Scaling Laws for Fixed-Wing Single-Engine Electric Propulsion Systems
Hem Lata, Fnu
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The rise of new aircraft propulsion methods (e.g., powered by batteries, fuel cells, or hybrid electric systems), the increased use of automated and integrated flight control systems, and the envisioned use of personal Vertical Take-off and Landing (VTOL) vehicles in urban environments (urban aerial mobility) lead to novel technical and regulatory challenges for aircraft manufacturers, certification authorities and operators. Of primary concern are operational safety and closely connected pilot situation awareness and workload. The Trajectory Energy Management task involves manipulating flight and propulsion controls to achieve a planned flight profile. The key areas to focus on in Trajectory Energy Management are energy, power, and management. This research is intended to define some requirements for energy management such that the pilot can safely accomplish an intended profile and land with enough energy reserves to satisfy the intent of operation rules 91.151 (VFR reserves) and 91.167 (IFR reserves). In the context of trajectory energy management, there is a spectrum of automation tools that may assist the pilot. For example, common avionics systems with moving maps display range rings that help the pilot manage fuel state. These systems make assumptions based on current ground speed, fuel flow, and fuel reserve requirements. Requirements for similar tools that employ electric propulsion do not yet exist and must be defined based on prototype algorithm development, simulation results, and flight test data. This project provides solutions and data to help the FAA develop performance estimation tools, flight safety assessment tools, and the associated means of compliance for Trajectory Energy Management Systems. This research intended to develop scaling laws relating the power and energy consumption by a fixed-wing single-engine subscale model to a full-scale airplane. The research intended to relate the required power and energy consumption to achieve a planned flight profile and sustain the required power and energy consumption for individual trajectory segments. The subscale model used in this research was Albatross by Applied Aeronautics, and the full-scale airplane was Velis Electro by Pipistrel. The power and energy demand data were collected by performing the flight tests on both aircraft with similar flight plan trajectories. The flight trajectory consisted of take-off, climb to an altitude, cruise at a constant altitude, descent, and land. Velis Electro flew with the flight mission, which included take-off, climb to a cruise altitude of 600 feet, then cruise for 10 NM at 600 feet, descent, and land. Albatross data were collected with similar flight missions but with a scaled-down cruise altitude of 160 feet. NASA research paper on "Modelling Flights” describes the geometric and dynamic similitude requirements for free-flight testing. This paper is used extensively as a reference document for calculating the model dimensions for geometric similitude and flight test profiles and environmental conditions required for dynamic similitude. Linear scaling factors based on the wingspan, wing loading, and maximum take-off weight (MTOW)were calculated. These scaling factors were used to scale the power and rate of energy consumption by Albatross. Scaled power and rate of energy consumption were compared with the power and rate of energy consumption of full-scale airplanes. It is found in research that power and rate of energy consumption scaled using the wingspan as scaling factor had the least amount of error for the climb and cruise segment.