Part 3 – “For supersonic aircraft operating at speeds similar to the X-59 (Mach 1.4-1.8), aluminium alloys will likely remain the primary material for large sections of the airframe,” Kalea Texeira, National Training Program Manager at Federal Aviation Administration

Step into the final leg of our enlightening journey with Kalea Texeira, where the spotlight turns once more to aluminium but not as the old guard of aerospace materials. Instead, as Texeira compellingly reveals, aluminium re-emerges from the X-59 program as a vital force shaping the future of flight. Far from being left behind in the age of advanced composites and high-temperature alloys, aluminium proves it still has plenty of lift.

Read the full interview below for her complete insights. Missed the first two parts? Catch up on Part 1 & Part 2 by clicking the link here!

AL Circle: Do the technologies developed for the X-59 have commercial or military crossover potential, particularly in future green aviation platforms?

Kalea Texeira: The technologies developed and validated through NASA’s X-59 Quiet Supersonic Technology (QueSST) program possess significant commercial and military crossover potential, particularly as the aviation industry increasingly prioritizes green aviation platforms. The X-59’s primary innovation—the ability to achieve quiet supersonic flight— has far-reaching implications beyond its immediate research objectives.

Commercial Crossover Potential:

• Revitalization of Commercial Supersonic Travel: The most direct commercial application is the potential to re-establish and expand commercial supersonic passenger travel. By demonstrating that sonic booms can be reduced to a gentle "thump," the X-59 aims to provide the data necessary for regulatory bodies to lift current restrictions on supersonic flight over land [25]. This would unlock vast new markets for high-speed air travel, significantly reducing transcontinental and transoceanic flight times. Companies like Boom Supersonic and others are actively pursuing commercial supersonic aircraft, and the X-59’s success could directly inform their designs and accelerate their market entry.
• Advanced Aerodynamic Design Principles: The X-59’s unique aerodynamic shaping, which manipulates shockwaves to minimize noise, offers valuable insights for future aircraft designs. These principles could be adapted for other high-speed commercial aircraft, potentially leading to more efficient and quieter designs, even for subsonic aircraft, by optimizing airflow and reducing drag.
• Enhanced Passenger Experience: Beyond speed, the ability to fly supersonic without disruptive noise could lead to a more comfortable and acceptable travel experience for both passengers and those on the ground, fostering greater public acceptance of high- speed air travel.

Military Crossover Potential:

• Stealth and Low-Observable Applications: The core technology of sonic boom reduction is essentially about controlling and mitigating pressure waves. This has direct parallels with stealth technology, which seeks to reduce an aircraft’s radar, infrared, and acoustic signatures. While the X-59’s focus is on audible noise, the understanding gained in shaping an aircraft to control shockwaves could be applied to military platforms to reduce their acoustic footprint, making them harder to detect or track, particularly at supersonic speeds.
• Next-Generation Reconnaissance and Strike Platforms: Future military aircraft, especially those designed for high-speed reconnaissance or rapid strike capabilities, could benefit from low-boom technology. The ability to operate supersonically over land without generating a detectable sonic boom would provide a significant tactical advantage, allowing for faster response times and reduced risk of detection.
• Advanced Flight Control Systems: The sophisticated flight control systems and avionics developed for the X-59 to manage its unique aerodynamic characteristics and maintain stability at supersonic speeds could be adapted for other advanced military aircraft, enhancing their performance and manoeuvrability.

Relevance to Future Green Aviation Platforms:

The crossover potential is particularly strong in the context of future green aviation platforms:

• Sustainable Supersonic Flight: As the aviation industry moves towards net-zero emissions, future supersonic aircraft will need to integrate not only low-boom technology but also sustainable propulsion systems (e.g., SAFs, hydrogen, electric). The X-59 provides the critical noise piece of this puzzle. Its success can accelerate the development of truly sustainable supersonic platforms by removing one of the major environmental barriers.
• Material Science Advancements: While the X-59 primarily uses aluminium, the research into its structural response and thermal management at supersonic speeds contributes to a broader understanding of materials under extreme conditions. This knowledge is valuable for the development of lightweight, durable materials essential for electric and hydrogen-powered aircraft, where weight reduction is paramount for range and efficiency.
• Integrated Design Approaches: The X-59 project exemplifies an integrated design approach where aerodynamics, propulsion, and acoustic considerations are deeply intertwined. This holistic engineering philosophy is crucial for developing future green aviation platforms, which must balance performance with environmental impact across multiple vectors (noise, emissions, fuel efficiency).

