Drag Reduction by Wingtip-Mounted Propellers in Distributed Propulsion Configurations

Tip-mounted propellers can increase wing aerodynamic efficiency, and the concept is gaining appeal in the context of hybrid electrical propulsion for greener aviation, as smaller and lighter electrical motors can help with mitigating structural drawbacks of a tip engine installation. A numerical study of tip propeller effects on wing aerodynamics is herein illustrated, considering different power configurations of a Regional Aircraft wing. A drag breakdown analysis using far-field methods is presented for one of the most promising configurations, and a comparison between drag reductions obtained with a tip propeller or a standard winglet installation is also provided. Numerical flow simulations using Finite Volume Methods with actuator disk models are compared with results of a Vortex-Lattice Method, and far-field aerodynamic force calculation is performed for different mesh sizes. A wing drag reduction up to 6% (10%) is predicted under typical cruise (climb) flight conditions when wingtip-mounted propellers take over half of the total thrust usually provided by turbo-prop engines installed at inboard wing position. Drag breakdown analysis confirmed that the observed benefits mainly come from a reduction in the reversible drag component, increasing the effective wing span efficiency.