Simulating Series Hybrid Tilt-Rotor Aircraft in GT-SUITE

The rise in demand for electric and hybrid-electric aircraft, particularly in the Urban Air Mobility (UAM) sector, has fueled innovation in aircraft powertrain design. One promising configuration is the series hybrid tilt-rotor system, which combines the power and efficiency of hybrid-electric propulsion with the versatile flight dynamics of tilt-rotor technology. In this blog, we’ll dive into the basics of series hybrid tilt-rotor systems, why they’re gaining popularity, and how GT-SUITE, a multi-physics simulation platform from Gamma Technologies, can simulate and optimize them early in the design and development process.

A tilt-rotor aircraft features rotors that can transition between vertical and horizontal orientations, enabling both vertical takeoff and landing (VTOL) capabilities and efficient forward flight. By integrating a series hybrid system (where an internal combustion engine (ICE) drives a generator to supply electrical power to motors that turn the rotors) we can achieve the best of both worlds: the extended range of traditional fuel-powered engines and the flexibility and control of electric propulsion.

Components of a Series Hybrid Tilt-Rotor System:

1. Internal Combustion Engine (ICE): Drives a generator to produce electrical energy, offering high energy density.
2. Generator: Converts mechanical energy from the ICE into electrical energy.
3. Battery Pack: Stores energy to supplement the generator output.
4. Electric Motors: Drive the rotors and facilitate the tilt-rotor’s unique ability to transition between vertical and horizontal flight.
5. Flight Control System: Generates Control Outputs based on the deviation between the target trajectory and the actual flight state.

System Workflow of a Series Hybrid Tilt-Rotor in GT-SUITE

The development and simulation of a series hybrid tilt-rotor aircraft involves tightly integrated subsystems working under closed-loop control to ensure stable and efficient operation throughout the flight envelope. The system architecture and workflow, as shown in the figure, can be described in the following sequence:

System Workflow of a Series Hybrid Tilt-Rotor in GT-SUITE

1. Target Mission Definition

The simulation begins with defining the flight mission profile, which includes:

• Target altitude
• Target velocity
• Desired rate of climb
• Flight states over time

These mission parameters serve as reference inputs for the flight controller to guide the aircraft through various phases like hover, transition, cruise, and descent.

2. Flight Controller

The flight controller continuously compares the current aircraft state with the mission-defined targets. Based on the error between actual and target parameters, it generates control commands such as:

• Elevator deflection
• Nacelle tilt angle (specific to tilt-rotors)
• Throttle setting
• Propeller blade pitch

These outputs ensure the aircraft maintains its trajectory and stability across dynamic flight conditions.

3. Aircraft Body and Motion Calculation

The aircraft body module receives control input and evaluates the dynamic response. This involves:

• Force calculation: Derived from aerodynamics and thrust contributions (including vertical lift in VTOL modes and forward thrust in cruise)
• Equations of Motion (EoM): Motion quantities like velocity, angular rates, and position are updated based on net external forces and moments

This module represents the 3DOF rigid body physics of the aircraft.

4. Electric Propulsion Subsystem

In a series hybrid configuration:

• The electric motor receives commands (e.g., torque or speed setpoints) from the flight controller.
• The motor drives the propeller, generating thrust needed for vertical lift or forward motion.
• The propeller model converts shaft power into aerodynamic thrust using blade element momentum or similar methods.

This closed-loop feedback ensures the thrust output aligns with what is needed for stable flight.

5. System Integration Loop

All subsystems interact in a closed-loop fashion:

• Mission target → Controller → Actuator/motor response → Aircraft body dynamics → Updated flight state.
• The updated state feeds back to the controller, ensuring continuous correction using PID controllers and mission adherence.

Simulating a Series Hybrid Tilt-Rotor Model in GT-SUITE

Let’s look at a system-level example model of a series hybrid tilt-rotor aircraft developed in GT-SUITE. This model integrates electric propulsion components, 3DOF flight dynamics, nacelle actuation, and energy management systems into a unified simulation environment.

The tilt-rotor is modeled to perform a complete VTOL mission, from vertical takeoff through cruise and back to landing, while enabling detailed analysis of powertrain behavior and flight control responses under varying operational modes.

Series Hybrid Tilt-Rotor Model Example in GT-SUITE

To explore the impact of different electrification strategies on flight performance and energy consumption, two distinct simulation cases were studied using a representative mission profile:
Flight Mission Profile
The simulated mission captures a complete VTOL flight cycle, including the following phases:
• Vertical Takeoff
• Transition to Climb
• Cruise Flight
• Descent
• Hover and Landing

Flight Mission Profile

A flight control system governs the nacelle angle throughout the mission. The nacelle starts at 90° (vertical) for takeoff and gradually transitions toward the horizontal (fixed-wing) position during the climb phase. This fixed-wing configuration is maintained during cruise. The nacelle then transitions back to vertical for the descent and hover/landing phases.

Case 1: Series Hybrid Mode
• Power Configuration: The electric motor is supported by a 64 kW hybrid assist during the Climb/Cruise Phase and Descent/Hover Phase, which can be modified accordingly in the ECU Generator controller
This configuration demonstrates how hybrid support can enhance performance and extend operational endurance during peak power demands.

Case 2: Pure Electric Mode
• Power Configuration: Fully powered by a battery-electric system, with no engine assistance.

This case showcases the aircraft’s behavior and energy consumption under pure electric propulsion for the full mission cycle.

Key Metrics and Results in Hybrid Tilt-Rotor Simulation

The simulation results include:
• Battery State of Charge (SOC): Tracks energy consumption and efficiency across flight phases.
• Battery Power Demand: Highlights real-time power draw during different maneuvers.
• Motor Power: Reflects electric propulsion load throughout the mission.
• Flight States: Includes velocity, altitude, and nacelle angle transitions to correlate system behavior with flight dynamics.

Simulation Results

Simulation Result Summary Table

These two simulation cases provide insight into how powertrain configuration and flight phase control impact performance, range, and energy usage for a hybrid tilt-rotor aircraft. The results lay a foundation for further optimization of energy management strategies in hybrid-electric rotorcraft systems.

Series Hybrid Tilt-Rotor Aircraft Simulation Animation

Learn More about Our Aerospace Simulation Capabilities  

To learn more about how GT-SUITE can help you design, simulate, and optimize advanced aerospace systems, visit our Aerospace Industry Page for detailed insights, case studies, and technical resources. For any specific questions, project inquiries, or personalized guidance, don’t hesitate to contact our team of aerospace simulation experts.