Abstract—The equivalent skin-friction method is widely used for parasite drag estimation during the conceptual design of small Unmanned Aerial Vehicles (UAVs). This study derives a new equivalent skin-friction coefficient for short-range electric mini UAVs using Computational Fluid Dynamics (CFD) simulations of nine representative UAV configurations. The derived coefficient is found to be significantly lower than values commonly adopted in the literature for UAV preliminary sizing. To evaluate its practical implications, the coefficient is incorporated into a conceptual sizing framework and applied to a representative design case. The results show that the use of conventional coefficients leads to systematic overestimation of parasite drag, affecting wing loading, power loading, and overall vehicle sizing. The proposed coefficient provides a more realistic basis for drag estimation and can improve the accuracy of conceptual design methods for electric mini UAVs.

Keywords—parasite drag, equivalent skin friction, Unmanned Aerial Vehicles (UAVs), conceptual design, Computational Fluid Dynamics (CFD)

Cite: Sidi Moulaye Sidi Moulay and Mohamed Elamine Ait Ali, "An Equivalent Skin-friction Coefficient for Parasite Drag Estimation and study of Its Influence on the Conceptual Design of Small Electric UAVs," International Journal of Mechanical Engineering and Robotics Research, Vol. 15, No. 5, pp. 549-556, 2026. doi: 10.18178/ijmerr.15.5.549-556

Copyright © 2026 by the authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).