Relationship of RC Brushless Motor Power Output
Why do larger motors produce more power?
In a larger motor you can fit more copper wire and also more or larger magnets. In addition larger motors are able to remove a lot of waste heat. Increasing surface area will help shed waste heat that is produced.
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When brushless motors increase in size, naturally the kv of the motor decreases. As such this allows a motor to accept a higher voltage input thus creating more power. Other specification of the motor such as the Io and the Rm are more relative to the operating current of the motor. These values can be very similar to one another when comparing a larger vs smaller motor.
Here is the relationship between brushless motor weight and power output. Simply multiple a motors weight in grams by the appropriate number and you have a power output approximation.
Inrunners Less than 150 grams Weight X 3 = Power || Greater than 150grams Weight x 4 = Power
Outrunner Less than 150grams Weight x 2.5 = Power || Greater than 150 grams weight x 3.
A brushless car that is in the scale size class of 1/16 may use a 28 mm motor where a 1/10th scale may use a 36mm motor with a length of around 50mm. A 1/8 scales car would use a motor that is 36mm in diameter but a length of over70mm.
For a typical trainer style plane, 75-100 watts of power per pound of airplane would fly the plane very well. 150 watts of power would give significant performance.
A plane weighing 10 pounds would need 750-1000 watts to fly well. Working from the numbers above produces a motor that would weigh approximately 250grams for an inrunner or 333grams for an outrunner.