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.

How long is the nose on a Strega?

Just a thought, Why not ask Windy ?

Weight(original) x Distance(original)=Weight(new)xDistance(new)

Works for me.


Jim

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. 

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.

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.