Delivering aircraft and various avionics compliant with the latest standards and regulations is increasingly difficult. Today, it’s not uncommon for a single commercial aircraft to comprise hundreds of line-replaceable units, hundreds of miles of wire, and unique configurations throughout all parts of a platform that must meet numerous certification requirements. With increasing electrical system content and complexity, a single change during the design, verification, or compliance process can put the entire program in jeopardy. With the rise in electrification and design complexity, aerospace original equipment manufacturers (OEMs) need to look for new methodologies to mitigate compliance risk.
Key Aerospace Industry Trends
Two key trends are shaping the aerospace industry. First, increasing mission demands are escalating platform performance requirements. Whether it’s extending the twin-engine range of commercial aircraft or enhancing the use of remotely controlled drones, OEM customers demand greater mission capability.
The second trend is electrification. Platform developers increasingly implement the functions that enable this greater mission capability electrically. These electrically enabled capabilities include auto-land and In-flight Entertainment (IFE). Further, electrical approaches are replacing mechanical, pneumatic, and hydraulic implementations of existing functionality; for example, Fly-by-Wire systems, Electronic Flight Instrument Systems (EFIS), and Combined Vision Systems (CVS) have become commonplace. It’s no surprise that More Electric Aircraft (MEA) has become a dominant theme in commercial and defense aircraft today.
Although the aerospace industry has made great strides in introducing electronic and electrical systems into modern platforms, it has driven platform power demand to new levels. Statistics reveal there is a 10x increase in power consumption over the past 50 years for today’s modern aircraft (Figure 1). Increased power generation and integrated electrical technologies in aircraft provide a multitude of capabilities such as airline passenger entertainment systems and USB ports for device use and recharging; however, these electrical applications increase the aircraft’s power consumption.
Complying with Performance and Certification Requirements
On the commercial side, aerospace OEMs must meet the regulations associated with Type Certification. Likewise, defense platform providers must demonstrate that they satisfy the performance requirements associated with Customer Acceptance. The fact is, delivering aircraft on time — and meeting all performance and certification requirements — is more difficult today because of so much complexity.
Current methods used to meet aircraft certification are woefully inadequate. Many of the approaches aircraft manufacturers and their suppliers employ today were developed back in the era of simple electrical systems. These outdated approaches are slow, tedious, and often rely on the physical exchange of information. Key data is handed off from one team to another in a fragmented way where multiple drawings, documents, Excel spreadsheets, and databases are used. Further, data is often re-entered manually to conduct verification checks and analyses.
The complexity of advanced electrical systems coupled with manual transcription errors can lead engineers to incorrectly analyze or overlook key portions of the design. Often, these missed elements are not discovered until peer review or after certification package submission when the electrical system is largely complete. This can lead to significant and costly design iterations, program delays (including aircraft redesigns), re-integrations, and modifications of existing aircraft — ultimately impacting aircraft revenue and time-to-market milestones. Finally, report generation is a long, tedious manual process, often conducted manually with spreadsheet-based tools.
What’s needed is a new methodology for compliance analysis, design validation, and reporting that readily enables development staff to meet electrical compliance requirements and effectively demonstrate it.
MIL-E-7016F Military Standard
Military standard MIL-E-7016F focuses on methods and analysis of electrical load and power source capacity for aircraft across specific flight phases. This standard observes the load impacts (bus load) and source capacities for all flight phases. MIL-E-7016F also evaluates AC and DC bus loading to ensure the connection of all essential systems while minimizing load iteratively. This includes a variety of aircraft bus types: AC buses for motors, fuel pumps, and anti-ice heating; DC buses for avionics, in-flight entertainment, and maintenance computers; battery buses for standby equipment such as critical “continued safe flight” essential equipment; and Ram Air Turbine (RAT) buses for emergency power generation.
Although it was prepared for the Department of Defense (DoD), the MIL-E-7016F standard is now tailored for commercial aircraft applications, evaluating the worst-case electrical load combinations for all phases of flight. Figure 2 illustrates the flight phases, from ground maintenance, start, warm-up, and taxi, to takeoff and climb, cruise, then descent and landing — even during an emergency situation.
