Prior to the BO-105, all helicopters utilized what were referred to as semi-rigid rotor systems. In this configuration, the main rotor blades were connected to a central swashplate by articulating hinges that allowed each blade to flap up under power, while also allowing the blades to move fore and aft to accommodate for the lead or lag. As an assembly the system was heavy, and added significant maintenance complexity.
While the original design requirements for the new helicopter were being published, a host of new high-strength, low-weight composite products were beginning to enter the commercial aerospace market. It occurred to MBB that if it could integrate these products within its helicopter, it would be able to generate a significant performance advantage. One of the engineering focus areas was the hefty nature of the hinged rotor assembly and accordingly, it designed and produced a new "hingeless" configuration that was stronger than the original, at a significantly lower weight.
Once the aircraft was fully certified as a hingless system throughout its nominal flight regime, the MBB test community decided to see what else it could do with the aircraft and its new system. Since it was clear that the configuration allowed for significant strength under power, it followed that, since the blades were a part of the fully integrated central hub, the aircraft could actually roll inverted without having the blades fold up. The first time one of MBB's pilots took off to attempt the maneuver, there was probably some concern, but the aircraft's roll performance was acceptable at the end of the day. The only downside was that since the aircraft initially carried asymmetric blades it tended to fall, or "flop," through the roll, rather than producing a well-carved rotation. Once the MBB team mounted symmetric blades, the tendency to flop through was nearly entirely eliminated and the aircraft simply just became more and more aerobatic.
Between the mid-sixties and 1991, when the BO-105 production line was finally closed in favor of a newer light helicopter variant, the aircraft and its rigid-rotor design became one of the most flown and purchased aircraft in history. The helicopter became a favorite among military aerobatic teams along with various commercial airshow teams. Of these, the Red Bull Aerobatic Team is probably best known. Every weekend in the summer, its blue and red helos pirouette across the sky doing seemingly impossible maneuvers.
As a result of the BO-105 and its original design nearly all military helicopters carry rigid-rotor systems today. The innovation has spawned a host of new ancillary systems including; bent-tipped blades for better speed, better all-round flight characteristics, greater lifting capacities and, of course, more complex aerobatics. In fact, the ability to roll inverted in military helicopter operations has engendered entirely new doctrinal thinking throughout the military helicopter community.