Some general notes about the use of our MaxNEO Brushless motors to power "Ducted Fan" model aircraft. Since this is not our area of expertise, we welcome specific data, and photos that we can share with our other customers.
This is one of the better applications of brushless technology. It is especially favorable when compared with the use of brush DC motors. The brush service requirements of a ducted fan DC motor will, of course, be eliminated. Since brushless motors provide a more efficient conversion of electrical power into mechanical thrust (via the rotation of the prop or fan), you can expect longer flight times or more thrust with an equal number of cells. In most cases a brushless power system will weigh less also, allowing an additional cell or 2 to be used, increasing the performance further.
We ran some basic tests back in 1994 with a Kress RK-709E Fan Assembly. This fan on 12 or 14 cells would turn about 22-25,000 rpm and require about 50 Amps. This produced sufficient thrust to raise the fan, motor, and battery pack vertically off the bench. Not very scientific, but a good indicator of future potential.
We have a west coast customer who is using our older Max15-13D motor with a gear ratio of about 1.6:1 to drive a Violett 4.75" diameter fan on 10 to 16 cells. This provides plenty of thrust to power a 50" ws. Heinkel like model for quite lively flights of about 5 to 6 minutes duration.
We strongly recommend the use of gearing to move the operating point of the motor (and controller) to a more power efficient current level. The point is, you can turn that larger fan at a reasonable rpm and current by adding a couple more cells, get the thrust you're looking for and be more satisfied with the flight time.
Analysis of motor performance curves for a case where a fan speed of 20,000 rpm is desired indicate the benifit of gearing. With a direct drive on 12 cells, it would require about 60 Amps. With a gear ratio of 1.63:1 (MaxGR or Astro-Flight gearbox) it would require only about 27 Amps. This might suggest that we could increase the cell count to 14 and still have reasonable currents for high performance.
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