Aerodynamics' Influence on Performance in Human-Powered Vehicles for Sustainable Transportation

The problem of transport-related greenhouse gas (GHG) emissions is common knowledge. In recent years, the electrification of cars is being prompted by many as the best solution to this issue. However, due to their rather big battery packs, the embedded ecological footprint of electric cars has been shown to be still quite high. Therefore, depending on the size of the vehicle, tens -if not hundreds- of thousands of kilometres are needed to offset this burden. Human-powered vehicles (HPVs), thanks to their smaller size, are inherently much cleaner means of transportation, yet their limited speed impedes widespread adoption for mid-range and long-range trips, favouring cars, especially in rural areas. This paper addresses the challenge of HPVs speed, limited by their low input power and non-optimal distribution of the resistive forces. The article analyses dissipation sources from rolling resistance, aerodynamics, inertia, and more for various vehicles, emphasizing the fundamental role of aerodynamic resistance for HPVs. It is here shown that, for classical non-enclosed bicycles, aerodynamic resistance is typically much higher than rolling resistance, and possibly higher than any type of dissipation during rural trips. Enclosed HPVs, specifically velomobiles, are then proposed as a solution. Their low drag results in a distribution of the various sources of dissipation more similar to that of a car than that of a bicycle. Furthermore, their use in tandem for long rural trips is shown to be particularly efficient, exceeding the 40 km/h threshold with only 75 W/rider and negligible battery consumption. Urban trips, with heavy traffic, may favour non-faired bicycles over velomobiles. However, the latter remain valuable in average-to-low traffic conditions and offer a decisive advantage when the weather is non-optimal.