quote:

ORIGINAL: Rfabbre

The best, easiest way is to use the "Vanessa CG Machine". They are a snap to make and work great. Check this site. http://home.mindspring.com/~the-plumber/Vanessa%20CG%20Machine.htm

Don't let the instructions scare you. There really is nothing to it.

Be sure you use a small level so you you get the plane horizontal (level).

Here are a couple of pics of one of my planes suspended on the Vanessa. You can't see it, but I put a small mark on the fuselege where the GC is susposed to be. When the plane is level, the plumb bob points to the GC. Just move around some weight (probably batteries) to get the plumb bob pointing at your mark.

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quote:

ORIGINAL: whitedog4491

This is a very good way to do it. I have a Excel spread sheet all set up for this method of doing it, Just enter your values in the proper cells and it shows the correct weight. You can use either metric or pounds and ounces. works the same.

From ****s. Apparently this is the method used on full size




This method is how I go about checking CG on a plane that weighs too much to put on a CG machine. This is generally the same way full scale planes are balanced. You can’t go lifting a 747 by your fingers!


First, have the plane assembled as RTF, but minus fuel. Find a place where you can put the nose of the plane up against a wall. Take a level and prop up the tail wheel until the fuselage is sitting level. You will probably have to take the hatch off in most cases to find a suitable area to set the level on.

Once the plane is sitting level, place masking tape under the area where the main wheels are touching the surface and draw a line where the wheels contact the tape. Make an index mark where the center of the tailwheel falls in the same manner. This mark will be on whatever you propped the tail up with. (I use magazines). It’s also a good time to measure from the wall, to the point where the recommended CG is. Save that number for later.

What you are looking for at this point is the distance to each wheel from the tip of the spinner. (which should be touching the wall at this point) I use a long straightedge to get the distances

As an example, let’s say you come up with theses numbers:
LH main – 22”
RH main – 22”
Tailwheel – 70”

Now, place a scale under each wheel individually. You will have to re-adjust the height of the other wheels each time to keep the plane sitting level. Add more magazines as necessary. (If you have three scales you can get the weights at the same time but make sure the plane is level)
Don’t forget to re-install the hatch before you weigh each wheel. You will wind up with three weights, one for each wheel.

Let’s say you come up with these numbers
LH main – 9 lbs
RH main – 9 lbs
Tailwheel – 5 lbs

Now its just a simple math problem to find where the CG sits right now on the plane.

Weight x ARM (distance) = Moment
22x9=198 in-lbs
22x9=198 in-lbs
70x5=350 in-lbs

Now add the total of all the moments and the total of all the weights.
Weights 9+9+5 = 23lbs
moments 198+198+350 = 746

Then divide the total moments by the total weights.
746 divided by 23 = 32.43

That number 32.43 is "in inches" how far back from the tip of the spinner to where the plane balances right now.
Compare that to the distance that you measured earlier to the recommended CG location.
If you are off one way or another adjust items then recalculate the weights. The distances (or ARM's) arent going to change so you already have those numbers

quote:

ORIGINAL: Rfabbre

The best, easiest way is to use the "Vanessa CG Machine".