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Old 04-19-2012, 04:23 PM   #1
npowell28
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Default Finding a COG on scratch built plane

Is there a way to find the COG on a scratch built plane. I've seen the excel tools that calculate either MAC or COG but as far as i can tell you need one or the other to finish the calculation.

I am using airfoils that i have plotted myself e.g. Clark Y. Am i right in saying that its the airfoil that has the cog and not the plane e.g. each airfoil has an establish COG and you balance the plane on that. Have i got this right. I've just finished building a home built UAV type thing based onthe clark Y airfoil. I've been putting off flying it until i can establish what the correct COG should be.

Thanks guys and gals.
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Old 04-19-2012, 04:51 PM   #2
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Originally Posted by npowell28 View Post
Is there a way to find the COG on a scratch built plane. I've seen the excel tools that calculate either MAC or COG but as far as i can tell you need one or the other to finish the calculation.

I am using airfoils that i have plotted myself e.g. Clark Y. Am i right in saying that its the airfoil that has the cog and not the plane e.g. each airfoil has an establish COG and you balance the plane on that. Have i got this right. I've just finished building a home built UAV type thing based onthe clark Y airfoil. I've been putting off flying it until i can establish what the correct COG should be.

Thanks guys and gals.
Optimal COG depends on several factors as well as subjective handling preferences. This calculator: http://adamone.rchomepage.com/cg_calc.htm takes the tail area and distance from the wing into account. It's been pretty reliable for me.

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Old 04-19-2012, 05:23 PM   #3
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What post number 2 said about finding where the CG should be. To answer the original question, just find where the plane balances and the CG will be somewhere on the vertical line above or below the point where it balances. Every thing has a CG, it may not even be within the structure you are measuring. I think your question should have been "How do you find where the CG SHOULD BE for a successful flight, not "how do you find where the CG is".
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Old 04-19-2012, 05:46 PM   #4
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Originally Posted by Rodneh View Post
What post number 2 said about finding where the CG should be. To answer the original question, just find where the plane balances and the CG will be somewhere on the vertical line above or below the point where it balances. Every thing has a CG, it may not even be within the structure you are measuring. I think your question should have been "How do you find where the CG SHOULD BE for a successful flight, not "how do you find where the CG is".
Lol! yeah your right about the succesful flight bit. I'll try that program. If others are using it successfully then that gives me confidence.

Thanks
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Old 04-19-2012, 06:13 PM   #5
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Originally Posted by pmullen503 View Post
Optimal COG depends on several factors as well as subjective handling preferences. This calculator: http://adamone.rchomepage.com/cg_calc.htm takes the tail area and distance from the wing into account. It's been pretty reliable for me.
+1

Use a static margin of 10% as a starting point.
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