Variable rotor speed and active blade twist for civil rotorcraft: Optimum scheduling, mission analysis, and environmental impact

Abstract

The concepts of variable rotor speed and active blade twist constitute promising technologies in terms of improving the operational performance and environmental impact of rotorcraft. Modern civil helicopters typically operate using nearly constant main and tail rotor speeds throughout their operational envelope. However, previous research has shown that decreasing the main rotor speed within salient points of the operational envelope can result in a notable reduction of rotor power requirement, resulting in more efficient aircraft. This work aims to develop an integrated approach able to evaluate the potential improvements in fuel economy and environmental impact through optimum implementation and scheduling of variable rotor speed combined with active blade twist. A comprehensive rotorcraft analysis method is utilized, comprising models applicable to flight dynamics, rotor blade aeroelasticity, engine performance, gaseous emission prediction, and flight path analysis. A holistic optimization strategy comprising methods for Design of Experiment (DOE), Gaussian Process-based (GP) surrogate-modeling, and genetic optimization is developed. The combined framework is used to predict globally optimum variable rotor speed and active blade twist schedules resulting in minimum fuel consumption. The overall method is employed to assess the impact of the investigated concepts for a representative Twin-Engine Light (TEL) helicopter operating within realistic mission scenarios. The optimizations carried out suggest that variable rotor speed combined with active blade twist may result in mission fuel consumption and nitrogen oxides emission (N O x) reductions of the order

On the Effects of Optimal Implementation of Variable Rotor Speed and Power Management on Hybrid-Electric Rotorcraft

“…In this work, the rotorcraft framework has been extended with an efficient optimization strategy targeting to obtain optimum rotor speed and power split schedules for any operating point in the flight envelope. This strategy is an expansion of the approach introduced by Goulos et al [16] and later adopted in Refs. [17,18,40].…”

“…The observed fuel decrease was obtained by varying the rotor speed within a ± 15% range of nominal speed. Goulos et al [16] investigated the concept of VRS in conjunction with Active Blade Twist (ABT) for a Bo 105 helicopter through a multidisciplinary assessment.…”

“…The concept of VRS for rotorcraft has been covered extensively in the literature from an aerodynamic [10,13], coupled aircraft-engine [11,12,14], and mission level standpoint [16,18]. However, no previous work has investigated the potential benefits of VRS concept for conventional and hybrid-electric tilt-rotor, also combined with power management optimization.…”

“…An integrated simulation framework is deployed comprising models for tilt-rotor performance [7,19], mission analysis, gas turbine [20] and battery-motor [21] performance and pollutant emissions prediction [22]. An efficient Design Space Exploration (DSE) and global optimization strategy is employed for the evaluation of optimal controls at aircraft and mission level as reported in [16]. This consists of models for design of experiment, surrogate modeling and genetic optimization.…”

X-ray Computed Tomography Method for Macroscopic Structural Property Evaluation of Active Twist Composite Blades

“…A variety of engineering approaches and active rotor technologies have been devised to alleviate this vibration. One promising concept is the active twist rotor (ATR) scheme, in which the activation of piezoceramic fiber composites built into the blade structure enables the individual pitch angles to be varied according to the desired control effect [1][2][3][4]. The main advantage of ATR technology over other actuation schemes is that the actuator itself is used as a primary load-bearing structure without resorting to any amplification devices.…”