Here's the very short version of this page: Electric aircraft have more range than many realize—enough to be viable for business. To unlock their full potential, power density must increase significantly. By maximizing the motor's radius to the size of the fan's circumference and eliminating gearboxes, we can optimize both specific and volumetric power density. Although moving the motor to the circumference presents a challenging bearing issue, 8Phase plans to solve this by magnetically levitating the rotor with the same coils that drive its rotation, removing the need for traditional bearings. Continue reading for the long version...

Not bad...

The above range estimates are based on conservative assumptions for "normal" airplanes. No special blended wing body, blown wing, distributed propulsion, unconventional aspect ratios, or other fantastical advancements are required—just a regular, tried-and-true airliner with batteries instead of fuel tanks.

What about battery stress and degradation? A large battery mass fraction effectively mitigates many concerns. During flight, discharge rates would range between 0.5C and 1C, which is relatively low. If the standard 45-minute aircraft turnaround time is used for charging, the batteries would be charged at a gentle rate, under 0.7C. This approach allows the battery chemistry to be fully optimized for energy density without the need to prioritize power density. Additionally, these low C-rates make it easier to manage battery temperature. Consequently, the batteries are expected to experience only about 10% degradation even after 50,000 flights, with each flight considered a partial cycle.

In a future update, we'll dive into the math behind the fuel cost savings, but for now, imagine the cost of powering your flight being closer to that of in-flight peanuts than today’s jet fuel prices. Wendover Productions made an amazing video on the topic. 

As long as jet fuel remains costly, battery charging stays cheap, and the market remains competitive, it's only a matter of time before most short-haul flights transition to electric aircraft. However, before we can roll out a 150-passenger all-electric 737, we face the challenge of developing a super-powerful electric motor and an innovative wing-shaped battery. And of course, there's the small matter of getting the FAA to sign off on safety—just kidding!

In reality, the FAA will require overwhelming proof that these new motors and batteries are incredibly safe. This proof won't just come from bench tests, ground tests, or even flight tests, but likely from the operation of large electric drones commercially. These drones, which can perform missions without risking human life—and in some cases, even reduce such risks—face fewer regulatory hurdles. If and when these large electric drone businesses succeed, leveraging technology designed for future airliners, we'll accumulate millions of flight hours. Assuming sound engineering practices, this data could provide the necessary evidence for type certification of electric passenger airliners.

However, there's a technical challenge to this approach. No drone will use a motor with specifications anywhere near what an airliner requires. Take a look at these graphs.

When designing larger aircraft, a good rule of thumb is that for every doubling in the aircraft's length, the power output from the motors needs to increase by about 10 times. This may sound surprising, but it makes sense when you break it down.

First, when you double the length of a three-dimensional object, its volume (and therefore its weight) increases by 8 times because volume is proportional to the cube of the length (2³ = 8). However, the wing area only increases by 4 times (2² = 4), which means the wings need to work harder to lift the much heavier aircraft, leading to higher takeoff speeds.

Additionally, while the plane's length and weight have increased significantly, the distance between the wings and the ground (which affects propeller size and efficiency) only doubles. This means that although the propeller disc area increases by 4 times (2² = 4), it still needs to handle 10 times the power to effectively lift and propel the larger aircraft.

To take the largest electric drones flying today and scale them up to 737 sized, the power per unit of disc area needs to increase by more than 200 times.

Here is where 8Phase is taking a different approach than almost everyone else. To achieve high power density, everyone is driven by basic physics to optimize the two main components of motor power: RPM and torque. While it's essential to be a master in blade design and to maximize the current flowing through the copper windings, let's focus on RPM and torque, assuming our competitors are equally adept in power electronics and aerodynamic design. Simply put, more torque or higher RPM translates to more available power.

• Torque is the product of force and distance.

  1. Force: The magnetic force in a motor is closely tied to the mass of copper in the windings, which is generally proportional to the motor's weight. Optimizing the wire gauge ensures maximum current flow, especially when back EMF is highest. However, it's fundamentally the mass of copper that determines the maximum possible electromagnetic force.

