HYDRA - Hybrid Design and Rotorcraft Analysis


Fig. 1: Sample configurations studied using HYDRA

HYDRA is a framework designed to analyze and conceptually design vertical take-off and landing (VTOL) configurations for conventional and unconventional configurations. This project is co-developed with Ananth Sridharan and is under constant development to improve the underlying physics and include physics based approaches to model the subcomponents, such as drivetrain models (to allow for engine based, battery based and hybrid propulsion) or finite element analysis for structural analysis of airframe.





Fig. 2: Flowchart depicting the sizing process using HYDRA with the ability to fuse higher-fidelity analysis

The first problem is called preliminary sizing. The four main vehicle characteristics (weight, size, performance and fuel) are interdependent and must be determined simultaneously to ensure that the design is consistent with the parameters chosen. Given a fixed payload, mission and some combination of design parameters, an initial guess for vehicle weight is chosen, and fixed-point iterations are performed until the design characteristics converge.

The second problem can be tackled with multi-variable design optimization, or parametric sweeps. The challenge with preliminary sizing is that the response surfaces are typically non-convex, and global optimization tools add another layer of complexity and require their own specialized fine-tuning of tolerances and error bands for each problem set.  HYDRA is capable of both approaches; factorial search and a multi-discplinary optimization (MDO) framework.

Furthermore, the intention is reduce the computational cost of HYDRA so that sweeps of the entire parameter space of design variables can be done in a time sensitive manner, and the code structure is modular for future developments. By writing the numerically intensive routines in Fortran and wrapping it with Python, distinct modules are created that can be used as plug-and-play units in the Python framework. The code suite also makes use of native Python libraries, such as the the optimization routines.

A more detailed look at the various calculations that occur in preliminary sizing is given below.


The framework of the MDO Simultaneous Analysis and Design (SAND) is shown below where the requirement of all sub-disciplines are handled through constraints and or dsign variables


These tools have been used to study a variety of configurations across various studies. More information on HYDRA can be obtained from this page or some of the publications given below. The framework is in constant development with multiple physics model and numerical techniques being explored and added.


  • Govindarajan, B., and Sridharan, A., "Analysis of UAV Configurations for Package Delivery Missions using Conceptual Sizing," Journal of Aircraft, Vol. 57, No. 6., pp. 1,170-1,188, 2020. DOI: 10.2514/1.C035805

  • Sridharan, A., Govindarajan, B., and Chopra, I., "Scalability Study of the Multirotor Biplane Tailsitter using Conceptual Sizing," Journal of the American Helicopter Society, Vol. 65, No. 1, pp. 1-18, 2020. DOI: 10.4050/JAHS.65.012009

  • Beals, N., Singh, R., and Govindarajan, B., “Conceptual Design of UAS Configurations with Dissimilar Rotors,” 76th Forum of the Vertical Flight Society, October 6-8, Virtual Event, 2020

  • Sridharan, A., and Govindarajan, B., “Evaluation of Sizing Strategies for eVTOL Configurations,” 76th Forum of the Vertical Flight Society, October 6-8, Virtual Event, 2020

  • Govindarajan, B., and Sridharan, A., “Evaluation of UAV Configurations for Package Delivery Missions through Conceptual Design,” 45th European Rotorcraft Forum, Warsaw, Poland, September 16–19, 2019

  • Sridharan, A., Govindarajan, B., Nagaraj, V. T., and Chopra, I., “Design Considerations of a Lift-Offset Single Main Rotor Compound Helicopter,” American Helicopter SocietyAeromechanics Design for Vertical Lift, San Francisco, CA,January 20–22, 2016.

  • Govindarajan, B., Sridharan, A., and Chopra, I., “A Scalability Study of the Multirotor Biplane Tailsitter using Conceptual Sizing,” Proceedings of the 74th Annual Forum of the American Helicopter Society, Phoenix, AZ, May 14–17, 2018.

  • Govindarajan, B., Sridharan, A., and Avera, M., “Integration of Physics Based Weight Models into Rotorcraft Design Sizing,” 43rd European Rotorcraft Forum, Milan, Italy, September 12–15, 2017.