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Posted by rev.iain | Apr 21, 2013 @ 08:19 PM | 9,352 Views
Here is some basic information about choosing electric power systems for model aircraft.

This applies to inrunner and outrunner motors unless otherwise stated.

First, a little history:

The inrunner brushless motor first came into prominence in the late 1990s. They were expensive, powerful, of relatively high Kv and so usually needed a gearbox to work for a model airplane application.
For model helicopters, with built in reduction gear systems, they were ideal.

The cost aspect was the biggest obstacle to general acceptance of the new style of motor.
Manufacturers began to think outside the box, and Hacker in Germany created some of the first outrunner brushless motors in the early 2000s.

Many others copied the design, and the brushless outrunner became the sport flier’s choice for electric powered aircraft.
The outrunner style of motor, even in the smaller diameters, makes it possible to get more magnetic poles in the rotor (or "can") and more turns on the stator, and so reduce the Kv of the motor.
By reducing the Kv it became possible to turn a larger prop and so produce large amounts of thrust (torque).

What is Kv?.
The Kv is the voltage (K)constant of the motor. That is, the revolutions per volt in an ideal system, that includes perfect motor, ( 0 resistance ) and 0 pitch propeller with no weight.
The value is used for comparison purposes, rather than an absolute performance figure. For instance; for the average sport flier aircraft a Kv of 1000 is...Continue Reading