Relative air density, often denoted as σ (sigma), is a dimensionless parameter used in the field of flight mechanics and aerodynamics to describe the density of air at a certain altitude compared to the density of air at standard sea-level conditions. It’s an important concept when analyzing aircraft performance, especially in relation to lift, drag, thrust, and engine performance.
σ=ρ/ρslρ
- σ (sigma): Relative air density.
- ρ (rho): Actual air density at a specific altitude.
- ρsl (rho_sl): Standard sea-level air density.