They mount the airplane models or parts of an airplane like just a wing, or a rudder in wind tunnels to test their drag and lift, stability, etc.
How do they know where to hang it from or mount it on. How do they estimate the lift center of a new design of a jetliner which has no predecessor to use as a reference.
I am guessing it is a process of trial and error. But there must be an algorithm or method to arrive from an estimate to actual lift center.