Electric Vertical Takeoff and Landing (eVTOL) aircrafts are revolutionizing how we think about urban transportation, emergency services, and even short-haul trips. Their innovative designs and capabilities promise a future with less traffic congestion, faster response times for medical teams, and more efficient cargo transport. A critical component of these advanced aircraft is their propulsion system, where the motors play a pivotal role.
Let's explore what this means in greater detail.
An Overview of eVTOL
An eVTOL is a type of aircraft that can take off and land vertically, like a helicopter, but with the added benefits of quieter operation, reduced emissions, more efficient lift and cruise, and potentially lower operating costs. There are many different concepts and configurations for eVTOLs, but four primary design architectures (tilt-rotor, lift+cruise, multi-rotor, and vectored fans) are most promising. These aircraft are used for various purposes, including air taxis for short-range urban travel, logistics, delivery, emergency response, sightseeing tours, and personal recreation.
They are a vital element of urban air mobility (UAM), aiming to relieve traffic congestion on city roads. They are powered by electric motors, offering a clean, efficient, high-performance alternative to traditional internal combustion engines. Currently, a significant number of air taxis have been ordered by major airlines to help commuters navigate crowded city skies.
eVTOL Performance and High-Performance Motors
Every gram of mass impacts performance in aircraft. To meet aircraft performance goals, eVTOL companies incorporate the latest in avionics, structural, battery, electrical, and propulsion technologies. Properties such as take-off weight, payload capacity, cruise speed, range, hover time, and flight time are primary measures of performance. Optimization of the motor and electric propulsion unit (EPU) is critical to overall eVTOL performance.
Engineering teams borrowed from the EV industry for initial concepts and prototypes of eVTOL design. These silicon steel-based interior permanent magnet (IPM) motors are economical and reliable. However, with experience, many eVTOL experts now believe the performance limitations of silicon steel IPM motors result in unacceptable tradeoffs in aircraft performance. To meet eVTOL performance goals, they are designing high-power and torque-dense motors based on different topologies and advanced materials.
Iron cobalt alloys are commonly used in APUs and generators for commercial and defense airplanes. They have higher permeability and induction than silicon steels, so they are used for higher power and torque density motors. The comparison below, based on a model of a tilt-rotor eVTOL, shows the aircraft performance improvement from using iron-cobalt.
Higher Torque Motors vs. Smaller Motors in eVTOLs
When it comes to eVTOL design, there's a debate between opting for higher power motors versus smaller motors. The former is renowned for its ability to deliver enhanced performance. A motor with higher power and torque can produce more lift and thrust, which translates to better acceleration and the ability to carry more weight or payload — crucial factors for eVTOL applications.
The performance benefits are similar across multiple eVTOL configurations and designs, as seen below. While specific design restrictions, configurations, and considerations may impact the ultimate choice, optimizing the motor power and torque output is generally advisable for maximum aircraft performance benefit.
The schematic below outlines the two motor optimization paths, the related aircraft design improvements, and the ultimate aircraft performance benefits.
What Are the Aircraft-Level Benefits of Higher Power Motors?
The benefits of employing higher power motors in eVTOL designs are substantial. Take a closer look at these advantages here:
- Range and Flight Speed: Motors with higher power directly contribute to an eVTOL's ability to fly farther and faster. For example, an eVTOL with a more powerful Hiperco 50 motor can see range increases of 12 -20%, depending on the eVTOL design. Enhanced power also leads to improved propulsion efficiency, which means the aircraft can cruise at higher speeds for longer distances, thus expanding its operational envelope, while reducing flight times.
- Efficiency: High-torque motors excel in energy efficiency, which is critical for battery-powered aircraft. Moreover, the reliability of torque-dense motors enhances the safety profile of eVTOLs, which is paramount for their acceptance by regulators and the public.
- Payload Capacity and ROI: The most significant advantage of high-torque motors is the ability to increase payload capacity. A 20% or greater increase in payload — equivalent to an additional 90kg to 135kg —can translate to one more passenger per flight. For eVTOLs with a capacity of 2-5 passengers, this increase is not just a marginal improvement. It's an economic game-changer, maximizing operators' revenue potential and expanding each flight's utility. In fact, it is upwards of up to $1.1 million additional annual potential revenue, assuming the added payload is used for an additional seat on an air taxi or eVTOL.
Carpenter Electrification's Use of Hiperco® 50
At Carpenter Electrification, we utilize our Hiperco® 50, a high-performance iron-cobalt alloy, to create power-dense stator and rotor stacks integral to high-torque eVTOL motors. This alloy is renowned for its excellent magnetic properties, allowing for compact, power-dense motor designs that push the boundaries of what's possible in eVTOL propulsion.
These stator and rotor stacks made from Hiperco® 50 allow us to build motors with up to 25% more torque density, 30% more power density, and a reduced size of up to 30%. As noted, a higher power, higher torque motor has the greatest impact on improving eVTOL performance, most notably with payload capacity, but also range. Additionally, our use of Hiperco® 50 leads to cooler operating temperatures, extending the motor's lifespan and enhancing reliability.
Final Thoughts on eVTOL Innovation
The future of aviation is electric, and higher torque eVTOL motors are at the forefront of this transformative era. Carpenter Electrification is dedicated to advancing eVTOL technology with our Hiperco® alloys and stator and rotor stacks, contributing to a future where air mobility is more accessible, sustainable, and efficient. With the ability to improve aircraft performance on multiple fronts, from payload capacity to flight range, higher torque motors are set to become a cornerstone of modern aviation technology. If you want to learn more, our team is here to help address your motor design needs for current and future eVTOLs.