> Unfortunately the reduced power is still a problem at higher altitudes but for different reasons. Instead of oxygen starvation, the props will have less to pu

> Unfortunately the reduced power is still a problem at higher altitudes but for different reasons. Instead of oxygen starvation, the props will have less to push against. Yes, but air-density-altitute problems are identical no matter what is spinning the prop, righ? > This is still less of an issue as the electric motor can spin faster due to the reduced resistance. Higher speeds will create higher resistances from within the motor itself (which will in turn be increase the heat generated in the motor). OK, so do the math for me here, I am a bit confused. I am not a motor whiz, but torque at the output converted to watts is going to be power at the input less i^2*r losses. The back-EMF will go up as the motor speeds up, so it may be at a somewhat less efficient point on the RPM-versus-torque curve, but the resistance of the actual wires doesn't change. > That heat will also be harder to dissipate in lower pressures, but I suppose alternative cooling could be added as well. I think that is all true. Seems to me you design cooling around the cooling capacity of the air flow at max operating altitude. Is that really a huge design constraint?