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Alan,
I am puzzled by your comment "Two separate power source's for the Shack Contra Prop"
You would do well to be puzzled, had I written that. To save you scrolling back I wrote:
In simple installations such as the Griffons in the Shackleton I'm not sure how much account is taken of that, but when the two props have separate power sources various schemes have been used.
If that is not clear enough I cannot and will not help it, but it seemed clear enough when I wrote it that I was contrasting the Griffon/Shackleton props with those driven by separate power sources (e.g. Macchi MC72, Fairey Gannet, Brabazon and SARO Princess, etc.).