Electric PPG - ONE motor project -

I’m not sure the value of arguing about this. Seeking a level of purity in an online community and imposing that as a litmus test seems counterproductive to the general interests. Anyone is welcome to fly and equip any way they want, laws of physics and limitations won’t change.

Ultimately, motor power output is limited by heat. No matter if it’s heat because of eddy currents, hysteresis, bearing drag, or winding losses, the maximum power we can push into that prop is limited by when the motor suffers thermal failure.

There’s a neat aspect to e-flight: the question of whether we can run at high power continuously isn’t really relevant if we don’t have enough battery to run for more than a few minutes. So spec’ing for continuous operation at high power is wasting money, efficiency, and adding mass.

Let me repeat that: if your battery-powered glider is capable of being cooled completely at max power then your design has left something valuable on the table.

That being said, leaving into a design phase anticipating that you will achieve thermal shutdown at the precise moment when batteries reach 20% SoC (or whatever min number you’d like to pick) is foolhardy. So you need some tools in your pocket to be able to help your design over the inevitable thermal hump.

One tool is to overspec the motor. It’s easy and is well-understood with graceful flight failure modes. But it’s not the only way.

The ONE style design offers a potentially interesting way to be more liberal with the motor spec and yet not risk project failure. Water cooling adds significant thermal capacity without adding much mass. Water outperforms copper, alu, and steel by 4-5x. The upshot is that 1kg of water can allow a motor to run at continuous output for 4-5x longer, before even considering the effect of air convection.

Furthermore, the MAD M40 style design offers vapor cooling as a trump card which we can play, knowing that we can solve the problem forever for what amounts to a teensy spray bottle of water. It might not be ideal, but it means we can experiment with smaller lighter motors and that opens the door to cheaper flight with longer fight times and softer landings.

Or are we somehow against lighter, higher performing systems?

2 Likes