Flight performance optimization of a multi-lift rotorcraft formation

A numeric optimization is performed for maximizing the cruise performance of a multilift rotorcraft system. The optimization process locates the optimal relative positions of the formation rotorcraft. The optimization problem is formulated as a constrained nonlinear programming problem. Constraints on the distances between the formation rotorcraft are imposed in order to maintain safe separation distances. It is shown that for every airspeed an optimal formation geometry can be found that minimizes the rotorcraft power required. Optimization analysis for subsequent airspeeds yields an optimal recommended airspeed that is close to the “bucket” airspeed of the unloaded rotorcraft. Cable length is shown to have a secondary influence on optimization results. The resulting improvement in the performance of the multi-lift system is demonstrated using nonlinear simulations. It is shown that the operational efficiency of the system can be significantly increased by adopting the optimization results.