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main rotor spindle of helicopter


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I want to know what forces are in helicopter main rotor spindle?

for example bending or tension

and where this forces act on spindle?

the picture of spindle is in attachment



The rotor head including the spindle are subject to some peculiar forces and moments. You have the basic cyclical forces of lead-lag, flapping, and feathering along with the standard forces of lift and drag. However, the most dominant force affecting the entire rotor system is centrifugal force. The average light helicopter experiences 6 – 12 tons of centrifugal force trying to pull the spindle and blades free from the axis of rotation. Larger helicopters may develop up to 40 tons of centrifugal load on each blade root. That's a lot of tensional stress.


The term centrifugal force is most commonly used. However, centripetal force (action pulling toward the center) is the actual force. Centrifugal force is the apparent reaction.

Edited by iChris
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Take the 300C as an example with a rotor radius of 13.41 ft. turning at 470 RPM and an assume blade weight of 20 lbs. When you plug-in the numbers and do the calculation, each of the three spindle/grip assemblies hold a tensional stress of 10,000 lbs (5 tons) each.


Because of the high stresses visual inspections for cracks and wear are regularly required for all rotor heads.


Inspection Example


Note in the calculation that the radius and velocity should be at the center of mass. The center of mass was assumed to be the mid point (6.7 ft) for radius and velocity calculation.



Edited by iChris
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