Endurance Optimisation of Battery-Powered Rotorcraft

Abstract

This paper proposes a technique to extend the endurance of battery-powered rotorcraft by sub-dividing the monolithic battery into multiple smaller capacity batteries which are sequentially discharged and released. The discarding of consumed battery mass reduces the propulsive power required, thereby contributing towards increased endurance. However, the corresponding implementation introduces additional parasitic mass due to the required battery switching and attachment and release mechanism, which, together with the decrease in battery efficiency with decreasing size, results in endurance improvements only being achieved beyond a threshold payload and which scale with rotorcraft size. An endurance model for battery-powered rotorcraft is presented, together with a technique to determine the maximum endurance and corresponding battery combination, by solving the Knapsack Problem by Dynamic Programming. The theoretical upper bound on rotorcraft endurance, which may be obtained from an ideal “infinitely-divisible” battery, is derived from the Breguet-Range Equation. Theoretical derivations and model predictions are validated through experimental flight tests using a popular commercial quadrotor.