HI BOYS: HOW I CAN CALCULATE THE CG FOR A SIMITAR AIRPLANE

Which one?
Simitars come in all shapes..
They all use about the same c.g., though, 12% m.a.c.
The shape determines where the m.a.c. will be.
root chord:
tip chord:
leading edge sweep:
span:

For a really oddball wing planform, I would be tempted to simply build a simple hand-launched glider of cardboard, and play around with paperclip noseweights until I get a good glide with just a tiny bit more incidence in the wing than in the stab. Airfoil is unimportant - a flat plate will tell you all you need to know about the correct CG. This approach saves a lot of laborious calculations that would otherwise be required, such as dividing the wing into a number of sections, and calculating the center of aerodynamic pressure of each section, then finding the overall center of aerodynamic pressure. Who needs that kind of work?

Oh to be a boy again, the things I would do differently........

Thin foam from a meat tray or similar grocery item works nicely for CG location purposes. Like Rotaryphile I have done the small glider thing for a lot of airplanes and it has been fairly accurate, certainly enough for test flights to be made without crashing.

The last one I did was a 4 inch span IFO model because I had rebuilt the larger one (not much to do on that model) and forgot to write it down anywhere.

If I remember right the Simitar is a flying wing design by Evans. It should work OK with that. The bigger the glider the better though.

For a really odd planform of any sort, take a planform picture with a digital camera, print it, copy that to the thin foam, and proceed with glide tests.