Nomenclature b= half-chord length, m C L , C M = lift and moment coefficients in concentrated form; Eq.(1) C Lα , C Mα ; C Lq , C Mq = lift and moment coefficients caused by a change in the angle of attack and in the pitch rate, respectively; Eq. (6) C lα = lift-curve slope, 1/rad h, α = plunging displacement (m) and the twist angle (rad) about the pitch axis, respectively L , M = unsteady lift per unit length, N/m, and moment per unit length, N, respectively q = pitch rate about the reference axis (≡ 2bα/U ∞ = 2α ) t, τ = time variable (s) and its dimensionless counterpart (≡ U ∞ t/b), respectively U ∞ = freestream speed, m/s ρ ∞ = air density, kg/(m s 2 ) ς = parameter denoting dependence on prior motion history φ L , φ M = aerodynamic indicial lift and moment functions in concentrated form; Eqs. (2) and (3) φ α , φ Mα ; φ q , φ Mq = indicial functions in concentrated form; Eq. (6) ω, k = circular and reduced frequencies (≡ ωb/U ∞ )