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Old May 21, 2012, 10:54 AM
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What effect does monokote covering have on influencing the CG

I have done a rough balance of a Great Planes PT60 and it seems to balance correctly un-covered, I was wondering what effect monokote will influence the weight?

See Pic

Thanks,
Tom
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Old May 21, 2012, 11:52 AM
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I've done a pre-covering rough balance on most of my planes. It seems (if memory serves) that the CG will move a bit to the rear. I usually add trim to the fin/rudder and stab/elevator - both sides. And fuse side trim all the way to the fuse end. (I use Ultracote).
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Old May 21, 2012, 02:59 PM
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I see your engine has no prop or spinner on it, so that will give you some room to work with too. The APC's are heavy, MAS's less so, and woods are usually pretty light.

When I'm as close as you are, I start to fine tune the CG with things like wheel selection (ex. Sullivan Skylight vs heavier rubber vs very light foam)

Did you lay some pushrods in the fuselage? They weigh too. Nylon tail skids, horns/bolts and other bits of hardware do add up too.
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Old May 21, 2012, 04:26 PM
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Oh yea - APC props in the 11 / 12 inch range weight 1.7 to 1.9 oz. Whereas a wood prop like a Zinger or MAS weigh in at .7 to .9 oz. - a full oz. difference. Harry Higley sells hubs & mini-spinners with or without a locking nut. You can add up to 3.0 oz. with the heavy bits. There is a debate - how detrimental is weight that is added to the engine's crank.
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Old May 21, 2012, 11:18 PM
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Thats a great plane your gonna love it. I have a pt40 (not the mkII) that i built roughly 15 yrs ago. I finally joined a club and have some time to fly know at 36 yrs old. The plane flies great. I would suggest you go with the bolt on wing if it's not to late. I wish mine was bolt on.
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Old May 21, 2012, 11:30 PM
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Never too late to convert to bolt down wing. The exercise will just give you an excuse to update the covering.
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Old May 22, 2012, 09:35 AM
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Quote:
Originally Posted by JohnGilmore View Post
Never too late to convert to bolt down wing. The exercise will just give you an excuse to update the covering.

That's very true John, but me personally I like the old fashon rubber bands. It kind of gives it that nostalgic look to it.

Pete
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Old May 22, 2012, 10:46 AM
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Pete - I'm not sure that there's a cure for what you have.
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Old May 26, 2012, 10:17 AM
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Pete - I'm not sure that there's a cure for what you have.
There is no cure for opinion.


Pete
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Old May 26, 2012, 03:29 PM
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Most of the surface area of the model is behind the c of g, so covering it will add more weight to the rear than it does to the front. So, it will get tail-heavy when you cover it, if it was balancing without covering.
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Old May 27, 2012, 10:33 PM
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Thanks of an "on topic" post. I second what you said.
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Old Jun 03, 2012, 10:34 PM
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This is the completed model PT60 it balanced to the CG of 4 1/8" just fine.
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Old Jun 04, 2012, 09:43 AM
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looks great
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Old Jun 05, 2012, 04:53 PM
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Your kidding?
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Old Jun 05, 2012, 04:56 PM
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Your kidding?
me ?
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