An eVTOL (electric Vertical Takeoff and Landing) aircraft is an emerging class of battery-powered vehicles capable of taking off vertically, flying long distances, and landing vertically using electric propulsion. Designed for urban air mobility, cargo transport, and regional flight, eVTOLs have attracted global attention, with hundreds of companies racing to bring their designs to market while securing significant investor funding. However, many of these designs have faced criticism for poor technical viability. In this article, we’ll outline key rules of thumb to help you assess an eVTOL design’s efficiency and feasibility.