ? I was going to stuff the largest clunk tank I could squeeze into it. Also I was planning on running the YS20-20 fuel mix. If I allow for the higher nitro fuel and end up cutting back on % then I will still have enough capacity in tank.