How “Follow-The-Wire” Methodology Can Optimize eVTOL Connectivity

What you’ll learn:

• What is the “follow-the-wire” (FTW) approach?
• How FTW addresses the increasingly complex requirements of electrically powered aircraft.
• How engineers can use the FTW approach to optimize eVTOL connectivity solutions.

The growing demand for commercial drones and electric vertical takeoff and landing (eVTOL) aircraft is driving advances in electric-propulsion motors, power distribution, positioning systems, telenetworking, and cockpit/mission systems. These opportunities continue to inspire engineers to explore components that can optimize size, weight, and power (SWaP) for line replaceable units (LRUs) in advanced air mobility (AAM) innovations.  

Recently, a design optimization technique, known as “follow-the-wire” (FTW), has emerged as a valuable approach for designing solutions that handle applications involving high voltages and high-power peak outputs.

To better understand how FTW can be used to optimize connectivity in drones, eVTOLs, and other electrified aircraft, Lee Goldberg, Electronic Design’s Power Management Editor, sat down with Matt McAlonis, TE Connectivity’s Director of Advanced Systems & Architecture and Engineering Fellow for aerospace, defense, and marine systems. The wide-ranging discussion provides some helpful insights on how engineers can use FTW to optimize the low-voltage, high-bandwidth connectivity and control interconnect solutions typically found in mission systems and in-flight entertainment (IFE). 

ED: What are the technologies, technical standards, and products that need to be more fully evolved to enable eVTOL aircraft, as well as to give them the payload capacity, range, and cost to compete with conventionally powered vehicles in a broader range of applications?  

McAlonis: The primary driver for enabling eVTOL aircraft for AAM are the propulsion systems. Traditional commercial aircraft systems typically operate under 300 V, while new electric aircraft will operate at nearly 1,000 V. This higher voltage creates significant challenges across multiple applications. 

Increased power is achieved through voltage levels which require thicker insulation and dielectric materials to withstand the higher voltage. Additionally, higher amperage levels lead to power distribution and thermal management, and increased weight challenges, pushing the limits of traditional connector ratings and leading to potential overheating and accelerated material failures.  

Another difference between eVTOL and traditional commercial aircraft is altitude. While a typical airliner cruises around 40,000 feet, eVTOL aircraft don’t have pressurized cabins and operate at much lower altitudes, up to 15,000 feet above sea level, more in line with those of a helicopter. Voltage ratings are directly correlated to altitude usage as the air density changes. 

Without the need for thick cabling and shielding to protect from the partial discharge challenges in high-altitude conditions with thinner air, eVTOL aircraft can benefit from lighter, smaller components to support weight-sensitive applications.  

Because electric aircraft will be charged on the ground and won’t lose weight as they burn fuel in flight, there’s another opportunity to optimize conductor materials for weight reduction and shape. TE Connectivity is working on shape-optimized power cables that can handle 30% to 40% more power for an equivalent conductor cross section versus traditional cables. This means lighter cables can fit into tighter spaces, which optimizes aircraft design and range. 

Power-distribution units are also critical for simultaneously managing different systems that don’t run at the same voltage, like radar systems, flight control, and air conditioning. TE Connectivity makes solid-state relays (SSRs) with higher reliability, smaller size, lighter weight, and higher performance than traditional electromagnetic applications. The latest relay technology can monitor power levels and send alerts when there are slight variances outside the nominal range that could develop into more significant problems down the line, thus helping prevent incidents before they take place. 

SAE has established an Electrified Propulsion working group called E-40, where AE-8 covers Electrical Wiring (EWIS) standards, AE-7 is the Electrical Power & Equipment group, and AE-7D is the Energy Storage and charging committee. 

What advances are you seeing from the hundreds of commercial drones and electric vertical takeoff and landing (eVTOL) aircraft programs? 

It’s important that eVTOL programs develop test rigs that accurately simulate the motor motion in application so we can measure cable flex endurance before mechanical failure. Because many eVTOL aircraft require power cables that flex continuously as motors articulate during flight, it’s critical to know how frequently they need servicing.

For example, when you flex a cable that many times, how long will it last until the braid that shields the cable starts to fail or the conductors themselves start to break from mechanical fatigue? That becomes a service item on an aircraft that, in previous aerospace applications, used to be installed and left alone until proven faulty. 

