Streamlines of smoke particles flow past the mounted projectile
model; drag and lift are computed from the model's shape and
yaw angle, the same measurements a real wind-tunnel balance
records from strain gauges holding the model in the airflow.
Drag = ½·ρ·v²·A·Cd
Lift = ½·ρ·v²·A·Cl(α)
Re = ρ·v·L / μ
- Airspeed — velocity of the wind tunnel flow over the model.
- Angle of attack — yaw of the projectile relative to the airflow; larger angles increase both drag and lift up to stall.
- Projectile shape — streamlined, blunt-nose or finned — each has a very different Cd.
Wind-tunnel testing is how real ballistics programmes measure
drag tables for new shell designs before ever firing a live
round — the resulting Cd(Mach) curve feeds directly into
trajectory-calculation software.