In conclusion, the X-59 is more than just a quiet supersonic demonstrator; it is a catalyst for innovation across the aerospace spectrum. Its technologies are poised to inform the next generation of both commercial and military aircraft, especially as the industry collectively strives towards a more sustainable and environmentally conscious future.

Kalea Texeira: Based on the learnings from the X-59 Quiet Supersonic Technology (QueSST) program, aluminium’s role in the next generation of supersonic and, increasingly, hypersonic aircraft is poised for evolution rather than obsolescence. While advanced composites and high- temperature alloys will undoubtedly gain prominence, aluminium will continue to be a critical material, adapting to new design paradigms and performance requirements.

Continued Dominance in Primary Structures (Supersonic):

For supersonic aircraft operating at speeds similar to the X-59 (Mach 1.4-1.8), aluminium alloys will likely remain the primary material for large sections of the airframe. The X-59’s successful demonstration of a low-boom design using conventional aviation-grade aluminium reinforces its viability. The benefits of aluminium—its excellent strength-to-weight ratio, well-understood manufacturing processes, reparability, and cost-effectiveness—are compelling for commercial applications where large-scale production is a factor. The evolution here will involve:

• Advanced Aluminium Alloys: Development of new aluminium-lithium (Al-Li) alloys or other advanced aluminium alloys that offer improved strength, stiffness, and fatigue resistance while maintaining or reducing density. These alloys can contribute to further weight savings and enhanced performance without a radical shift in manufacturing infrastructure.
• Hybrid Structures: Increased integration of aluminium with advanced composites in hybrid structures. This allows designers to leverage the best properties of each material—aluminium for its isotropic properties and ease of joining, and composites for their anisotropic strength and tailored stiffness—optimising weight and performance in different sections of the aircraft.
• Additive Manufacturing (3D Printing) of Aluminium: The increasing maturity of additive manufacturing for aluminium alloys could revolutionize how complex aluminium components are produced. This allows for optimized geometries, reduced part count, and integrated functionalities, leading to lighter and stronger structures.

This is particularly relevant for intricate internal support structures or specialized aerodynamic surfaces.

• Evolving Role in Hypersonic Aircraft: Hypersonic flight (typically Mach 5 and above) presents significantly greater challenges, primarily due to extreme aerodynamic heating. While traditional aluminium alloys have temperature limitations, there are still evolving roles for aluminium:
• Cooler Sections and Internal Structures: Aluminium will likely be used in the cooler sections of hypersonic vehicles, such as internal structural elements, fuel tanks (especially for cryogenic fuels like hydrogen), and components not directly exposed to the highest thermal loads. Its excellent thermal conductivity can also be an advantage in certain thermal management systems.
• Thermal Management Systems: Aluminium could play a role in advanced thermal management systems, such as heat exchangers or active cooling channels, where its high thermal conductivity is beneficial for dissipating heat away from critical areas.
• Lightweighting Subsystems: Even if not used for the primary hot structures, aluminium will be crucial for lightweighting various subsystems, including landing gear components, internal equipment racks, and secondary structures, where weight savings still contribute significantly to overall vehicle performance.

Learnings from X-59:

The X-59’s primary learning for aluminium’s future role is not about discovering new material properties, but rather demonstrating how existing, well-understood materials can be innovatively applied within radical new aerodynamic designs to achieve groundbreaking performance. The X-59 shows that conventional aluminium, when combined with sophisticated design and manufacturing, can be at the forefront of aerospace innovation.

This reinforces the idea that the future of aerospace materials is not solely about exotic new substances, but also about maximising the potential of established materials through intelligent design and advanced processing.

