How to find center of garvity of giant scale fixed wing plane.?

I’ve a giant scale fixed wing plane which I would like to convert to quad-plane VTOL.
so, I have to find the c.g. of my fixed-wing plane before it was converted to VTOL

Please recommend knowledging about solution and equipment for find c.g.
this is my airframe:

To measure the current c of g, either.
Balance it on two points under the wing moving it for and aft till it sits level, or if it’s not strong enough to take this pressure under the wing them measure the weight on the mains and tail then calculate the balance point in between… this is how it’s measured on full size

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Break out your favorite spreadsheet program for the computation.

  1. The “zero” point for this calculation will the front end of the prop screw
  2. Put a mark on the wing where your C.G. should be
  3. Measure back to the front landing gear from the zero point and center that point under the middle of the strut - call it “F”
  4. Measure back to the rear landing gear from the zero point, center that point under the middle of the strut - call it “R”

Now you have 2 points to weigh the airframe

Open a new spreadsheet. What you’re doing is multiplying the “arm” - distance from the Zero point(to F and R), by the weight, results in a “moment”. Put your scale under the front gear and weigh it. (I usually try to keep the frame level, so block up the gear you’re not weighing)
So, F * WT = Moment. Then do the same thing with the rear after weighing - R * WT = Moment

Then add the 2 WTs. That will be your gross airframe weight.

Add the 2 Moments together.

Next to last is divide the Total Moment by the Gross Weight.

This result is your airframe C.G.

Last is adjust weight within the airframe to get the C.G. near your wing mark.

Yes thats the calculation method by weighing the mass on the gear, for a model the size of what was pictured im sure it would withstand being supported on something under the wing though and just move it till it balances and mark the balace point and measure