[audunw]

> Given that the batteries weigh a lot more than the motors, I would have thought that motor efficiency (which scales battery size) was much more important than motor weight.

I guess that depends on what kind of airplane you are making. If you're just making the same kind of airplanes we've been making with ICE, but with electric motors and batteries instead, you're probably right.

But if you're making an electric airplane from scratch, there's a lot you can do if you have a really light motor, which can drastically reduce drag.

Look at Maxwell X-57 for instance: https://www.youtube.com/watch?v=-HvZ7c0F9ik

If you're going to have lots of motors on the wings, they better be as light as possible.

I'm guessing the increased efficiency from a design like that can easily be as important as the efficiency of the motor itself.

[mliben]

These are all great points- everything is very interconnected in these vehicles, and there is a lot of potential upside in high power density distributed propulsion (like on the Maxwell).

In characterizing the vehicle-level benefit of power density, it is definitely important to consider the X kg of structure required to support 1 kg of motor/inverter/gearbox/etc.

[toss1]

Excellent points about associated structures! However for the motors, isn't it the case that the support structure design is dominated by the thrust loads, which should vastly exceed the motor mass? For sure, there is some non-thrust-related structure to react the motor's mass, e.g., inertia from a harsh landing, but how much extra is it? This is much more the case with power/mass optimized motors like yours.

Consider an ideal case - you achieve the same power with negligible mass, say 1kg. How much structure in my aircraft using your motor could I really eliminate vs your current model?

And the real case, switching from a competitor's similar-power motor to yours, how much additional structure weight can I save by switching, beyond the obvious great advantage of your motor's weight savings?

(Obviously, these answers massively depend on other factors, but... )

[mliben]

Yeah, there are a lot of factors that play into this. A couple things come to mind:

1) Considering megawatt-class machines are necessary for many future applications, the mass of the motor+inverter+gearbox (especially using best current technology) definitely adds up.

2) With a very distributed propulsion system, motors that end up near the wing tips have a big moment arm compared to the ones typically tucked under the wing root

[toss1]

Excellent point about the moment arm and control issues! I'm definitely all about maximizing power-weight and strength-weight ratios...

I am wondering about the ratios you are achieving, and about the issues of scale.

Do things get better as you scale up? I notice you mentioning the state-of-the-art at 3-4 kW/kg, and you shooting for 12 kW/kg.

This is even substantially better than small scal T-motor UAV motors at around 7w/g [1]. The chart shows them peaking at 3181W and weighing 453g.

So, I'm wondering what scale factors may be working in your favor at your scale vs the single-digit kW scale.

Also, any plans to scale slightly smaller (I'm involved in such a project)?

[1] https://uav-en.tmotor.com/html/2021/Antigravity_0119/668.htm...

[mliben]

From an active mass (electromagnetic parts, power switches, etc) perspective, our specific power is relatively consistent from 100 kW up to 1 MW. TBD on lower or higher than that.

The biggest difference is the total mass specific power (including housing, bearings, etc) usually gets worse at much lower powers (1s-10s kW), because these components become a more significant fraction of the total mass.

The 12 kW/kg number is continuous output power / total system mass (active + inactive, including motor, inverter, gearbox, housing, bearings, etc). If you isolate just the motor to compare, it is much higher than 12 :)

We do have plans to develop a ~100 kW (maybe a bit smaller) unit in the future, but when is TBD.