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Old Apr 18, 2002, 11:21 PM
Registered User
London Ont. Canada
Joined Sep 2001
64 Posts
I need to find the CG for a swept wing

I have made a new flying wing and I need to find the CG.

The wing is as follows

Tip: 4.75
Root:11.25

Wing span:40"
total height18"
height to trailing edge 6.75

I hope this makes sense

Where is Sparky Paul when you need him?

Any help you have would be great.
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Old Apr 19, 2002, 07:33 AM
Registered User
kingston Ont, Canada.
Joined Nov 2000
33 Posts
Might be a little hard to explain, but here goes. Take the root chord , add it to the tip leading edge. Take the tip chord, add it to the root trailing edge. Cross all 4 corners with a line. Where they cross in the middle is the mean aerodynamic chord or MAC. This is where you measure the CG from. On a flying wing the CG is between 15 and 20% from the leading edge.
Hop
this helps. If it needs more explaination let me know.
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Old Apr 19, 2002, 10:08 AM
Ascended Master
Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
13,371 Posts
http://home.earthlink.net/~pjburke1/cg.htm
This locates the mac.
.
And I can't believe you haven't bookmarked the site!
For shame!
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Old Apr 19, 2002, 10:12 AM
God is good
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Banjul
Joined Jan 2001
4,246 Posts
Quote:
Originally posted by Sparky Paul
. . . . For shame!
OK, it's bookmarked. BTW, most useful . . . . thanx

VP
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Old Apr 19, 2002, 11:30 AM
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Northern New Mexico
Joined May 2001
140 Posts
Here's one that you can use in Excel. It will also help in calculating the twist (or washout) for stable flight.

http://members.webpathway.com/patrul...ng_calc_1a.zip
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Old Apr 19, 2002, 11:46 AM
Registered User
London Ont. Canada
Joined Sep 2001
64 Posts
Thank you All

SP I know, I know.

You have have all been a great help!

Now do you include the control surfaces in these dimensions?
I haven't made them yet, still working out if I want them to taper
to the inside, or the outside?

Any advice?
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Last edited by D.FLinn; Apr 19, 2002 at 11:52 AM.
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Old Apr 19, 2002, 02:10 PM
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Joined Feb 2002
3 Posts
I suggest going to http://www.b2streamlines.com/Panknin.html and downloading the Panknin twist spreadsheet. It'll tell you the twist and CG for a desired static margin among other things. Make sure you read the usage caveats. BTW, in a flying wing control surfaces are always included as part of the wing dimensions.

Elevons extending far inboard aren't nearly as effective as elevons that remain outboard. The inboard element makes the roll response sloppy. However, for ease of control surface hookup to the servo the surfaces are extended inboard so that the servo can be placed ahead of the CG.

As you get nearer the tip the control surface should be a larger percentage of the chord.
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Last edited by coffey; Apr 19, 2002 at 02:16 PM.
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