Tuesday, October 16, 2018

Blade 180 - Oxy 210 Rotor Characteristics

Product source is ebay seller amain. Item "OXY2-081 OXY Heli Carbon Plastic Main Blade 210mm (Black) (2)"

The airfoil profile is (NASA predecessor)NACA0015. The symmetrical airfoil is generally known to have the center of pressure CP at quarter blade width from the leading edge during cruise flight. As shown in the picture below, the CP point is at 18mm/4 = 4.5mm from the leading edge. The bolting boar of the blade is located at 5mm from the leading edge. That means that the airfoil has perpetual up-pitching torque at cruise attack angle of 6 degrees. The CP is also generally known to shift forward with attack angle. When attack angle is flattened, CP is behind the theoretical quarter split point. 

When the mechanical margin of error is added between actuator servos and actual blade position, the blade angle shifts as the following time line.

This means that large slop gap can result in an unstable craft. And in the above example depiction, the slop should be improved from 3.2 degrees to 3 degrees to escape the perpetual pitch suppression slump. And to avoid over-correction, the slop needs to be smaller than 2.1 degrees.

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