By Steve Belknap
Here is a simple tool you can use to find the CG for any airplane. It is especially useful when designing your own plane. You can use it to give the estimated CG while the plane is still only on paper. The .pdf file is an Excel worksheet. Simply download it and start filling in numbers. I did not create this and I would cite the source if I could remember where I got it.
The first step is to determine a ‘Datum’. This is an arbitrary location along the longitudinal axis. Data-wise it really does not matter where you choose although it is usually better to choose a location that will not change during your design, such as a firewall or leading edge bulkhead. Now decide if you want positive numbers to go for or aft. In the example all measurements to the rear of the datum will be positive and all measurements to the front are negative. Use whatever units you like.
Determine the weight units you like.
Measure, or estimate, lengths and weights and enter them into the calculator. All measurements are from the datum. You will measure to the CG of each item such as a battery or wing. When designing a plane you might have dozens of items. You can have a separate entry for every piece of the plane. The location of the CG will be instantly calculated at the bottom. The number given is a length measured from your datum. The total weight for the airplane is also given.
