Analysis of key elements to evaluate the performance of a multirotor unmanned aerial–aquatic vehicle

Key elements of the design methodology for a hybrid air/underwater vehicle propulsion system are evaluated. This new category of hybrid vehicles can operate both in air and underwater with a single propulsion system. This study emphasizes multirotor electric propulsion systems composed of electric motors, propellers and battery pack. These components need to be chosen to maximize vehicle's range and endurance when flying and swimming. Although a general optimization design methodology is beyond the scope of this work, the method proposed allows setting up first the vehicle physical constraints including weight and payload. Next, the propulsion element characteristics are evaluated. This include optimizing battery pack size and capacity for constrains given, and theoretically evaluating motor–propeller curves in air and underwater to obtain operating parameters including angular velocity, torque, power and efficiency in both mediums. Last, endurance and range is obtained for the operating range in air and water. This methodology allows trade studies and this is illustrated by a simple case study for a fixed size vehicle where different motors, propellers and battery packs are considered. Numerical computations are presented for these elements and compared.