On Apr 8, 8:56*am, JJ Sinclair wrote:
My Nimbus 3 came down from a wave
flight with hundreds of cord-wise cracks and I deliberately came down
slow and avoided the rotor.

JJ -- OT, but the damage happens on the up.

It's the downward transient in temperature that creates tension in the
surface layer and leads to cracks. True in turbine engines and just
about any other engineering structure subject to thermal shock. Think
of it this way: the surface gets cold first, shrinks first. It's
restrained by underlying structure, result is tension on surface,
compression in substrate. Reverse happens on warming.

-Evan Ludeman / T8