gzeno

My Feedback: (7)

I have had many ideas thrown at me on how to get the CG of an airplane and the latest is measure from outer edge of wing to inner tip across the wing and multiply by the with of the wing for the total sq inches and that works fine. Now I'm told to divide the total number of sq inches by (3) and what ever that number is take 25% of it as one number and then 33% of it for the second number and the CG is between those numbers. Example would be 300sq inches of wing divided by three is 100. now 25% of 100 is 25 or 2.5 inches and 33% of 100 is 33 or 3.3 inches making the center of gravity between 2.5 inches and 3.3 inches approximately 2 and 3/4 inches from the leading edge. does anyone agree with this process or is there an easier way?

Tall Paul

There are probably more difficult ways to do that, I'm someone will mention at least one...
Wing area.. has no part in the situation!
The wing's -chord-... from leading edge to trailing edge is measured.
The c.g. is placed at the desired point on that chord.
10 inch chord, 33% c.g.... is at 3.3 inches back from the leading edge.
Now determining where the specific chord -is-, is the tricky part, if the wing isn't the traditional Hershey Bar shape.
For a normal wing, this site has the information you will need..
http://www.palosrc.com/instructors/cg.htm

jrpnde

Is this CG value for a particular plane or for general info?? If it's for a certain plane, use the manufacturer's recommendation for a starting. Some start at the main spar and adjust forward or back from there. Others use the percentage of chord as described in one of the other posts.

3DFanatic

My Feedback: (5)

33% of the MAC

tony w

I'm interested in this too. I've almost completed a 50 size 3D funfly from a plan with no CG markings. I've never flown anything like this before so I have no experience of CG settings on such a plane. I have these questions.

1. What % MAC is a good starting point for someone flying a 3D machine for the first time?
2. What % MAC would I be likely to need to get good 3D funfly performance?
3. Do I count the ailerons in or out when measuring the chord? Since the ailerons are huge it makes a big difference.

Tony

DBCherry

My Feedback: (4)

Tony,
1) 25 to 33%
2) Depends on plane and pilot, but 33 to 40% probably
3) Count the ailerons.
Dennis-

tony w

Thanks Dennis, that's just what I wanted to know.

Tony

feihu-RCU

The graphic method is a simple way of finding the MAC for a wing that has a chord which is constant, tapered and/or swept. Once the MAC is found. the desired % of CG is located on the MAC. (The CG location can then be projected to the fuselage if balacing at the root chord is desired.)