Drag Reduction by Wingtip-Mounted Propellers in Distributed Propulsion Configurations

Abstract

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.

Numerical investigation of aerodynamically efficient wing tip-mounted propeller configuration using coupled RANS–BEM approach

“…Irrespective of the direction of rotation and thrust, stall is observed at AoA = 16° for tip-tractor configuration. Sinnige et al (2019, 2021) and Minervino et al (2022) observed a similar trend in their studies with the propeller at the tip in tractor configuration.…”

“…Having a swirling flow at the tip which has an opposite rotation to the wing tip vortex increases aerodynamic efficiency. Snyder and Zumwalt (1969) (experimental), Miranda and Brennan (1986) (analytical), Sinnige et al (2019) (experimental) and Minervino et al (2022) (computational) used propellers at wing tips in tractor configuration which resulted in reduced induced drag and increased wing aerodynamic efficiency. Sinnige et al (2019) compared the tip-mounted tractor configuration with conventional one and found that inboard-up rotating propeller at wing tip results in better aerodynamic efficiency than the conventional configuration.…”

“…Even though Sinnige et al (2021) conducted a comparative experimental study on the tip-mounted tractor and pusher configurations, flow field and surface flow details were not studied. Stokkermans et al (2019), Kim et al (2021) and Minervino et al (2022) used cost-effective actuator disk methods to study the flows involving propeller. The present study compares the wing with tip-mounted propellers in tractor and pusher configurations.…”

Principles and examples of drag reduction in civil airliners

“…After the takeoff, the propellers will spin, and, by creating a swirl, the high-frequency rotation will act against the wingtip vortex, decreasing both its intensity and the strength of downwash. Moreover, the propeller's advantage (decrease in induced drag) outweighs its potential disadvantage (increase in skin friction drag due to the wing behind the propeller's slipstream) [12].…”

Experimental assessment of aerodynamic and aeroacoustic interaction effects of wingtip-mounted propellers

“…(2019) demonstrated from experimental studies that the reduction in drag promoted by a wingtip-mounted propeller is due to a reduction in the downwash experienced by the wing because of a combination of wingtip-vortex attenuation and swirl recovery that occur with a wingtip-mounted propeller rotating inboard-up. In these conditions, an increase in effective aspect ratio and consequent reduction of induced drag is obtained (COLE et al, 2021;MINERVINO et al, 2022;SINNIGE et al, 2019;SNYDER;ZUMWALT, 1969). In addition, the local increase in dynamic pressure in the portion of the wing washed by the propeller slipstream increases the lift generated (AREF et al, 2018;SINNIGE et al, 2019).…”