In essence, aluminium’s evolution will be characterized by its continued presence in primary structures for supersonic applications, its strategic use in cooler sections and subsystems for hypersonic vehicles, and its integration into hybrid material solutions, all driven by advancements in alloy development, manufacturing processes, and intelligent design informed by projects like the X-59.

Kalea Texeira: The global imperative for sustainable aviation and the ambitious targets for net-zero emissions are fundamentally reshaping aircraft design and material selection. In this transformative landscape, aluminium is poised to maintain, and in some areas expand, its critical role in next-generation aircraft, particularly electric and hydrogen-powered planes. Its inherent properties align well with the demands of these emerging propulsion technologies, though its application will evolve.

Aluminium's Enduring Advantages:

Aluminium’s established advantages—high strength-to-weight ratio, excellent corrosion resistance, good formability, and recyclability—make it a compelling material for future aircraft. For electric and hydrogen-powered planes, weight reduction is even more paramount than for conventional jet fuel aircraft. Batteries are inherently heavy, and hydrogen, whether stored cryogenically as liquid hydrogen (LH2) or in gaseous form, requires robust yet lightweight containment. Every kilogram saved in the airframe directly translates to increased range, payload, or energy efficiency.

Role in Electric Aircraft:

• Structural Components: Aluminium will continue to be a primary material for fuselage, wing structures, and other airframe components where its lightweight properties are crucial for offsetting the weight of heavy battery packs. Advanced aluminium alloys, including those with improved fatigue resistance and higher strength, will be favoured.
• Thermal Management: Electric aircraft generate significant heat from batteries, power electronics, and electric motors. Aluminium’s excellent thermal conductivity makes it ideal for heat sinks, cooling plates, and integrated thermal management systems to ensure optimal operating temperatures for these critical components.
• Motor and Generator Casings: Aluminium alloys are well-suited for the casings of electric motors and generators due to their lightweight nature and ability to dissipate heat efficiently.

Role in Hydrogen-Powered Aircraft:

Hydrogen propulsion, whether through fuel cells or direct combustion, introduces unique material challenges, particularly concerning hydrogen storage and embrittlement.

Aluminium is expected to play a significant role:

Cryogenic Fuel Tanks (LH2): For liquid hydrogen, which must be stored at extremely low temperatures (-253 °C or -423 °F), specialised aluminium alloys (e.g., 2219, 5083) are already proven materials for cryogenic tanks in space applications. Their ability to maintain ductility and strength at cryogenic temperatures, combined with their lightweight nature, makes them strong candidates for aircraft LH2 tanks.

Fuel Cell Systems: Aluminium can be used in the balance-of-plant components for hydrogen fuel cell systems, including heat exchangers, piping, and structural supports, where lightweight and corrosion resistance are important.

Structural Integration: The overall airframe for hydrogen aircraft will still require lightweight materials, and aluminium will continue to be a primary choice for the main structural elements, integrating seamlessly with the hydrogen storage and propulsion systems.

Evolution and Challenges:

While aluminium’s future is bright, its evolution will involve:

• Advanced Alloys and Manufacturing: Continued development of new aluminium alloys that offer even higher performance, better fatigue life, and enhanced resistance to specific challenges like hydrogen embrittlement. Advanced manufacturing techniques, such as additive manufacturing, will enable the creation of optimised, lightweight aluminium structures with complex geometries.
• Hybrid Material Systems: Increased use of hybrid structures combining aluminium with composites and other advanced materials to achieve optimal performance for specific parts of the aircraft. For instance, composite outer skins might be paired with aluminium internal structures.
• Recyclability and Circular Economy: Aluminium’s high recyclability rate (it is infinitely recyclable without loss of properties) makes it a highly sustainable material. This aspect will become increasingly important in a circular economy model for aviation, further cementing aluminium’s long-term viability.

In summary, aluminium is not merely a legacy material; it is a future-proof material for next- generation aircraft. Its inherent properties, coupled with ongoing advancements in alloy development and manufacturing, position it as an indispensable component in the transition to electric and hydrogen-powered aviation, supporting the industry’s ambitious net-zero emissions goals.

