I don't think you are giving enough information. If you know what model it is, you should be able to get a manual on-line for it. Then just follow the manufacturers recommendation for CG. If it is a small airplane such as .60 to .90 size, you should just be able to use your fingers (placed per manufacturers recomendation) to see if the CG is correct.

I have flown everything from .40 size trainer to 33% giant scale and have never owned or needed a CG machine. If you get near the midrange of manufacturers recommendation the airplane should fly fine. Then slowly change the CG forward or aft for your flying style.

Reference post #6: Squaring the wing and calculating CG is not that simple since it is a bi-plane, you have to take into consideration that it is a ultimate and has 2 wings and the wings are staggered.