ron12901

I used the CG calculation links at the top of this forum and I got different Ideal CG's from thom the programs by Adamore and Geistware. From Adamore with a 15 % static margin I got an Ideal CG of 5.08 in.; with Geistware for the same wing/tail numbes the 15% static margin CG was 5.49 in. MY wing has a 17.25 root(12.25 tip); this seems to be a significanr difference. Which program do you use?

da Rock

Geistware was the first I found and I haven't used the other one simply because Geistware always worked well.

CG really isn't something that has to be extremely accurate. In fact, our method of discovery usually has more error than the small difference between the two applications.

Since most modelers choose to go nose heavy, the accuracy is really not important at all for them. They often 'balance nose down' and that's absolutely not accurate. In fact it throws away any accuracy possible.

wellss

I don't use either program, but in looking at them, Adamore seems better. As far as I can tell, Alasdair Sutherland's neutral point or tail volume calculations don't factor in downwash and assume the same aspect ratio for both tail and wing ( same lift slope ). Of course, this would not be correct. The Adamore program has 3 different stabilizer efficiencies to choose from, although I'm not sure how they are derived. In your case, the CG that is further forward would be the better place to start anyway.

Villa

I use either one, and believe both give good accuracy. I usually make slight CG adjustments after a few flights as needed to make the plane fly as I believe it should. I recall that about 10 years ago I designed my first Pusher Canard and used at least two published programs/methods for locating the CG. I was not happy with the results because they were different. I then made up my own formulas, basically shooting for equal loading of the Canard and the main wing, and came up with the CG located between the two results I had calculated from the two other methods. I stayed with my method and then made slight CG adjustments as determined my the way the plane was reacting in flight.

edsplane

If you want to determine the CG accurately for any kind of wing, go to the www.rcaeronauts.com website and get a good idea of the factors involved. The proposed method includes Sutherlands considerations and also the effects of wing tips and neutral point location, on the CG location.