Design and Aerodynamic Analysis of a Novel 4+2 Retractable-Rotor VTOL UAV

Unmanned Aerial Vehicles (UAVs) with Vertical Takeoff and Landing (VTOL) capabilities have emerged as essential tools in modern aerial missions that demand both operational flexibility and endurance. However, a persistent design challenge lies in the aerodynamic inefficiencies introduced by exposed lift components particularly during fixed-wing cruise phases. Conventional hybrid configurations, such as quad planes and tiltrotors, often compromise cruise performance due to additional drag and system complexity. This paper presents the design and aerodynamic analysis of a novel 4+2 retractable rotor VTOL UAV that addresses this trade-off. The proposed configuration employs four rotors for VTOL operation two of which tilt forward for fixed-wing propulsion while the remaining two retract into the fuselage during cruise. A complete design methodology is developed, including mission-based sizing, component selection, stability and CG analysis, and the development of a custom rotor folding mechanism. Computational Fluid Dynamics (CFD) simulations were conducted in SolidWorks Flow Simulation to evaluate cruise performance in both unfolded and folded configurations. Results show a 42% increase in lift-to-drag ratio when the rear rotors are retracted, along with a noticeable reduction in drag and improved pressure distribution. These findings validate the aerodynamic advantage of integrating a retractable rotor system in hybrid UAV designs, offering an effective balance between VTOL functionality and cruise efficiency.