Tobias von Wolffersdorff
Pilot & customer advisor
Landline number: +49 (0)9181 522 99 60
The rotor blades of the first helicopters were connected rigidly to the rotor shaft. This led to an uncontrollable roll movement during forward flight, because due to the higher airspeed the advancing rotor blade generated more lift than the retreating blade. This repeatedly led to problems to the point of crashes. The first one to introduce flapping hinges and rotatable joints was Juan de la Cierva with his autogyros.
Contemporary modern rotor systems can be classified as follows:
- Hinged rotors
- Hingeless rotors
- Bearingless rotors
The hinged rotor systems possess mechanical flapping hinges and rotatable joints, as well as a bearing for the adjustment of the angle of incidence of the rotor blade (Fig 1). These hinges are very heavy on maintenance and thus expensive in upkeep.
In the hingeless rotor system the mechanical flapping hinges and rotatable joints are replaced by appropriately flexible materials at the root of the blade that allow the flapping and rotation movements (Fig 2). This became possible with the invention of plastic. The BO-105 was the first helicopter with such a rotor system.
The bearingless rotor has no mechanical flapping hinges and rotatable joints and the bearing for the adjustment of the angle of incidence is replaces as well with an elastomer bearing. Because no conventional mechanical bearings are used, maintenance can be reduced considerably. Large forces act on the root of the rotor blade and therefore the bearingless rotor with elastomer bearing is only suited for smaller helicopters. This system was introduced by Aerospatial with the Spheriflex rotor.
Also the semi-rigid system can be classified under the hinged rotor systems (Fig 3). This is only used for helicopters with two rotor blades. The blades are connected to the rotor mast via a kind of rocker that allows flapping motions. Rotatable joints are not required for this system.