All rotor brakes that I have come across are essentially similar in design to a car disc brake, with 2 or 4 pistons activating calipers either side of the brake disc. Application is limited to below a specific Nr, most Bells are 38-40%Nr, Sikorsky varies more by type, and so on. Robinson is the only non hydraulic system I've used (pull a chain in the roof of the cockpit which activates the pucks via a cable!), all others are usually via a large overcentre hydraulic piston in the cockpit. S76 has an electrically operated brake in some models: now
that's fierce, no control at all
The disc can be in a variety of locations, from the short shaft between the engine and MGB of the 206, to a specific shaft out of the side of the MGB, or even on the output shaft from the MGB. It depends on the designer, and who knows what influences him......
Bell are quite specific in their operating instructions, requiring the rotor brake to be fully applied until nearly stopped, then eased off to allow a 'soft' stop. Many pilots 'milk' the brake, which is detrimental to it's operation. the 206 wind-up/judder is usually caused by this type of application, and is the tail rotor drive shaft winding up the thompson couplings, not the MGB.
As mentioned, some helicopters (such as the Sea King) have the ability to apply the rotor brake with the engines still running at idle. The SK has an aux drive which bypasses the MGB, and allows blade folding: the rotor brake is one of the interlock requirements to allow folding.
I use the RB nearly all the time. Safer for operations, and also helps to know that it is working: those who leave it until it's really needed can have a nasty surprise waiting when it turns out to need a bleed and fails to work as advertised
