A scale model is only a valid stand-in for the full-scale aircraft if the flow over it is dynamically similar — same geometry and α, same Reynolds number Re = ρVc/μ, and same Mach number. Get those right and the measured cl and cd transfer to the aircraft unchanged.
Streamlines from the exact potential-flow solution — identical for model and aircraft
Gauge pressure Δp = p − p∞ along the real chord of each
Cp against x/c — one curve, so the model's coefficients are the aircraft's