MrClean
Well-known member
The easiest way to check airplanes for their current CG that I have found is to hang the airplane in a sling. This method uses a sling made from a loop of some heavy 1/8" chord. My loop is made from a 14 foot piece of chord which makes a diameter of about 4.5 feet. You also need a plumb bob and I made mine from an extra piece of wooden dowel. For a suspension point you can use a nail in an exposed rafter or a plant hook in your ceiling anything that can withhold the weight of your plane. In my example I used a simple piece of chain that is hooked onto a ceiling fan. The Chord loop is wrapped around one part of the airplane, up through the chain suspension point and back down to another part of the plane. Here I have it wrapped around the nose of my F-22 foamy. It then goes through the chain and then wraps around the cutout before the elevators.
Also suspend the plumb bob from the chain between the chords temporarily tying the string so that you can raise and lower the plumb bob. I usually wrap the string around the chain a couple times. My wooden dowel doesn't weigh much so it will hold still. Set your airplane so that it hangs level in flying attitude. Now slide the plumb bob down so that it hangs over the highest part of your fuselage. When everything stops swinging around, the plumb bob will point to the current CG of your airplane.
How's it work? You've essentially made two plumb bobs and both the plumb bob and the airplane will be hanging from the same point and the Center of Gravity of both will be on a line from that point to the center of the Earth's mass. Hang a piece of weight off the tail and the plane will shift a little forward. This will make the plumb bob point a little farther aft, just like it should. The lateral balance of the plane works the same way. Put a piece of weight on the left side, and the plane shifts a little right. In the end, balance your plane by adding weight or moving components so that the plumb bob points to the desired CG of the plane, as in this picture...
And that's all there is to it.
WRC
Also suspend the plumb bob from the chain between the chords temporarily tying the string so that you can raise and lower the plumb bob. I usually wrap the string around the chain a couple times. My wooden dowel doesn't weigh much so it will hold still. Set your airplane so that it hangs level in flying attitude. Now slide the plumb bob down so that it hangs over the highest part of your fuselage. When everything stops swinging around, the plumb bob will point to the current CG of your airplane.
How's it work? You've essentially made two plumb bobs and both the plumb bob and the airplane will be hanging from the same point and the Center of Gravity of both will be on a line from that point to the center of the Earth's mass. Hang a piece of weight off the tail and the plane will shift a little forward. This will make the plumb bob point a little farther aft, just like it should. The lateral balance of the plane works the same way. Put a piece of weight on the left side, and the plane shifts a little right. In the end, balance your plane by adding weight or moving components so that the plumb bob points to the desired CG of the plane, as in this picture...
And that's all there is to it.
WRC
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