AL Circle: Do you see opportunities for aluminium use expanding into new areas of aircraft design, such as in battery casings or lightweight support structures?

Kalea Texeira: Absolutely. Beyond its traditional role in primary airframe structures, aluminium is poised for significant expansion into new and critical areas of aircraft design, driven by the ongoing revolution in propulsion systems and the relentless pursuit of lightweighting. The opportunities are particularly pronounced in the context of electric and hydrogen-powered aircraft, where efficient energy storage and distribution are paramount.

Battery Casings:

This is a prime area for expanded aluminium use. As electric aircraft become more prevalent, the demand for robust, lightweight, and thermally efficient battery casings will skyrocket.

Aluminium offers several key advantages for this application:

• High Strength-to-Weight Ratio: Batteries are heavy, and minimizing the weight of their enclosures is crucial for aircraft performance. Aluminium alloys provide excellent structural integrity without adding excessive mass.
• Thermal Management: Lithium-ion batteries generate heat during charge and discharge cycles. Aluminium’s high thermal conductivity is invaluable for dissipating this heat away from the battery cells, preventing overheating and ensuring optimal performance and safety. Aluminium battery cases can be designed with integrated cooling channels or fins to enhance thermal regulation [30].
• Corrosion Resistance: Aircraft operate in diverse environments, and battery casings need to withstand potential exposure to moisture and other corrosive elements. Aluminium’s natural corrosion resistance provides a durable protective enclosure.
• Electromagnetic Shielding: Aluminium can also provide a degree of electromagnetic shielding, which is important for protecting sensitive battery electronics from external interference and preventing interference with other aircraft systems.
• Recyclability: The ability to recycle aluminium from end-of-life aircraft into new battery casings (or other components) aligns perfectly with circular economy principles and sustainability goals in aviation.

Lightweight Support Structures:

Aluminium’s role in lightweight support structures is also set to expand, particularly for integrating new systems and optimising internal layouts:

• Internal Equipment Racks and Mounts: As aircraft incorporate more advanced avionics, sensors, and power electronics, lightweight yet rigid structures are needed to house and support these components. Aluminium alloys are ideal for fabricating custom racks, brackets, and mounts that minimize weight while providing necessary structural support and vibration dampening.
• Hydrogen System Integration: For hydrogen-powered aircraft, lightweight support structures will be essential for securing cryogenic tanks, fuel cells, and associated plumbing. Aluminium’s properties make it suitable for these specialized supports, especially where thermal expansion and contraction need to be managed.
• Seating and Cabin Interiors: While not a new area, there is continuous innovation in lightweighting cabin components. Advanced aluminium alloys and manufacturing techniques can lead to even lighter seat frames, galleys, and overhead bins, contributing to overall aircraft weight reduction and fuel efficiency.
• Actuator Housings and Subsystem Components: Many smaller, critical components within an aircraft, such as hydraulic or electric actuator housings, pump bodies, and valve manifolds, can benefit from lightweight aluminium construction, especially when manufactured using advanced techniques like additive manufacturing to optimize their geometry and reduce material usage.

Advanced Manufacturing Techniques:

The expansion of aluminium into these new areas will be significantly enabled by advanced manufacturing techniques, such as:

• Additive Manufacturing (3D Printing): Allows for the creation of highly complex, optimized geometries that are impossible with traditional manufacturing, leading to significant weight savings and integrated functionalities for battery casings and support structures.
• Friction Stir Welding and Advanced Joining: Enables stronger, lighter joints for aluminium structures, reducing the need for fasteners and further optimizing weight.

In conclusion, aluminium’s versatility, combined with ongoing advancements in metallurgy and manufacturing processes, positions it as a material with expanding opportunities in aircraft design. Its ability to meet the stringent demands for lightweighting, thermal management, and structural integrity makes it indispensable for the next generation of electric and hydrogen-powered aircraft, particularly in critical areas like battery casings and specialized support structures.