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The fan blades in a fanjet are mounted loosely in a fir-tree shaped mount so they are free to lead or lag and balance themselves. The blades on fully articulated and semi-rigid helicopter rotor heads are mounted with a drag hinge that allows them to lead/lag as needed. Do any propeller aircraft have a method to allow the blades to lead/lag, or is this for some reason unnecessary?

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  • $\begingroup$ Are you talking about GA aircraft or something bigger like a turboprop? $\endgroup$ – Ron Beyer May 4 '16 at 2:03
  • $\begingroup$ @RonBeyer Either. Just wondering if this principle is ever used for propellers at all $\endgroup$ – TomMcW May 4 '16 at 2:28
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The two things are completely different and exist for different reasons:

  • Fan and turbine blades are mounted loosely, so they can self-balance. This is because at the very high RPM fans and turbines spin at they are extremely sensitive to imbalance. On the other hand, the self-balancing only works at high RPM. It also requires the blades to be connected at the tips with the “shroud”.
  • Rotors have lead-lag hinges because the rotor spins parallel to the flow so in forward flight the advancing blade meets the air at significantly higher speed than the retreating blade.

Propellers spin slower, so they are not as sensitive to imbalance, and they don't have the shroud, so they can't be mounted loosely anyway. They spin perpendicular to the airflow, so all blades meet the air at similar speed and angle of attack, so they don't need to deal with as big differences in the aerodynamic forces. And they are smaller and more rigid.

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