I don't agree with the mindset of using an electric motor to synthesize a glow motor. It'll never work as well as if you use the most efficient setup you can physically fit in the aircraft.

I see this all the time, and I used to go along with it, "hey there sonny, what you got in that thar plane?"
A something something something"
"What's that equivalent to?"
I used to tell them a glow capacity, but I soon realised that a) it's misleading and b) annoying. Now I reply in watts.

Some get it, some look at me like I'm retarded. That could be because I drool a lot and stare at them crazy-eyed.

Bryan,

That phenomenon is due to the fact that many of us are stuck with 500 year old power concepts first attributed to yak's and later, when we became very hip..., horses.

Tell them to check out their car manual and look for the engine power. I bet it will be in kW! Otherwise, tell them to change a light bulb - same concept.

Question is, do they know their glow power in horses...?

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.

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

Yep, I think your assessment is right on.

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.

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).

Yes that conquest is a much larger airplane. I remember the first time I saw one in person at a contest. I was still flying a tipo, and I was struck by the sheer area of those stabs!

Maybe I'm old school, but I like the E-flite motor naming conventions. Power 25, Power 46, Power 60. They make sense to a glow flier.

The may make sense, but the numbers are pretty arbitrary in my opinion. I've flown models with 46 outrunners in them that go like smacked cats. When they're set up correctly there's more power there than a 46. Same goes for the power 10. More like a 25!