It wasn't flipping that fast when it exploded. it was on its final flip where it was about to come to a rest when it exploded and I did not have any weapons loaded.
I've done this at various speeds, slow speeds generated the same result.
There's a video on youtube of a UH-60 clipping its blades on the side of a mountain then "gently" rolling down the side of the mountain. http://www.youtube.com/watch?v=qO1F6iqsUUE
I did this with the KA50 but it exploded, I retried multiple times with various mountains and slopes but it always explodes.