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3 Trends in Aerospace Standards in 2021

Posted: Friday, December 18, 2020

As we close out 2020 and look ahead to 2021, what are the top trends facing the aerospace standards community? Experts from our aerospace standards development group convened to discuss where their attention will focus in the new year.

Electrification is impacting the entire aerospace industry. Small UAS are electrically powered and carry electrical actuators, sensors, and payloads. Moving up in scale, the industry is looking to operate fully-electric airplanes and electric vertical takeoff and landing (eVTOL) aircraft that promise the carriage of passengers and cargo be done with lower noise, lower operating costs, lower emissions, new design configurations (such as distributed electric propulsion) and new flight control methods. And at the top of the scale, large transport aircraft are transforming conventional subsystems to more electrical subsystems, along with hybrid electric propulsion. 

What all this means is that traditional engine-driven pumps, pneumatic systems and hydraulic systems are making way for electrified propulsion systems—either all electric or hybrid-electric—that can perform the similar tasks. To support these industry efforts, the SAE E-40 Electrified Propulsion Committee is not only setting the standards for new electrified propulsion systems, but also identifying important safety considerations.

With greater demand for electrical power comes requirements for higher voltages far exceeding those in aircraft currently in production. Higher voltages are not without challenges, however. The SAE AE-7 and AE-8 Committees are focusing their attention on developing standards required to meet the performance and safety considerations of high voltage electrical systems and components. The subcommittees within deal with electrical machines, electrical systems, power management, distribution, energy storage, charging, protective controls, electrical system modeling, wiring, cables and connectors. An entry primer on these efforts is AIR6127: Managing Higher Voltages in Aerospace Electrical Systems.

SAE’s AE-7D committee is hard at work looking into energy supply. The committee published AIR6343: Design and Development of Rechargeable Lithium Battery Systems for Aerospace Applications and AIR6897: Battery Management Systems for Rechargeable Lithium Batteries Used in Aerospace Applications, and are developing two standards for charging interfaces (plugs), which will deliver energy to recharge the batteries before flights. AE-7D anticipates a common charging interface standard for smaller normal category aircraft and a separate standard for charging commuter and transport category aircraft: AS6968: Connection Set of Conductive Charging for Electric Aircraft and AIR7357: MegaWatt and Extreme Fast Charging for Aircraft, respectively.

Autonomous System Safety
Automation plays a role in aviation safety for manned and unmanned aircraft systems (UAS). UAS rely heavily on automation through sensory feedback and direct manipulation of controls. Thanks to advancements in sensors, computation and control algorithms, the pace of UAS automation is accelerating, but human interaction still exists on both ends of the spectrum.

Any efforts on aerospace system design and safety assessments have likely been impacted by SAE’s S-18 Aircraft and Systems Development and Safety Assessment Committee, and its ARP4754: Guidelines for Development of Civil Aircraft and Systems and ARP4761: Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, two standards that are generally accepted by global aviation authorities as a means of compliance to rules for aerospace system design and safety assurance for more than two decades. ARP4754 provides recommendations for the safe development and design of aircraft and systems, taking into account aircraft functions and operating environments. ARP4761 presents guidelines for performing safety assessments of civil aircraft, systems, and equipment, particularly when addressing compliance with certification requirements. 

These documents, along with a host of others currently published and in-development, are widely accepted for manned aircraft. The proliferation of UAS has prompted the S-18 committee to identify shortcomings related to specific technical aspects needed for UAS development. To lead these efforts, S-18 established the S-18UAS Autonomy Working Group. The committee’s first document, AIR7121: Applicability of Existing Development Assurance and System Safety Practices to Unmanned Aircraft Systems, is intended to identify specific gaps in both ARP4754 and ARP4761 processes that affect UAS development, the domains where the gaps should be filled, and provide a common understanding of necessary guidance needed to support development assurance and system safety for both developers and regulators. 

The UAS industry is swift and dynamic, so the efforts of the S-18UAS working group is important to both industry and regulators for enabling safe UAS integration into the national and international airspace. These are global efforts, working jointly with EUROCAE WG-63 Complex Aircraft Systems on SAE/EUROCAE documents: ARP4754A/ED-79A and ARP4761/ED-135, along with the SG-1 Applicability of Existing Development Assurance and System Safety Practices to UAS and VTOL.

Additive Manufacturing & Advanced Materials
Additive manufacturing (AM) is intriguing for aerospace because it enables complex yet extremely lightweight designs. The primary challenge, however, is the integrity of the part. Given that safety is of the highest priority in the aerospace industry, considerable research has been conducted on the final parts as well as the feedstock material and the build process itself. 

The three main focus areas within AM are: the machine, the material and the software. Machines are moving towards larger build chambers, more stable processes, faster throughput—via multi-lasers and higher temperatures—and organizations continue to look at the automation of powder handling and reuse. From a materials perspective, research is focusing extensively on powder alloys that are specifically designed for AM. While high-end R&D involves nanoparticles, the aerospace community is concentrating on developing commodity material-properties databases to aid adoption. The software focus bifurcates into the internal workings of the machines —such as in-situ processing monitoring and adaptive control—and post-build modeling and simulation (M&S). Two particular challenges for aerospace are to understand fatigue and damage tolerance (F&DT) of parts and qualifying the "effects of defects" related to the AM build process.

SAE AMS-AM has been developing standards relating to both material and process. The materials research has been instrumental to providing guidance for key aerospace materials, such as titanium, superalloy, high-strength steel and aluminum. Nearly 30 process specifications—such as powder reuse—are works in progress, as the efforts continue to help outline a path for part qualification and the basis for a "fix process" necessary to provide airworthy parts.