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Great info Al,
I haven't been able to read through all the posts
because of work lately, so forgive me if this has already been addressed.
The thing that jumps out at me is that the problem
is worse on the 20B. Of course they have more total power, but they also
have 1/3 more cyclic loading due to the extra power pulse per rev. What
matters for machine design and fatigue rating is not only the magnitude but the
number of cycles. A 20B would have roughly the same peak loading, but is 33%
older in fatigue cycle terms than a two rotor. Any TBO issues will show
up first on the 20B installations because of this.
Monty
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