The design and manufacture of a new commercial aircraft is extremely complicated, expensive, and risky. The development can cost billions of dollars and last up to ten years before the new plane enters service. Increasing electro-mechanical complexity and density makes aircraft design especially challenging and resource intensive. Electronics govern a majority of the critical systems in next generation planes, like flight control actuation, cabin pressurization, and wing de-icing. The computers, sensors, and wiring needed to connect and control these systems will come to dominate the interior of the airframe. Cabin amenities add even more wiring due to increasing demands for entertainment and communication systems.
Aircraft must also support extensive redundancies to prevent individual system failures from causing catastrophe. The electrical wiring and interconnect systems (EWIS) regulations, set forth by the FAA, outline standards for the design, implementation and maintenance of airplane wiring harnesses. A major component of these regulations is the physical separation and segregation of electrical wires from other systems and from other wiring. This is crucial to achieving safety and redundancy requirements in a plane, and helps prevent failures such as harness chafing, arcing, and electromagnetic interference from damaging or disrupting other systems.
Despite its difficulty, electro-mechanical design and development must adhere to strict schedules. Delays in progress can cost the company millions of dollars in extra development and follow-on effects of late entry into service. What’s more, errors in design can snowball into larger problems when manufacturing begins, further jeopardizing progress. Even small inaccuracies in wire lengths or spacing between bundles can prevent the proper installation of the wire harnesses. This not only adds significant cost but also can delay delivery of aircraft to customers, affecting the company’s reputation and stock price.
There is immense pressure on aircraft design teams to move quickly and hit program milestones. This can erode the motivation to perform extra analysis and validation of aircraft designs before release to initial production. Changes that are made without proper communication between the electrical and mechanical domains can inadvertently introduce EWIS violations into the design. If these go undetected until critical design review, the manufacturer will need weeks or even months to re-design, re-verify, re-release, and then retrofit each plane under construction. Such mistakes are incredibly costly and can put programs, careers, and even companies at risk.
Given the impact of ever-increasing electro-mechanical complexity, how do companies adjust their airplane development process in order to design accurately while meeting tight timelines? The optimal strategy is to use a process that allows for the incremental and digital exchange of ECAD and MCAD design data throughout the design process. Incremental data exchange ensures that the relevant multi-disciplinary features in the ECAD and MCAD platform representations are synchronized at each point in the design. This continual synchronization creates a steady line of communication between the electrical and mechanical engineers, increasing productivity and reducing design errors.
The potential impediments to ECAD-MCAD collaboration are numerous. First is the traditional separation that has existed between the electrical and mechanical disciplines. Electrical and mechanical engineers typically work with completely different tool sets and have completely different vocabularies. Many times, they even reside in different physical locations.
Furthermore, mechanical and electrical CAD systems have different ways of presenting the structure of the same object. MCAD systems might represent an LRU in a physical bill of materials such as the screws, chassis, circuit boards, and connectors. However, an ECAD representation of the same module would include a functional or schematic view that transcends the physical structure of the object. Certain electrical functions can map to several different circuit boards and connectors, making it impractical to associate a single function to a single physical part.
Because of these and other impediments, previous efforts to collaborate have met with limited success. Earlier ECAD-MCAD collaboration tools used everything from sticky notes, and email, to Excel® spreadsheets. These approaches fell far short for obvious reasons. As a result, many aerospace development teams resorted to internally developed software and processes for collaboration that they had to test and verify with each new release of the underlying ECAD and MCAD tool suites. These locally developed software and processes were costly to maintain and required dedicated in-house support.
TRUE CO-DESIGN: CROSS-PROBING
The electrical and mechanical design processes can be more connected, integrated, and collaborative than they are today. Seamless cross probing between the two domains enables closer integration and collaboration by enabling the engineers in each domain to design with contextual information from the other (Figure 3).
Figure 3: A connector is selected in the electrical logic design (left) and then automatically highlighted in the MCAD tool (right)
A key feature of such integration is replacing the cumbersome file-based exchange of previous methods. Integration used to depend on exporting a massive file of changes into a file system for other engineers to retrieve and import. Now, Capital and NX support API level integration, where the two domains connect directly to update the design with changes or new information. Engineers no longer swap files but truly integrate at the data level via a robust mechanism. For instance, a Capital designer may publish a bill of materials for the wiring that NX then seamlessly consumes.
With this integration, design of the electrical system and wiring harness takes place with explicit knowledge of hazardous areas, such as severe weather and moisture prone (SWAMP) areas. Doing so allows the ECAD designer to account for the impact on the electrical performance of these areas when designing the electrical system. On the mechanical side, space reservations can be made and the severity of bends in the harness can be adjusted to account for the wiring bundles that must route through the mechanical structures. With access to this contextual information from other domains, both electrical and mechanical engineers can quickly reconcile incompatibilities between the ECAD and MCAD designs.
In a typical example, the mechanical engineer wants to make sure that the bundle containing all of the necessary wires will route through the allotted physical space. The mechanical engineer does not want to create and manage these wires in the MCAD model, as it would be too difficult and time-consuming. Instead, the electrical definition is created in Capital. The maximum allowed bundle diameter, based on various mechanical constraints, is shared with Capital. By automatically applying design rules, Capital ensures that the wire bundles, composed of synthesized or interactively routed wires, remain within the bundle diameters specified by the mechanical designer. This ensures correct by construction design and avoids costly rework.
