Cruise Drag Reduction Through Chord Modulation with Application to Distributed Propulsion

An investigation into the effect of airfoil chord reduction on the drag of a fixed-span wing is presented. Chord reduction is characterized within two scenarios: fixed lift and lift coefficient yielding an increasing flight velocity, and fixed lift and flight velocity necessitating a variable lift coefficient. The dependence on chord of the airfoil’s zero lift and sectional pressure drag was established though examination of experimental data for the selected airfoil, a NACA 0012. Analytic expressions are subsequently derived that quantify the behavior of the profile and wing vortex drag. The test case is an aircraft geometry based on a Cessna 210. The analysis shows that for the variable velocity case, both zero lift and sectional pressure drag increase with chord reduction (which requires increased flight velocity), whereas vortex drag reduces significantly. The net result is a reduction in wing drag. For the fixed flight velocity case, chord reduction increases both the sectional pressure drag and the wing’s vortex drag, however, the zero lift drag drops markedly, yielding a net drag benefit. Including the drag contribution of the fuselage and empennage shows that a chord reduction necessitating a higher flight velocity always causes an overall drag increase. For the fixed flight velocity case, a chord reduction still yields a drag reduction, but of lesser magnitude than for the wing alone.