Parachute for helos?
I seem to recall a trial for ejection seats for helicopters back in the '70s. The rotorhead was designed with explosive charges on the blade roots to shed the blades in unison at the 3 and 9 o'clock positions This was for a four bladed rotor with blades 1 and 3 being shed and then 2 and 4 as soon as they reached the same point.
Once all the blades were gone and without the pesky rotor disk ready to "CHOPPER" your head off, the Martin Baker ejection seat did its job just like in planks. I would guess that the same system, if it was plausible and viable, could be used... by why bother?
In my VERY humble opinion and being a Chinook driver with a number of parachute jumps under my belt, I'd only bale out of a Chook if I could take a very fast running jump down the cabin and dive off the ramp past the aft rotor...
Otherwise my choice is to take the baby all the way to the ground.
Here's hoping we are never in a situation where we are thinking that a parachute would have been a good idea.
CB