Lu, this part is fun. Discussing and learning, asking questions, challenging each other. I don't like the stubborness on other threads, but I do like this.
To calculate the centripetal force in the example you gave, we would need to know how the mass in the blade is distributed. It's not uniform otherwise the center of mass would be in the middle not at the 45% point.
If I assume the mass is linearly distributed the centripetal force works out to 8045.4 Newtons or 1808.6 pounds. It most likely isn't linearly distributed, so that answer is only close.
If I just locate all the mass as a point mass at the center of mass, the centripetal force is an easy calculation, mass times radius times angular speed squared. Works out to 2495.6 pounds. It gives you the order of magnitude.
I wrote out the derivation. If anyone wants it, email me.
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You said, "Now, calculate the centripetal forces at the blade attach point but do not calculate the centrifugal forces developed by the spinning blade."
Too late, I already calculated both quantities. Centripetal force is as above, centrifugal force is zero because the blade doesn't develop forces, it is acted upon by a force.
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Now we get into losing one blade.
First of all, remember that bit about "For every action there is an equal and opposite reaction."? The action of the centripetal force is to pull the blade towards the hub. The reaction is to pull the hub towards the blade.
With a balanced rotor head, you don't notice the reaction, because it is cancelled by the reactions of the other blade(s). When the rotor becomes imbalanced, it behaves like there is a force pulling the hub away from where there used to be a blade, rotating 250 times per minute. That motion of the hub is the reaction to the centripetal force that the hub exerts onto the remaining blades.
Does that answer your question?