What would it take to build helicopter blades that can fold in several parts?
This is the continuation of a question on Aviation. Unfortunately, there have been no use case for this for existing helicopters, so no-one has spent millions trying to work out if it was possible, let alone how to do it. As far as real life is concerned, folding helicopter blades at the rotor hub is good enough. As such, the question seem impossible to answer on a more reality-grounded place like Aviation, hence why it is continued here.
Assume that I have developed a magical helipack, or some other sort of ultracompact helicopter with a magical black-box power source. The helicopter itself is either contra-rotating or tip-jet to avoid the need of a tail rotor.
The problem is that while the helicopter itself is extremely compact, there is this enormous rotor and its long, long blades that get in the way when not flying.
Folding them at the rotor hub, as is done with conventional helicopters, helps a bit. However, blades of several metres long don't fit into the nice little backpack like everything else. For that, I need rotor blades that fold in several parts as well.
How would a rotor blade that can fold in several parts be designed? How good would it be as rotor blades? How much more would it mass?
Less-than-ideal blade efficiency is an acceptable tradeoff, as is (obviously) increased complexity. As the outer edge contributes more than the center, it is also acceptable to have the blade not generate lift from the inner parts, as long as the loss of efficiency is not too severe. However, the thing must be reasonably safe, so we want to avoid it falling apart as soon as one pin breaks.
If the design would be different for a conventional (contra-rotating) system or a tip-jet, please point out the differences (or their absence).
Bonus points if the blade can unfold by spinning it or in some other automatic way, so the user can press a button, deploy the rotor and have it open by spinning - allowing them to instantly fly off while screaming "I'll get you next time" at the heroes who just foiled their plans. Having to stop and unfold them by hand would simply not be as theatrical.
Extra-bonus points if it can also fold back automatically after stopping it. Again, not having it to fold it yourself right after landing, wasting no time to Save the Day, just looks better.