I used to have a software program for rockets, when I was into high power rocketry.
It would calculate CG as well as speed at any given point in flight and expected altittude and was reasonably accurate when compared to the results from my onboard equipment.
That was a complicated software program based on simple strait forward rocket designs and complete known thrust curve data from the motors.
An airplane is much more complex and would require an even more complicated program to calculate.