Finding the Center of Gravity By James Goss          Have you ever needed to locate the exact center of gravity for your large models? I have a method that allows you to determine your models exact CG location and it is accurate. This method does not require the use of complicated calculus and also does not require hanging your model from a string. Remember that the center of gravity is the sum of the weight of each component of the plane multiplied by the distance of that component from a fixed reference point. So you can see that the CG is determined by the weight of your model and how the weight is distributed. This is why everyone's model, even though identical to another as far as looks, will have its own unique CG location. Two modelers can't build the same plane and have them weigh the same. Everyone builds differently; even you can't build two of your own identical planes and have them weigh the exact same amount.      The manufacture tells us to balance the plane at a certain location and we do without questioning their CG reference point. Quite often they give us the wrong CG location and our planes never fly like they were meant to until we play around with the CG location by trial and error. A little more weight to the nose or a little less to the tail and so on. Of course if we do have the exact CG location for our plane it may still need a fine-tuning after we fly it. This method really pays off when you are trying to balance a large giant scale plane. Some planes do not have the right structural features that will allow you to place them on a balance stand or even pick them up because of their weight. Try to hold a 30-pound plane on your fingertips for a balance check without pushing a hole through the wing. It the proper balance for the plane is on a pipe spar centerline you can suspend it with a rope around the pipe if it has plug in wings, but if it calls for the balance to be 1-inch in front of the pipe you are out of luck again.      It took me a while to interpret the CG definition, but when I did it was as clear as could be. I decided all I have to do is weigh the plane from three main locations instead of weighing every component of the plane, measure these locations from a fixed reference point (the nose or the tail), multiply the distance of each point in inches times the weight at that point in ounces, sum them all up, and divide by the total weight of the plane. I guarantee you that this method will work every time and is very accurate. The three reference points can be the two main wheels and the tail wheel or nose gear, either way will work the same. I will show you an example of how easy it is. It doesn't matter what shape your plane is, it can be a normal looking plane, a round plane, a flat square plane, or any shape you can imagine. In the example I will use the Postage Stamp to show you how easy it is.      All you will need is a small set of weighing scales. For small planes I use a set of post office scales that will weigh up to 5 pounds. Digital scales will be ideal here. The Postage Stamp is a tail dragger so it has two front wheels and a tailskid. Steps One: Set your plane's wheels on some blocks that are the same height as your weighing scales. Step Two: Place a flat sheet of plastic, or anything that will simulate a wall for the nose of the plane to touch. You can actually use a wall, but it will get in the way when you start to measure. I use a two foot square sheet of coroplast and stand it up in front of the plane with the nose of the spinner nut touching. Try to get it square with the leading edge of the wing, not the wheels. Step Three: Assign identities to the three wheels such as RH for right wheel, LH for left wheel, and TS for tailskid. Draw these notations on a sheet of paper in their relative positions on the plane so you will be able to keep up with what is what. Step Four: Remove the blocks from the right wheel and place your scales under the wheel, log the weight measurement in ounces, do the same for the other two wheels. My RW measured 21.5 ounces. The LW measured 20.5 ounces. The TS measured 16.5 ounces. Depending on how your wheel gear are bent you will get different weights. To check, the three should add up to the total weight of your plane. Step Five: Measure each wheel center to the fixed reference point and log the distance in inches. My RW measured 6 inches. The LW measured 5.75 inches. The TS measured 30.25 inches. Step Six:  Multiply the weight in ounces of each wheel by the distance in inches of each wheel from the reference point. Add the three together for a total summation. For my RW the product was 129. For the LW the product was 117.8. For the TS the product was 499. The total sum is 745.8. No unit of measurement, just 745.8. Step Seven:  Divide this number by the total weight of your plane. In my case it was 745.8 divided by 58 ounces. This gives 13 inches to be measured from the fixed reference point. This produces a CG for the Stamp that is 5 ½ inches from the leading edge on the wing.      That's all there is to it, seven simple steps that only takes about five minutes to complete. It is fast and accurate and after you do it one time for practice you will probably agree that it is well worth the effort. Test it on a plane that you know for sure where the CG is suppose to be and you will see that it indeed does work. Remember that this method does not tell you where the GC should be for best performance of your plane; it tells you where the CG is actually located.