Gyroscopic feathering moments and the 'Bell Stabiliser Bar' on helicopter rotors

Simons, I.A. and Modha, A.N. (2002) Gyroscopic feathering moments and the 'Bell Stabiliser Bar' on helicopter rotors. 28th European Rotorcraft Forum, Bristol, UK. 16 - 19 Sep 2002. 8 pp .

Record type: Conference or Workshop Item (Paper)

Abstract

Rotor blade feathering moments caused by the gyroscopic forces acting during helicopter pitching and rolling motions are identified. The consequent blade elastic feathering motion incurred by these moments are shown to give rise to blade flapping which reduces the pitch/roll cross-coupling due to the aerodynamic effects of pitch and roll motions. For blades of low feathering stiffness this reduction is considerable. Inclusion of this effect into rotor analysis can account for much of the difference between calculated cross-coupling and observed flight behaviour. This suggests that 'dynamic inflow' or other effects introduced to explain these discrepancies, should be re-evaluated.
The 'Bell Bar' rotor system is reviewed and it is shown that the stabiliser bar may be considered as an extension of the rotor blade, and gyroscopic feathering moments are a fundamental reason for its operation as a beneficial influence on helicopter flight behaviour.

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