Help calculating CG for wing.

[Jus10]

I need help on how the CG should be calculated on a wing with a chord that runs like in the picture below.

http://www.modelaircraft.org/templates/ama/0903_15.asp
This webpage has been the most help so far. Its given me a pretty good idea on how to do the calculatation. The part that is throwing me off is the drastic chord change near the root of the wing. Can someone help? Thanks!

This is my (short) thread on the plane.
http://www.rcgroups.com/forums/showthread.php?s=&threadid=165789

[Jus10]

Anyone?

[Jus10]

Anyone know of where I should repost this or if I can get it moved to another forum that might be able to get an answer... Thanks!

[voyantus]

Not sure if it will really help or not, but I have had a lot of success using this page for finding good CG on home builts.

http://ourworld.compuserve.com/homepages/slope_scale/page17.html

Brian

[Martin Hunter]

I think you'll get better results with this in the Modeling Science forum so I'll move this thread there.

Martin

[Jus10]

Thanks a bunch!!!!

[RSCherry]

I suggest that you start by locating the CG at 25% of the MAC. This will provide for a stable flight position which you can fine tune further back if necessary.

The MAC is the chord line running through the centroid of your wing planform, or you can approximate it by using a graphical technique for a tapered wing and ignoring the "bump" at the root.

Bob

[Ollie]

You can find the mean aerodynamic chord (MAC) of the wing by using the program at:
http://perso.wanadoo.fr/scherrer/matthieu/english/mce.html
The aerodynamic center of the wing is at about 25% of the MAC.
The proper CG is not based on the wing alone but depends on the tail moment arm and the tail area too.

Use the above program to find the MAC of the tail. Its areodynamic center (AC) is also at 25%of its MAC. The tail moment arm length is the distance between the wing AC and the tail AC. The plane's over all AC or neutral point (NP) is at the location where the wing area times its AC distance to the NP is equal to the tail area times the NP distance to the tail's AC.

The CG should be about 5 to 10% of the wing MAC ahead of the NP for initial flight testing.

[Dick Huang]

Jus10,
Here is a program that will tell you where to locate the cg.
Dick Huang:)