This paper aims to present an integrated rotorcraft conceptual design and analysis framework, deployed for the multidisciplinary design and optimization of regenerative powerplant configurations in terms of rotorcraft operational and environmental performance. The proposed framework comprises a wide-range of individual modeling theories applicable to rotorcraft flight dynamics, gas turbine engine performance, and weight estimation as well as a novel physics-based, stirred reactor model for the rapid estimation of gas turbine gaseous emissions. A multi-objective particle swarm optimizer (mPSO) is coupled with the aforementioned integrated rotorcraft multidisciplinary design framework. The combined approach is applied to conduct multidisciplinary design and optimization of a reference twin engine light civil rotorcraft modeled after the Airbus-Helicopters Bo105 helicopter, operating on representative mission scenario. Through the implementation of a multi-objective optimization study, Pareto front models have been acquired, quantifying the optimum interrelationship between the mission fuel consumption and gaseous emissions for the representative rotorcraft and a variety of engine configurations. The acquired optimum engine configurations are subsequently deployed for the design of conceptual rotorcraft regenerative engines, targeting improved mission fuel economy, enhanced payload range capability, as well as improvements in the rotorcraft overall environmental impact. The proposed methodology essentially constitutes an enabler in terms of focusing the multidisciplinary design and optimization of rotorcraft powerplants within realistic, three-dimensional operations and toward the realization of their associated design trade-offs at mission level.