There have been significant advancements in the testing methodologies to assess engine and motor performance without the risk of crashes by creating eVTOL-specific test sites. This is helping eVTOL providers prioritize safety while ensuring the engine and motor systems are ready to enter the market. 

We’re also beginning to see chromatic indicator materials, such as a cable that could change color when it gets too hot. This can help eVTOL maintenance providers quickly inspect and swap hardware as needed. Combined with the SSR predictive maintenance I mentioned before, we’re seeing a new wave of redundancy and safety technology beginning to advance. 

What is the impact of these advances? 

Increased testing with decreased risk makes eVTOL aircraft advancement more accessible and, therefore, more accelerated. Without the risk of injury or loss of investment, engineers will be able to significantly enhance the safety, reliability, and maintenance of electric aircraft at a quicker pace. 

What are some of the challenges you’re noticing that engineers face when trying to optimize eVTOL aircraft connectivity?  

Reliability, redundancy, and integration are critical challenges when optimizing eVTOL aircraft connectivity. As we know, eVTOL aircraft require flexible, high-durability cables that can endure the thousands of motor articulations in flight, so reliability is a key concern.  

On top of that, it’s crucial to ensure system redundancy and fail-safe mechanisms for connectivity failures while we develop the solutions to meet these new demands. 

System integration is also a key challenge for optimizing eVTOL aircraft connectivity. Standardization can be particularly difficult because each connection point needs to accommodate different voltage, thermal, and mechanical requirements. 

What is follow the wire and how can it be used to help address those challenges? Are there any roadblocks to implementing the FTW approach? 

The follow-the-wire approach is a method for mapping electrical connectivity throughout an aircraft that allows engineers to identify weak links, optimize compatibility, and enhance maintainability. Our advanced systems and architecture team walks our customers through a schematic to identify the nodes of connectivity that need to be considered.

FTW pinpoints bottlenecks in power distribution, flexibility, or reliability by tracing power and signal paths. It also ensures all subsystems are backed by compatible products with the correct voltage and temperature ratings. By ensuring all components are correctly matched for performance, FTW aims to reduce potential failure points. It also enables troubleshooting and maintenance through standardizing wire and connector selection. 

A major roadblock to implementing the FTW approach is that it requires a high level of trust and transparency across the supply chain among people who understand the products and people who have a vision of what the system is meant to achieve. It takes time, but the benefits are immense, so it can be an important part of long-term supplier-customer relationships.  

Geographical standards have become another roadblock to the FTW approach, because different regions have different regulatory requirements, so eVTOL providers must be aware of different product differentiators in each of the downstream systems. An experienced supplier can help customers navigate regulatory pitfalls that could otherwise cost significant time and money down the line.  

Where would FTW have the greatest impact (and what components are driving that impact) on advanced air mobility? 

There are many areas where FTW is important for AAM applications. I’ll share a few examples of the conversations our team has had with real customers.  

First is power distribution. Rather than our customers purchasing all of the individual products that comprise an eVTOL power-distribution unit (PDU), we can provide PDUs tailored to customers’ needs. With the FTW approach, we can provide another level of customer service so that our customers don’t have to buy hundreds of individual parts. Instead, we can build the PDU for them. 

The next area is avionics, flight control, and navigation. Reliability is crucial for connectors in the circuit boards that control collision-avoidance software, communication systems, weather radar, and flight trajectories. Our FTW approach ensures we’re doing due diligence in understanding product needs and providing the highest reliability. 

The FTW process has also helped us develop dual-purpose structures, such as those that integrate lightning protection and cable management into composite airframes. In eVTOL aircraft, customers are always eager for opportunities to combine functions and save space and weight.   

Finally, while infotainment and cabin interior power are more of a “nice to have” compared to mission-critical systems, we can use FTW to enable weight-optimized power solutions for passenger experience systems like Wi-Fi, seat power, and displays while maintaining cost-effectiveness. Because these systems are non-critical, they ensure redundancy without unnecessary weight or complexity. 

How does the FTW approach differ from other technical approaches? What are the pros and cons? 

The FTW approach helps us better understand the problems our customers are trying to solve and highlight any weak links in a system. Also, when we work closely with our customers, we can offer other solutions to increase efficiency and shorten time-to-market. 

An alternative approach is for a customer to continue the traditional sourcing of individual components with a risk of incompatibility between products and brands. There may be many alternative approaches to the design solution, but due diligence to ensure materials and processing compatibility and design integrity must be validated.