I need to find the CG for a swept wing - RC Groups
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Apr 19, 2002, 12:21 AM
Registered User

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

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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Apr 19, 2002, 08:33 AM
Registered User
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.
this helps. If it needs more explaination let me know.
Apr 19, 2002, 11:08 AM
Ascended Master
Sparky Paul's Avatar
This locates the mac.
And I can't believe you haven't bookmarked the site!
For shame!
Apr 19, 2002, 11:12 AM
God is good
Viper Pilot's Avatar
Originally posted by Sparky Paul
. . . . For shame!
OK, it's bookmarked. BTW, most useful . . . . thanx

Apr 19, 2002, 12:30 PM
Registered User
Here's one that you can use in Excel. It will also help in calculating the twist (or washout) for stable flight.

Apr 19, 2002, 12:46 PM
Registered User

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?
Last edited by D.FLinn; Apr 19, 2002 at 12:52 PM.
Apr 19, 2002, 03:10 PM
Registered User
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.
Last edited by coffey; Apr 19, 2002 at 03:16 PM.