SAE-AS50881 for Commercial
On the commercial side, SAE-AS50881 covers all areas of aerospace vehicle selection, design, and installation of wiring, wiring devices, harnesses, optical cabling, and termination devices. This specification was developed to provide wiring system safety, performance, reliability, and lifecycle management, covering all types of aerospace vehicles including helicopters, unmanned airplanes, and missiles. The standard describes design requirements, particularly for the installation of wire harnesses, and a methodology to describe the derating of a wire in a wire bundle (segment of wire harness) to ensure the safety of the aircraft design.
Today’s aircraft must be designed so power sources function properly when they are connected or independent. System voltage and frequency at terminals of all essential equipment must be maintained within the limits for which they were designed during any operating condition. This standard ensures that the aircraft can be operated safely under Visual Flight Rules (VFR) for no less than five minutes using normal electrical power systems at the maximum certified altitude. Parts of the electrical system may remain on if there is a single malfunction and must not result in a loss if turned off or on, and must be electrically or mechanically separate and isolated from the parts that are turned off.
Electrical Load Analysis (ELA)
Electrical Load Analysis (ELA) is extremely important for assuring the safety and correct operation of aircraft. An electrical load is the electrical component or part of a circuit that actively consumes electric power such as electronic equipment and lights. ELA estimates the electrical system load capacity of an aircraft to determine if the system can provide sufficient source capacity to operate under any flight conditions. This is achieved by evaluating the load demands under various aircraft flight phases. Just as weight and balance must be examined when equipment is added to or removed from an aircraft, the ability of the aircraft’s electrical system to safely provide power for added equipment must be assured.
ELA is performed by adding all of the electrical loads applied to the electrical system during operating flight phases. Power sources must provide enough power to support electrical equipment and associated power requirements. Design teams must analyze each generator, rectifier, battery, and bus for each flight phase and deliver a report to demonstrate regulatory compliance.
Addressing Complexity and Mitigating Risk
Guided by MIL-E-7016F, the Capital Load Analyzer from Siemens represents a new approach to conducting electrical load analysis accurately and quickly in a way that is scalable, automated, and continuous. Analysis execution is so rapid that designers can apply it immediately as they iterate and explore the electrical system’s design. In addition, by interrogating the configuration-controlled electrical digital twin (Figure 3), Load Analyzer ensures that the right version of the electrical system design is always evaluated. Together, these maximize platform innovation while reducing program risk.
By directly accessing the digital twin, users can generate a number of analyses at the touch of a button, accelerating the needed verification. More importantly, a user can check on how a specific change impacts the electrical load and power management every time a modification or new exploratory iteration is added — in real time. This means teams involved in all aspects of electrical system design can check, analyze, and virtually verify system power sourcing as the design evolves (Figure 4). Teams no longer have to wait to see if they have load management issues at integration. Rather, users can find out about issues early in the program, as the design is conducted.
To demonstrate the electrical system’s compliance, users can quickly create reports from templates (Figure 5). These templates can pull in live design data, analysis tables from specific elements, analysis charts of loads during specific time intervals, and more. The templates can also pull in third-party data. This makes it easy to create the evidence necessary to demonstrate compliance. Also, any time the design or analysis results change, these reports can be automatically regenerated, updating all of the report data with no manual re-entry. This saves engineers’ time, making them more likely to meet their program milestone commitments.
As the industry moves to More Electrical Aircraft, today’s engineers require advanced, automated electrical load analysis methods to keep up with the increasing complexity and rapid change of modern aircraft electrical systems. A new methodology, such as Siemens Capital Load Analyzer, exploits direct access to the electrical system digital twin to ensure accurate results, accelerate execution, and ensure that the current, correct version of the aircraft design is evaluated. Using automated report generation populated with analysis results that can be traced back to each design artifact, users can more rapidly demonstrate compliance and meet regulatory and performance requirements.
This article was written by Anthony Nicoli, aerospace and defense director for the Integrated Electrical Systems segment of Siemens Digital Industries Software, Plano, TX. For more information, visit here .