Musk isn't correct though, or maybe you misunderstood or misquoted him. Higher speed is only more efficient if the craft itself moves at a higher speed.
To explain a bit further: a prop is at its most efficient when it has clean air to work with and that only works if the craft moves forward at least as much as one prop's worth of air in the direction of motion. Less than that and the prop will encounter it's own backwash. This is the reason why variable props exist, to ensure that the prop has enough 'bite' rather than that it just churns the local air. So at low revs you run a higher angle than when you go faster and towards the tips of the prop the angle gets flatter as well.
Which more or less defines the range of a variable prop, once the tips are nearly flat there is nothing more to gain. Another important factor is blade count. A single blade is theoretically most efficient because it can run at the highest RPM before the blade encounters it's own wake again, but there are balancing issues and vibration issues with low (<3) blade count props. And in practice the efficiency gains are offset by complexity, weight (a single blade needs a counterweight) and drag of that weight. Two is common enough though because it is easy to make a sturdy two blader prop. Three is optimal from a longevity and maintenance point of view, and a offers very good efficiency.
And I think you meant 'electric', not 'electronic'.
> Musk isn't correct though, or maybe you misunderstood or misquoted him. Higher speed is only more efficient if the craft itself moves at a higher speed.
He's got it completely backwards from what Musk said in that interview, see my reply.
Hm, I don't entirely know how this works, but for RC planes we use slower motors and higher prop pitch for efficiency, faster motors and lower prop pitch for acceleration.
To explain a bit further: a prop is at its most efficient when it has clean air to work with and that only works if the craft moves forward at least as much as one prop's worth of air in the direction of motion. Less than that and the prop will encounter it's own backwash. This is the reason why variable props exist, to ensure that the prop has enough 'bite' rather than that it just churns the local air. So at low revs you run a higher angle than when you go faster and towards the tips of the prop the angle gets flatter as well.
Which more or less defines the range of a variable prop, once the tips are nearly flat there is nothing more to gain. Another important factor is blade count. A single blade is theoretically most efficient because it can run at the highest RPM before the blade encounters it's own wake again, but there are balancing issues and vibration issues with low (<3) blade count props. And in practice the efficiency gains are offset by complexity, weight (a single blade needs a counterweight) and drag of that weight. Two is common enough though because it is easy to make a sturdy two blader prop. Three is optimal from a longevity and maintenance point of view, and a offers very good efficiency.
And I think you meant 'electric', not 'electronic'.