Minimising induced drag with weight distribution, lift distribution, wingspan, and wing-structure weight

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Because the wing-structure weight required to support the critical wing section bending moments is a function of wingspan, net weight, weight distribution, and lift distribution, there exists an optimum wingspan and wing-structure weight for any fixed net weight, weight distribution, and lift distribution, which minimises the induced drag in steady level flight. Analytic solutions for the optimum wingspan and wing-structure weight are presented for rectangular wings with four different sets of design constraints. These design constraints are fixed lift distribution and net weight combined with 1) fixed maximum stress and wing loading, 2) fixed maximum deflection and wing loading, 3) fixed maximum stress and stall speed, and 4) fixed maximum deflection and stall speed. For each of these analytic solutions, the optimum wing-structure weight is found to depend only on the net weight, independent of the arbitrary fixed lift distribution. Analytic solutions for optimum weight and lift distributions are also presented for the same four sets of design constraints. Depending on the design constraints, the optimum lift distribution can differ significantly from the elliptic lift distribution. Solutions for two example wing designs are presented, which demonstrate how the induced drag varies with lift distribution, wingspan, and wing-structure weight in the design space near the optimum solution. Although the analytic solutions presented here are restricted to rectangular wings, these solutions provide excellent test cases for verifying numerical algorithms used for more general multidisciplinary analysis and optimisation.</jats:p>

Aerodynamic Modeling of a Flying Wing Featuring Ludwig Prandtl’s Bell Spanload

“…Rearranging Equation ( 6), it is seen that the c(y)C l (y) distribution is simply a scaled version of the Γ distribution. Thus, many readily available outputs from a vortex-lattice method or similar are seen to be the same shape and are simply scaled versions of each other, as indicated in Equation (7).…”

“…This concept has been revisited, such as with an attempt to generalize the bending moment constraint [5]. Additionally, further study by a team at Utah State came to a similar conclusion when predicting the ideal distribution for an aircraft in steady flight [6] and when considering weight distribution across the wing [7]. Recent work has also incorporated viscous effects into a scheme very similar to Jones' work by accounting for airfoil profile drag along the span.…”