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CG on an odd shaped wing

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Old 08-09-2005, 04:53 AM
  #1
skoemba
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Default CG on an odd shaped wing

Ok all you Einsteins out there, I have a problem.

I have a odd shaped wing and I would like to calculate the cg. I tried some of the cg calculators I found in the forums but I am not sure if I am correct. I can also not get the exact shape on the calculators. Please help me out here guys (and girls?).

The wing is for a scratch build project.

Here is what the wing looks like. Please note that the dimensions are in millimeters.
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Old 08-09-2005, 02:44 PM
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Default RE: CG on an odd shaped wing

Quote:
ORIGINAL: skoemba
Here is what the wing looks like. Please note that the dimensions are in millimeters.
If this is an exact duplicate of the planform, I can find the MAC for the wing.

If it is not an exact duplicate of the planform, then post a pic that shows exactly what it looks like and I'll find the MAC for you.

Dan
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Old 08-09-2005, 11:35 PM
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Tall Paul
 
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Default RE: CG on an odd shaped wing

Add the chord dimension at the trailing edge break to the leading edge, and the sweep to this point, then the sweep from there to the tip, and use:
http://perso.wanadoo.fr/scherrer/mat...glish/mce.html
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Old 08-10-2005, 02:29 AM
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skoemba
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Default RE: CG on an odd shaped wing

Dan,

That picture was drawn on CAD and is the exact shape of the wing. Thanks for the help!

Tall Paul, can you please explain "sweep". Sorry, I'm still new to the terms!

Thanks guys!
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Old 08-10-2005, 09:09 AM
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Default RE: CG on an odd shaped wing

Quote:
ORIGINAL: skoemba

Dan,

That picture was drawn on CAD and is the exact shape of the wing. Thanks for the help!

Tall Paul, can you please explain "sweep". Sorry, I'm still new to the terms!

Thanks guys!
.Sweep is the distance the wingtip is aft of the root leading edge.
The 740 dimension in your drawing.
The program would need two sweep dimensions, as mentioned.. from the root to the leading edge at first break at the notch in the trailing edge, and the dimension from there to the tip.
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Old 08-10-2005, 10:05 AM
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erbroens
 
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Default RE: CG on an odd shaped wing

If you want to calculate the CG on your project, just a wing planform drawing is not enough. we should also consider is this is a flying wing, or if it has a horizontal tail, it´s area and distance from the wing. also the fuselage lenght and shape and even the airfoil affects the CG calculations.
Another way to do this by yourself, is building a small flat balsa model of your project and find the CG until you achieve a decent and stable glide rate.

Best regards, Enrique
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Old 08-10-2005, 08:46 PM
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Default RE: CG on an odd shaped wing

Hi Skoemba,

Quote:
ORIGINAL: skoemba
That picture was drawn on CAD and is the exact shape of the wing. Thanks for the help!
Okay. Here's what I found.

The vertical line is the MAC. The horizontal line is 25% of the MAC.

Dan
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Old 08-10-2005, 11:45 PM
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Default RE: CG on an odd shaped wing

I have about 4-5 DELTA wings. 25% of the MAC (virtical center line) is correct, but depending on the weight you have (I assume it is a pusher prop), the CG will come back a tiny bit farther

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Old 08-11-2005, 03:01 AM
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skoemba
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Default RE: CG on an odd shaped wing

Thanks a lot guys! I will try the CG Dan and let you know. I guess it's trial and error from hereon!
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Old 08-11-2005, 03:42 AM
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Default RE: CG on an odd shaped wing

Quote:
ORIGINAL: skoemba
Thanks a lot guys! I will try the CG Dan and let you know. I guess it's trial and error from hereon!
You're welcome. Yes, this is only a rough CG that will allow you to fly the model so you can fine-tune the CG.

Good luck and happy landings!

Dan
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