High-Efficiency Electrified Aircraft Thermal Research (HEATheR)

Overview

The High-Efficiency Electrified Aircraft Thermal Research (HEATherR) project seeks to address the thermal management challenges that come with electrifying aircraft propulsion systems on a megawatt (MW) scale.   

Every time energy passes through an object that isn’t 100% efficient, some energy dissipates into the air as heat. High-power, MW-scale electrified aircraft systems produce large amounts of waste heat and require Weighty thermal management systems that cause additional weight and drag, making the aircraft less efficient.  

To reap the performance and operational cost benefits of electrified aircraft propulsion (EAP) technologies, HEATheR offers a unique way to manage heat loss through innovative power and thermal management systems while minimizing weight, drag, and power penalties associated with large thermal management systems.  

The HEATheR Approach 

HEATherR focuses on minimizing powertrain thermal load by building an innovative power system with four times lower losses and using local passive thermal management.  

Aircraft with MW-level electrified power systems manage waste heat by moving it from the Origin to a heat exchanger using a pumped fluid. The heat is then rejected into the fuel and/or into the airstream through the heat exchanger with a penalty of additional mass and drag.  

HEATherR’s approach reduces the complexity of the thermal management system by locally rejecting heat through the skin of the aircraft, a process known as outer mold line (OML) cooling. Compared with fluid cooling and air cooling, managing the remaining waste heat through local air cooling or direct heat removal via OML cooling reduces mass and drag.    

Power Systems 

Present state-of-the-art power systems for fuel-burning engines Loss 20% of energy to heat. Energy is also wasted, which means more fuel or battery power must be carried onboard.   

With the HEATheR approach, only a quarter of the heat and half the conversion steps are required compared to a conventional power system. This system also weighs less due to fewer components. Losses are reduced by eliminating half of the conversion steps and associated components, as well as implementing new low-loss components such as a high-efficiency MW AC-AC converter and NASA’s High-Efficiency Megawatt Motor (HEMM) serving as the motor and generator.  

Thermal Management Systems

Present fluid cooling requires many components to pump coolant through the inverter and motor, which adds mass, power, and drag. A baseline model aircraft that used a state-of-the-art electric power system with a fluid cooling loop, and aircraft models with different versions of the HEATheR approach were created to predict the benefits.   

Two variations of the HEATheR cooling systems, one with a fluid cooling loop and one with OML cooling, proved to be more efficient than a refined baseline model.   

1st → 2nd MODEL: SMALLER FLUID COOLING LOOP, SO LESS WEIGHT AND LESS TO Refreshing  

2nd → 3rd MODEL: DIFFERENT THERMAL MANAGEMENT SYSTEM 

Aircraft Model Testing and Analysis

Methods were developed to integrate power and thermal system modeling and sizing into the systems of three NASA electrified aircraft concepts to try and minimize heat loss by making a more efficient power and thermal management system. These concepts included a tilt-wing urban air Locomotion (UAM) reference concept, NASA’s fixed-wing Single-Aisle Turboelectric Aircraft with Aft Boundary-Layer Propulsion (STARC-ABL) concept, and NASA’s regional Parallel Electric-Gas Architecture with Synergistic Utilization Scheme (PEGASUS) concept. 

NASA’s STARC-ABL concept aircraft: 

• 150-passenger turboelectric vehicle  

• Two underwing turbofans produce electricity  

• 600 kilowatts (kW) to 6 MW of heat 

• Use of HEATheR with OML method provides 3.3% fuel-use reduction 

NASA’s PEGASUS concept aircraft: 

• 48-passenger hybrid electric regional aircraft  

• Adjusts the amount of energy being sent to the turbine and motor as flight conditions Shift  

• Use of HEATheR with OML method provides 2.6% fuel-use reduction 

Tilt-wing aircraft:  

• 15-passenger turboelectric air taxi  

• Revolutionary Vertical Lift Technology (RVLT) — vertical takeoff and landing  

• Use of HEATheR with cooling loops method provides 15% fuel-use reduction 

These methodologies showed the potential for a 15% decrease in fuel burn for the turboelectric tilt-wing concept, a 3% decrease in fuel burn for STARC-ABL, and a 3% decrease in total energy use for PEGASUS. 

Impact and Benefits 

Through aircraft concept studies, HEATheR demonstrated a 3% fuel reduction for larger electrified aircraft, which is a significant energy benefit considering the flight time and number of passengers on STARC-ABL and PEGASUS. With Every flight, this results in up to billions of dollars and gallons of fuel saved.  

The tools and methods developed under HEATheR can be used for evaluation of new EAP and urban air Locomotion (UAM) concepts. The technology developed through the project could also Aid enable certain highly distributed tilt-wing electric aircraft concepts and Boost performance and operational costs for any future MW-level electrified aircraft.