  2. Distance: To increase torque, you can enlarge the motor's radius, maximizing the lever arm—the distance between the axle and the coil where magnetic forces act.

• RPM: The speed at which the motor's components rotate is crucial. However, the physical limits of our environment impose constraints. On Earth, with our nitrogen-rich atmosphere and mild temperatures, the tips of propellers and fan blades can't exceed about 760 mph without encountering issues as they approach supersonic speeds. This means you can either spin a large-radius blade at a slow RPM or a smaller-radius blade at a faster RPM, ensuring the tip speed remains subsonic.

This leads to two key choices...

Most electric aircraft companies have opted for pancake-shaped direct drive motors, maximizing torque without the added complexity of a reduction gear set. Gearboxes, while useful, come with their own set of challenges—they're expensive, heavy, and introduce additional failure points. However, gearboxes do allow the motor to spin at much higher RPMs without worrying about tip speeds, enabling more power extraction.

Direct drive motors in aircraft could be designed to spin faster and output more power for the same weight, but they are constrained by the transonic blade tip speed limit. As a result, these motors inevitably leave a significant amount of performance untapped.

When scaling up to something the size of a 737, it’s tough to say which approach will ultimately prove more effective. However, imagine a direct drive motor with a radius as large as the propeller itself—this design would be a game-changer. That’s where 8Phase and the rim-driven motor come into play.

8Phase is reviving an old marine motor architecture that tackled a similar challenge in the world of boats. By moving the motor from the hub to the circumference and fully committing to a ducted fan design, you can theoretically achieve the maximum performance possible from a direct drive motor.

So, should we also move the bearings to the circumference? Unfortunately, that introduces new problems. At near transonic speeds—like those experienced by the blade tips—most materials would deform, and all materials would heat up significantly. Plus, power losses in a bearing are greatest when it has a large radius.

What about placing the bearing at the hub? This approach seems more likely but would require the rotor and stator to be impracticably stiff to maintain a consistent air gap between the magnets and coils, especially in an axial flux motor. Even with a radial flux design, the air gap would change dramatically at high speeds as the rotor deforms under centrifugal force. In either case, any asymmetric deformation would rapidly accelerate bearing wear.

The more you dive into the challenges of bearings, the more it seems impractical to make a rim-driven motor for high power aviation. But what if you could eliminate the bearings entirely? Enter 8Phase again... and also NASA...

NASA had a similar idea two decades ago and even developed a working proof of concept. Their paper, 'Development of a 32 Inch Diameter Levitated Ducted Fan Conceptual Design,' explains the project's motivation better than we've done here. NASA's approach differed from 8Phase's in several key ways. In their design, a starter motor spins the fan up to a minimum speed, at which point passive stator coils generate a repelling force, passively stabilizing at least two degrees of freedom (possibly more, though the exact number isn't clear).

8Phase, on the other hand, has taken a completely different approach, avoiding a starter motor and passive components altogether. The 8Phase design uses a series of laser position sensors to continuously monitor the rotor's position in free space and the alignment of the stator coils with the rotor pole pairs. All six degrees of freedom—linear and rotational movements along and around the X, Y, and Z axes—are actively controlled by an integrated motor controller driving eight independent coil groups. This creates a system that relies entirely on high-speed control to correct the rotor's position and angles thousands of times per second.

Okay, cool—we’ve got a motor that levitates on a bed of lasers, which is pretty nifty. But didn’t we say we need to start with drones to have a shot at certification, and didn’t we mention that drone motors wouldn’t even be in the same class? Yes, we did. But there’s one exception: larger, high-speed drones will require similarly power-dense motors. Essentially, anywhere you see turbojets or turbofans being used today, that’s where an 8Phase motor could drop in as an electric alternative. Obvious use cases include military target drones and cruise missiles. There’s also potential for frictionless reaction control wheels on spacecraft.

Electric planes have more range than you may expect—enough to be business-ready. To push the limits, we need motors with extreme power density. 8Phase is tackling this by maximizing motor radius and levitating the rotor, eliminating gears and bearings to simplify the design. It’s a bold step forward, starting with drones and potentially reshaping the future of aviation.