Typically, only the cockpit area is armored. This is the case with the Apache as well as the Hind. I can assume it's the same for the Black Shark, but I don't know that firsthand. Some versions of the Hind (and even Mi-17) can be found with "add on" armor on the sides of the engine and main transmission deck, but this is an exception rather than the rule. The primary protection on a helicopter (once you start getting hit, that is) is system redundancy. This is why you see engines spaced on opposite sides of the aircraft, so that it's less likely to lose both at the same time. In the case of the Apache, not only do you have redundant hydraulic systems (which nearly every medium and larger helicopter has...some even have three hydraulic systems) but the hydraulic lines for each system are routed down different sides of the helicopter, to reduce the possibility of having both damaged at the same time.