Helicopter main rotor

Fig. 2.2. Aerodynamic sources of noise and vibration at the helicopter main rotor original photograph by Eurocopter.

The examination of the helicopter main rotor has yielded a multitude of excitation mechanisms for noise and vibration. Dealing with such a complicated system, it is unlikely that a single solution exists to produce relief in all aspects. Thus, a variety of partially very different approaches has been discussed and developed. In this section, the major ideas involving non-active elements will be presented for the classical helicopter configuration. Details on these elements are given by Bielawa [21], Brarnwell et al. [23]. 

The most important part of the transmission is the main gearbox, which contains the most heavily loaded reduction gears transmitting power to the main rotor blades. It is always oil lubricated but a variety of different oils are used in different helicopters. 

Talbot, P.D., Tinling, B.E., Decker, W.A. and Chen, R.T.N., A Mathematical Model of a Single Main Rotor Helicopter for Piloted Simulation, NASA... 

The lateral thrust of the tail rotor of a helicopter has to compensate for the main rotor torque. For maximum effectiveness, it is operated with a rotational speed as high as permitted by the blade tip velocity, but well below the speed of sound. In general, the noise- and vibration-generating mechanisms are similar to those of the main rotor. While there is no cyclic blade pitch, the interaction with the main rotor outflow has to be taken into account. Due to the comparatively small diameter of the tail rotor, its rotational speed is significantly higher than that of the main rotor and thus the emitted noise and vibrations have higher frequencies, see Staufenbiel et al. [168]. 

Figure 74 Schematic of the main rotor blade of Westlands Sea King Helicopter (courtesy of Westland Helicopters Limited), (A) BIM manifold, (B) Root doublers, (C) Erosion shield, (D) Packing piece, (E) Heater mat, (F) Outer wraps, (G) Uni-directional nose moulding, (H) Inner wraps, (J) Uni-directional sidewall slab, (K) Uni-directional backwall slab, (L) Skin, (M) Uni-directional sidewall slab, (N) Honeycomb, (O) Closing Channel, (P) CauUc, (R) Dummy skin, (S) Cuff, (colour version of this figure appears on p. xviLi).

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