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Old Sep 22, 2007, 03:18 AM
Thermalin is offline
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I'm a pilot, 100 yrs too late
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Question

Balance CG of low wing plane


I see in ads for cg balancers the low wing aircraft are shown inverted. Is this so it will hang in a more stable manner having the majority of the weight below? I would think wether it's balanced right side up or upside down, the cg location would be the same.

I'm getting ready to begin balancing my four star .40 and after 4 months of work... I don't want to re-kit it on takeoff.
Mike
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Old Sep 22, 2007, 04:30 AM
linw is offline
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Yep, just because it is stable while upside down. Makes no diff to CG.

Good luck with the maiden, Mike. We certainly don't want to see it back in kit form
Old Sep 22, 2007, 11:50 AM
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Quote:
Originally Posted by Thermalin
I would think wether it's balanced right side up or upside down, the cg location would be the same.
The CG will be in the same place of course but we're not concerned where the vertical location is (somewhere near the centre of the fuselage) but only its position lengthwise. Putting a model on a balancer so that its vertical location is below the support just lets it act like a pendulum and hang in a stable position.
Old Sep 25, 2007, 05:31 AM
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almost impossible to balance a low wing right side up..I'll bet it would fall off the balancer before you got it. inverted is the way to go
Old Sep 25, 2007, 10:53 AM
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Here's how I did my 4*60. mark the CG from the LE of wing on the center bottom of the Fuss. then put a small Eye screw in that spot. Take it out and put a drop of CA (thin) in the hole (to harden the treads). When dry replace the Eye screw and tie mono fishing line or heavy string (enough to support the wt.) then hang it from something in a open area. It should hand prefectly flat, front to back and side to side. Change placemant of things inside or add wt. at high points.
Old Sep 25, 2007, 10:41 PM
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Quote:
Originally Posted by RICMOD5634
Here's how I did my 4*60. mark the CG from the LE of wing on the center bottom of the Fuss. then put a small Eye screw in that spot. Take it out and put a drop of CA (thin) in the hole (to harden the treads). When dry replace the Eye screw and tie mono fishing line or heavy string (enough to support the wt.) then hang it from something in a open area. It should hand prefectly flat, front to back and side to side. Change placemant of things inside or add wt. at high points.
Why wouldn't you want it slightly nose down as in conventional high wing right side up balancing? (I like the eye screw idea.. lets you balance fore/aft and left/right all at same time)
Mike
Old Sep 26, 2007, 12:46 AM
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Quote:
Originally Posted by Thermalin
Why wouldn't you want it slightly nose down as in conventional high wing right side up balancing? (I like the eye screw idea.. lets you balance fore/aft and left/right all at same time)
Mike
Only valid if you want the CG at one certain point, and you better know where that point is.

I use the *sling method* to check the CG. Always right side up.

I assume that a few pilots know what that is. Hang the plane in slings on the wings and a plumb line pointing to the CG.
Old Sep 26, 2007, 02:04 PM
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Originally Posted by indoruwet
Only valid if you want the CG at one certain point, and you better know where that point is.

I use the *sling method* to check the CG. Always right side up.

I assume that a few pilots know what that is. Hang the plane in slings on the wings and a plumb line pointing to the CG.
I usually start in the middle of the range on the plans and adjust after a few flights if necessary...

What is the sling method... from what I'm envisioning.. a sling on each wing... (think stork carrying a baby in a sling) will keep the plane nose from pitching up or down??

Mike
Old Sep 26, 2007, 05:12 PM
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Originally Posted by Thermalin
What is the sling method... from what I'm envisioning.. a sling on each wing... (think stork carrying a baby in a sling) will keep the plane nose from pitching up or down??
This makes sense ? Only works if CG is somewhere in the sling area ... which it always is ...

The sling should be wrapped around the rod on top a few times to create a bit of friction.
Old Sep 26, 2007, 07:03 PM
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Originally Posted by indoruwet
This makes sense ? Only works if CG is somewhere in the sling area ... which it always is ...

The sling should be wrapped around the rod on top a few times to create a bit of friction.
I;ll have to give it a try.. I think I can see how the fuse will swing for and aft now... but seems like it would be insensitive to minor changes. Would it beneficial to have a the dowl at the top be as small in diameter as possible to increase the accurace. Think of it being a large diameter and you'll see what I mean.. would limit the sensitivity which you don't want.
Mike
Old Sep 27, 2007, 01:53 AM
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Originally Posted by Thermalin
Would it beneficial to have a the dowl at the top be as small in diameter as possible to increase the accurace. Think of it being a large diameter and you'll see what I mean.. would limit the sensitivity which you don't want.
Mike
The sketch is not *to scale*
The top dowel is actually a 1/4 inch diameter steel rod.
Old Oct 04, 2007, 09:56 PM
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Upside down...


I like to use the Great Planes CG Balancer...
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