On the applicability of the Lock formula for the prediction of transonic wave drag

Kurzfassung

The prediction of wave drag during the conceptual design of transonic transport aircraft is a challenging task, for which the Korn-Lock-Mason is frequently used. Despite its widespread use, this formulation has not been systematically validated against modern supercritical designs. This paper addresses that gap by assembling a consistent dataset of publicly-available wind-tunnel and flight-test measurements. Two limitations of the original formulations are identified: the Korn equation over-predicts the influence of the lift coefficient, and the Lock formula under-predicts the strength of the drag rise above $\mathrm{Ma}_\mathrm{DD}$. The application of the original method to spanwise strips is also shown to smear both the lift and Mach dependencies. To remediate these issues, a modified Korn equation with a free exponent on the lift term is proposed, reducing the root-mean-square prediction error of $\mathrm{Ma}_\mathrm{DD}$ by up to 52 %, and a new Lock-type drag-rise model with steeper exponents captures the measured behaviour substantially better. When combined, the modified equations result in an improved and consistent fit to the experimental data, with the Korn airfoil technology factor as the single calibration parameter, thus remaining sufficiently simple for conceptual-design application.