In the last few years, the electrical and electronic content in airplanes has expanded while the space available has remained constant. The increase in in-flight entertainment systems, the introduction of in-flight wireless internet, and the move towards electrically operated systems have all increased the amount of wiring necessary to transmit data and power around the plane. Designers must contend with this increase in electrical content while working with the same amount of physical space and maintaining the mandated system redundancy and physical separation. Cross probing and cross visualization between environments enables designers to understand wire routing in 3D space and thus determine the optimal routing.
This electronic expansion will only continue in the future. The more electric aircraft (MEA) concept posits an aircraft that will operate an increasing number of its systems electrically, eventually including the propulsion systems. Such an aircraft replaces the hydraulic, pneumatic, and mechanical operation of various systems with electrical systems. The MEA is expected to increase the efficiency and reduce the weight of the aircraft, resulting in environmental, financial, and reliability benefits. However, because its vast electrical system will govern everything from in-flight entertainment to the actuation of ailerons and landing gear, the MEA will need to possess several layers of electrical redundancy. The wire harness design will therefore be under additional scrutiny as it grows in size and function.
The immense complexity of modern planes results in thousands or even millions of tradeoffs and change orders, impacting cable length, type, and physical placement. A robust change management methodology is paramount to integrated electrical and mechanical aerospace design.
Mechanical design defines the bend radius constraints of the wire bundle based on its physical structure. By communicating these bend radius constraints back to Capital, the electrical engineer can use them to create the formboard upon which the wiring harness will be assembled (Figure 4). With the bend constraints from MCAD, Capital can alert the formboard engineer if they are creating a model that cannot be cost-effectively manufactured.
Figure 4: The formboard provides a full scale drawing of the harness to aid in manufacturing
Even after the harness design is relatively mature, late-breaking design and manufacturing changes can affect the entire system in unpredictable ways. Customer specifications and suppliers’ inability to produce necessary components can result in modifications to the design. For instance, modern aircraft are equipped with hundreds of sensors monitoring both external conditions, like weather and barometric pressure, and internal conditions, like cabin climate and fuel level. Each of these sensors connects to the wiring harness to store and communicate the information they gather. Replacing or moving any of these sensors could spawn multiple change orders for both mechanical and electrical designs that would then need to be verified for cost, weight, and functionality.
The challenge of change management, therefore, is how to track ECAD-MCAD inter-domain changes quickly and efficiently. There are two major aspects of change management. First is the automatic merging of data and the clear display of changes to the designer. Capital is equipped with a robust change management tool that automatically creates a list of changes made to the design (Figure 5).
Figure 5: Incoming changes are clearly displayed for the electrical engineer to review individually
From this list, the electrical engineer can choose to accept or reject each change individually, rather than as a full set of changes. The change management window in Capital is also able to live cross-probe with both the electrical and mechanical designs. As each item is selected in the change management tool, it will be automatically highlighted in either the MCAD or ECAD environments to help the engineer understand the change being proposed. The change manager can also preview a set of changes in a flattened diagram. The flattening may be 3D, orthogonal, or unfolding.
The second critical piece is a change policy that defines whether the electrical or mechanical design is the master of the data and the direction in which changes will flow. Capital has a robust set of options that allow for the automatic control of how data is changed. Ownership over data is determined in a granular fashion so that the change policy can be tailored to individual design flows. The pieces available for selection are highly detailed, such that rules may be set for specific attributes of individual components. For example, a rule may be set that MCAD is only able to update the weight attribute of a connector, but not the electrical characteristics.
Variant management further complicates change management. Aircraft companies build each of their aircraft to the specifications of the customer. This is particularly true of the plane’s cabin. Different airlines will feature different entertainment options, seating configurations, and so forth. As a result, the wiring harness design of each customer’s fleet is unique. An intelligent, federated management tool and database for the harness design variants is needed. This data manager must intelligently provide mechanical and electrical engineers with up-to-date variant information relevant to their domain without forcing either discipline to adapt to the other’s database.
ON TIME AND ON BUDGET
Technological advancements and new market demands have contributed to the exponential rise in the complexity of aircraft designs over the last decade. ECAD-MCAD automated co-design leads to increased productivity while ensuring a robust design and reducing the cost of quality. Aerospace mechanical and electrical designers are now able to synchronize their data more efficiently and collaborate more effectively on critical design items, thereby ensuring proper implementation of design intent.
During design, seamless cross-probing between the electrical and mechanical environments helps designers understand their counterpart’s domain and provides ongoing cross-domain decision assessment. This enables inconsistencies to be identified and resolved early, reducing costly design iterations. ECAD-MCAD co-design, with rich change management support, provides a key enabler for design teams to reach program milestones, ensuring the project proceeds on schedule, while minimizing cost.
Anthony Nicoli, Aerospace Director
Anthony leads the aerospace business for Mentor’s Integrated Electrical Systems Division (IESD). He is charged with expanding IESD’s contribution to this market. Prior to this role, he led the Mentor Graphics technical sales team serving The Boeing Company. He joined Mentor in 1999, growing to lead the marketing organization for Mentor Graphics’ integrated circuit physical verification product line, Calibre, before joining Mentor’s sales team.
He spent nearly twenty years in the defense industry, developing electro-optic and electro-acoustic systems and businesses, working primarily in the tactical missile countermeasure and underwater imaging domains. He holds Bachelors and Masters Degrees in Electrical Engineering from the Massachusetts Institute of Technology and a Masters in Business Administration from Northeastern University.