4D Trajectory Management of All-Electric VTOL Aircraft

Ph.D. Thesis

Research Motivation

The unique operational characteristics of all-electric vertical takeoff and landing (VTOL) aircraft, along with anticipated increased traffic densities and high operational tempos, may strain the traditional human-managed trajectory management systems. To effectively manage the increased complexity of these flights, this research introduces a 4D trajectory management framework. The framework consists of two key components: 1) a pre-flight planning module for creating flight trajectories prior to departures and 2) an in-flight replanning module for dynamically revising the planned trajectories during flights.

Key Idea

The proposed framework integrates two primary planning systems—pre-flight planning and in-flight replanning:

1. Pre-flight planning module: This module features a pre-flight planner activated before aircraft takeoff, designed to optimize collision-free 4D trajectories for multiple eVTOL operations.

• The planner ensures safe separations, navigates around obstacles (e.g., restricted airspace, terrain, etc.), and continuously monitors the battery energy state.

• The planner is built upon the Mixed-Integer Linear Programming (MILP) optimization, augmented with lithium-ion battery modeling.

2. In-flight replanning module: This module includes an in-flight replanner and a diversion decision-making tool, both activated during flight or when a diversion is declared due to any off-nominal situations.

• The in-flight replanner uses Model Predictive Control (MPC) to rapidly update their intended trajectories in response to the dynamic operating environment.

• The decision support tool evaluates and selects the best diversion destination from a set of potential candidates.

Results: Framework Demonstration

The results illustrate the optimized 4D trajectories for both single and multiple eVTOL flights, highlighting VTOL aircraft with distinctive flight segments (i.e., vertical takeoff/landing and transition) and with varying performance and battery characteristics.

1. Trajectory optimization of a vectored-thrust eVTOL (Joby S4-like) flight:

Optimal trajectory of vectored-thrust eVTOL aircraft (i.e., Joby S4-like)

Detailed airspeed and powertrain information

2. Trajectory optimization of multiple eVTOL flights:

Optimal trajectories of diverse eVTOL aircraft

Results: Use Cases (2D Case)

The city of Miami is selected as the place of demonstration of the proposed system. The following three operational scenarios are presented to prove various functionalities of the framework.

1. Case Study 1: UAM normal operations

An UAM operator generates two flight plans between the same origin and destination except for assigning different cruise altitudes to coordinate with other airspace participants.

2. Case Study 2: Off-nominal Scenarios of Aerodrome Disruption

The pre-flight planning creates an initial flight plan. After a few minutes elapse after take-off, an onboard pilot is contacted by the PSU such that the planned vertiport is closed due to an emergency. The pilot decides to divert and implement the contingency planning system to find which is the best diversion destination.

3. Case Study 3: Off-nominal Scenarios of In-flight Medical Emergency

While the UAM follows an initial optimal trajectory heading to the destination, a passenger suddenly suffers a medical emergency in the air and must be escorted to a nearby hospital for urgent treatment.

Relevant Publications

• S. Kim, C. Justin, and D. Mavris, "Development of 4D Trajectory Optimization Framework for Urban Air Mobility Flight Management" (In Preparation)

• S. Kim, C. Harris, C. Justin, and D. Mavris, "Optimal Trajectory and En-route Contingency Planning for Urban Air Mobility Considering Battery Energy Levels," AIAA Aviation, June 2022. https://doi.org/10.2514/6.2022-3415