There is growing, perhaps booming, commercial investment in electric vertical takeoff and landing (eVTOL) vehicles that will serve the new urban air mobility (UAM) aerospace market. Upstart and established companies are in a race to develop platforms that can bring about an age of civilian, commercial, and military mobility that enables users to break free of terrestrial limitations and move freely about the sky.
Many aircraft for the new UAM market are in development independently, with large and small aerospace companies reaching out to our experts. Thermal management is a specific technology in demand where Parker Aerospace has deep experience and is now helping multiple UAM companies.
The United States Air Force recently launched the Agility Prime program, a “a non-traditional program seeking to accelerate the commercial market for advanced air mobility vehicles.” The program will enable the more rapid development, testing, and certification of eVTOL platforms – which Agility Prime calls “orbs” – for both civil and military use. The applications that Agility Prime cites for orbs include logistics and sustainment, medical evacuation, firefighting, disaster relief, search and rescue, and humanitarian relief operations.
Going beyond its car-based ride-sharing beginnings, Uber is engaged in the civilian and commercial side of developing eVTOL aircraft – and the required infrastructure for aerial ride sharing – through its Uber Elevate team. Its aircraft development efforts are underpinned by strategic partnerships with several leading aircraft manufacturers. Recently Uber Elevate was acquired by competitor Joby Aviation with a goal to leverage the work of both companies.
Further, eVTOL aircraft development is independently underway with a number of the world’s biggest names in aerospace.
Transporting people with these vehicles creates a new mode of transportation that will connect between commercial air travel and automobiles. Yet moving goods with eVTOL vehicles, even with unmanned drones, may have a larger impact on our society. Cargo delivery drones require the same engineering and the same regulatory conditions, without people, however with the conventions needed and infrastructure to support regular flight. Widespread implementation of delivery drones will prove the systems and processes needed for like vehicle power management, communication, landing locations, and support infrastructure.
Among the propulsion systems being considered for eVTOL applications, distributed electric propulsion (DEP) has emerged as the likely configuration for UAM applications. DEP relies on multiple electric motor-driven rotor-type propulsors distributed across the aircraft to provide vertical lift, thrust, and flight control.
Though DEP system-equipped vehicles will take advantage of the maneuverability afforded them by the technology, DEP systems pose unique challenges for the heat management of the electric motors, electric controllers, and battery packs necessary for their operation.
The electric motors that drive the multiple rotors are arrayed around the aircraft, located in proximity to the rotors. These motors variably generate heat as they perform their propulsive duties, creating a need for effective thermal management to ensure optimal efficiency and motor life. Reducing weight is an important benefit of electric motors. Besides being environmentally friendly, the system for an electric motor has a dramatic weight reduction compared to traditional hydraulic motor systems. Lighter aircraft changes the flight profile and how the aircraft flies, allows for more passengers/cargo and provides more flexibility for other aircraft systems.
Electronic controllers are required to provide the digital commands that govern rotor speed and position, which enable an eVTOL’s ability to climb, descend, and navigate in airspace. These digital controllers take full advantage of the ongoing advancements in semiconductor manufacturing that permit more and more computational power in smaller footprints, giving rise to higher heat levels and heat densities that must, in turn, be removed from the controllers themselves.
The battery packs that provide the electricity needed to power the motors generate heat as energy is released for use by the aircraft. There is significantly higher power demand placed on the batteries at takeoff and landing, which results in a variable thermal management requirement across the vehicle’s flight profile. The aircraft’s thermal management system must be responsive to this variability.
The key to successfully managing the heat generated by DEPs lies with a thermal management system (TMS) with the ability to collect heat in one location then transport it to a place where it can be safely rejected or dissipated. Such systems consist of three major elements:
• Heat collection components – such as liquid flow through cold plates or liquid-cooled enclosures
• Transport components – consisting of pipes, hose, connectors, and pumps
• Heat rejection/dissipation equipment – Heat rejection or dissipation equipment, or heat exchangers
• Controllers to coordinate and manage the system entire thermal dissipation of the system
Designing an efficient and size, weight, and power (SWaP) solution requires access to a wide-ranging portfolio of components and subject matter experts experienced in fluid and thermal management. A previous blog article from the Parker Aerospace Gas Turbine Fuel Systems Division’s thermal management team details the criteria for selecting a thermal management system supplier.
“Because SWAP is such a key challenge with an airborne end use, thermal management needs to be a common design feature of every component and sub-system in electric or hybrid-electric aircraft.”
— Michael Humphrey, business development manager for thermal management solutions, Gas Turbine Fuel Systems Division of Parker Aerospace
It should be noted that heat density and precise location that needs to be the primary focus when assessing an entire thermal management system. Frequently, heat “spreading” – or a reduction in thermal density – is the first stage of creating a solution. Many materials and control components are capable of operating efficiently at extreme temperatures. Thus, reducing thermal density may allow a passive solution, such as heat dissipating into a large thermal mass, to be employed. Other TMS challenges include:
Thermal management has widespread impact across these vehicles, integral with other technologies such as:
The thermal management team at the Parker Aerospace Gas Turbine Fuel Systems Division offers proven thermal management system-level experience developing solutions for demanding environments, including applications for advanced defense and intelligence gathering systems employing technologies that create exceptional thermal density challenges.
“With the DNA of an engineering-focused problem-solving culture, Parker’s TMS team offers the ability to optimize system performance with SWaP-focused solutions while maintaining aircraft safety, applying Parker’s full understanding of the needs of the regulatory authorities. Contributing further to this is Parker’s corporation-wide strength in the areas of materials – including composites – and the availability of subject matter experts to address any aspect of engineering at the component and sub-assembly level.”
— Michael Humphrey, business development manager for thermal management solutions
As the development, testing, and certification of eVTOL platforms accelerates, so too will the demands placed on the thermal management systems needed for these exciting vehicles. As a proven TMS solutions provider, Parker is looking forward to assisting its customers in meeting these coming challenges, helping to bring about a new age of civilian, commercial, and military air mobility.
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This blog was contributed by Jeff Melzak, engineering manager for thermal management solutions, Gas Turbine Fuel Systems Division of Parker Aerospace.