ORIGINAL: doxilia
As far as efficiency goes, that is exactly the issue we've been talking about above. Taking a low KV motor, under driving it with a little prop and cranking it up with lots of potential difference puts the efficiency at the verge of the precipice. Naturally the converse is true too. Glow wise it's like taking a Hanno and putting a pylon prop on it or, conversely, taking a VF and loading it with a 14x10. That seems a little more laughable but on YouTube you will see exactly that.
I've got to disagree on this point. Assuming identical stators, the low KV motor is designed to run at a higher voltage to turn the same rpm as a high kv motor does at a lower voltage. The main difference is that at twice the voltage you only need half the current. It's an electrical juggling act nothing more nothing less. The lower kv motor will generate the same torque at half the current because it has twice the number of turns. I'm not underpropping the 400kv motor then running higher voltages to get the rpm, it's designed to run like that.
With only 1400watts to spend, it's clear that for competition work you can have large thrust at low speed or small thrust at high speed and each airframe and flying style requires the competititor to find a happy balance between the two. Of course the bigger diameter prop at lower RPM allows you to spend those 1400 watts more efficiently.
ORIGINAL: doxilia
Brett,
your description of what I mean by ''elastic'' is right on. I like to associate motor ''KV'' with engine ''stroke''. Short stroke = high KV, long stroke = low KV. Likewise, nitro percentage can be associated with electric potential (i.e., voltage). Fuel consumption with current and so on...
David
On paper (and in the scorpion calc application) there's negligable difference between the power curve between a 800kv motor running 5s and a 400kv motor running 10S assuming its a pure winding change. They both pull (and put out) the same power with the same loads at the same rpms, so on paper the elasticity argument doesn't appear to be supported. HOWEVER, in flight perception might be a factor here. The longstroke/shortstroke analogy really doesn't apply, again it's just an electrical juggling act.
I agree, we'll never get the two-stroke effect of the power building as the load drops off out of an electric motor as the power curve just doesn't work that way but I can live with that, although it would be very easy for an ESC manufacturer to make that happen. The ESC only needs to know the RPM, motor current and throttle position (hey they already know that!!) and pull the output pwm duty cycle from a user generated 3d power map (or extrapolate from a simple 2D one).