I need answers

It's an instinct, even though perfectly safe I crouched getting in and out of helicopters. Also, the turbulence created by the spinning blades makes you want to duck for the same reason as why you automatically go in that typical half-crouch in a heavy storm.

That would be a lot of momentum to burn off in a short period of time. I would imagine it would jolt the helicopter a great deal trying to stop that thing in a handful of seconds.

I used to work around some 204's and 206's, when I worked seismic. It takes a while for the jet engine to power up and get to speed, and same with the blades. The blades, if I remember right, only turn at over 400rpm. Also the length and size of the blades will be a factor.

Not worth the effort. Engines have to have sufficient heat and momentum. You don't want any kind of clutch that could break and cause lack of lift when you need it, and the engine (usually jet engines) need the load to keep from over reving. Actually, you see people bending over to walk under the blades and 99% of the time it is not necessary. Take a look at a Huey for example. The rotor head is about 12 feet off the ground. Unless the pilot is stupid or careless, they will keep the rotor disk parallel to the ground, which means the tips are 12 feet off the ground as well. I may be tall (6'2") but that still leaves almost another 6' from my head to the rotors. I believe the Blackhawks the army uses now has rotors that are even higher off the ground.

The CH-46's I crewed on in the USMC have two rotors running counter to each other. I have been witness to a blade strike on an LPH ship while under way- heavy seas caused the deck to pitch, the blades flexed down and literally scraped the deck. THAT was a pants-crapper! If they lost a blade, it'd take out the other rotor head and 6 blades disintegrating at speed means a pretty good zone of destruction. Nothing happened that time, other than emergency shut down and blade inspection, but.... Granted, not many people are on ships with helos, but being 5'5", I still crouch when I'm under spinning blades!

I agree that on shipboard, I would be much more likely to crouch! Since I never had to deal with a heaving deck, that was not in my mind.