Formula for balancing at the CG, based on distance from CG???

[Michael in Toronto]

Is there a (not too complicated) mathematical formula for figuring out how much weight should be added or lightened in order to balance at the balance point based on distance forward or rearward from that point?

For example, if a model needs 1 oz of added weight at the nose - say 12 inches forward of the balance point - to balance properly, how much weight should be removed instead from the tail - say a point 2 feet rearward of the balance point - in order to balance properly?

[Ollie]

It's the same formula you should use to balance a seesaw (teeter totter). The weight times the distance on one side has to be equal to the weight times the distance on the other side. BTW, a force (weight) times a distance at right angles to the force is called a moment or torque.

Example: There is a plane that weighs 10 ounces and balances 2 inches behind the desired CG location. The moment required to move the CG forward two inches is two inches times ten ounces, equals 20 inch-ounces. If the balancing weight is to be located five inches in front of the desired CG location then the balancing weight has to be 20/5=4 ounces so that the moment of 20 inch-ounces is 4 ounces times 5 inches.

The general equation for static balance is: the sum of all the moments about a given point is zero. In this equation the clockwise moments are given one sign and the anticlockwise moments are given the opposite sign. In the above example 0 = 10x2 - 4x5 where the given point is the desired CG location.

[Michael in Toronto]

That works for me. Thank you.

[Mike Taylor]

I had to work those problems in flight school. Stop by your local airport's FBO and ask an instructor. They can show you and example in their flight manuals that show exactly how it is done...

[MikeSt]

http://www.rcgroups.com/forums/showthread.php?s=&threadid=55347

Another example.