Smoke streamlines flow left-to-right past a mounted projectile
model held on a strut, the same setup a real wind-tunnel balance
uses to measure drag and lift with strain gauges.
Drag = ½·ρ·v²·A·Cd
Lift = ½·ρ·v²·A·Cl(α)
Re = ρ·v·L / μ
- Airspeed — velocity of the flow over the model.
- Angle of attack — yaw of the model relative to the flow; larger angles raise both drag and lift up to stall.
- Air density — thinner air (higher altitude) means lower forces for the same speed.
- Shape — streamlined, blunt-nose or finned — each has its own base Cd.