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Old 01-20-2013, 10:45 PM   #1
CNY_Dave
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Default Why on earth do my plans say to set CG with the wing off?

5lbs clipped-wing cub, plans say to set the cg with the wing removed... I have to say that's a new one on me.

I'm going to set as advised, then see if that looks 'ok' when I check it on the wing.

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Old 01-20-2013, 10:48 PM   #2
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That makes no sense at all. The wing will likely move the balance point back a bit when you install it so balancing without the wing in place is pointless.

It will also be harder to do as you wont have the underside of the wing to support the model from.
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Old 01-20-2013, 10:52 PM   #3
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Yeah that does not make sense at all unless the balance point is exactly half the wing cord.

Still, I think I would want to balance it via the traditional method.

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Old 01-20-2013, 11:14 PM   #4
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Yeah, I generally ballance my planes to the main spar, or about 1/3rd back from the leading edge.
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Old 01-20-2013, 11:17 PM   #5
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Originally Posted by hayofstacks View Post
Yeah, I generally ballance my planes to the main spar, or about 1/3rd back from the leading edge.
That's about the norm for sure. How would you even balance it without the wing on it?

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Old 01-20-2013, 11:40 PM   #6
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This is a 1970s vintage midwest kit that I'm converting from gas, on the plans a big arrow points to the bottom of the fuse about 1/3 back from the front of the wing, manual says to balance with the wing off.

Balancing it is easy, just put a block of wood with a dowel on top under the fuse, if it's balanced it'll take a while to tip either way.

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Old 01-20-2013, 11:48 PM   #7
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Interesting, I'd be curious to see where it balances once the wing is on based on doing it that way. I'd say it will be right where one is normally balanced, about a 1/3rd way back or so on the wing

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Old 01-21-2013, 07:21 AM   #8
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They probably are giving a balance point that you would have, if you balanced the plane the "normal" way then removed the wing and checked where the fuselage would balance without the wing.

Doing it this way on some models, makes it easier to insert the battery or weight to balance, without taking the wing on and off every time you try a different position.

I have a carrying handle that bolts in place of the wing on my 63" Sig LT-25, it is marked where the body with the battery should balance. I use several different packs in this plane, so it is easier than having the wing in place.

And in case you think his instructions are strange, look at the way the manual told how to balance the Hobie Hawk.

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Old 01-21-2013, 01:53 PM   #9
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Since this model has not been covered with monocote, but is all balsa and fiberglass, I wonder if the wing's contribution is different?

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Old 01-21-2013, 02:29 PM   #10
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Originally Posted by CNY_Dave View Post
Since this model has not been covered with monocote, but is all balsa and fiberglass, I wonder if the wing's contribution is different?
good point, anything that changes the original specifications weight wise could throw off the CG setting it with the wing off.

Both my cubs, a 40 size Hangar 9, and a 1/4 scale PA-12 balance right on the main spar. I'd say you would be safe setting it about that point. It will be flyable enough and you can tweak it from there.

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