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Fatigue testing rotor heads
FATI6UE REPORTS Fatigue testing rotor heads Completed in the middle of last year was a universal helicopter rotor head fatigue testing facility at the Yeovil factory of Westland Helicopters. The complete multi-channel, computercontrolled servo-hydraulic loading system, together with the hydraulic supply and ring main, was supplied by Carl Schenck (UK) Limited. In order to clear any new design of rotor head for flight, the complete head must be fatigue tested with typical dynamic loads. This new facility covers the testing of rotor
heads with any number of blades from two to six. Initially it has been set up for testing a four-arm rotor head (see Fig. 1). The load reaction frame is in the form of a large pit, constructed with reinforced concrete, and incorporating a large ring to react thecentrifugal loads; a smaller ring and strong floor react the vertical (flap) and horizontal (lag) loads. A raised base is provided in the centre for mounting the rotor head. This type of construction provides the very stiff reaction required for the various loads
Fig. 1 The load reaction frame of the newly-installedhelicopter rotor head fatigue testing facility at Westland Helicopters' Yeovil factory
and keeps rig deflection at a minimum. In the Westland test rig, 14 hydraulic actuators are used. Eight are used to apply the flap and the lag forces at the blade attachment points. The actuators are used with force feedback and cascade control and each can apply a force up to 100kN with a maximum stroke of 400 mm. The flap actuators currently operate at amplitudes of up to -+175mm with alternating loads of up to -+63 kN. A further four actuators are used to apply the centrifugal loads via steel cables. Each of these is servo-controlled with force feedback and produces a force of up to 220 kN. The remaining two actuators are rome feedback controlled and apply the torque loads to the head. The hydraulic supply for the system consists of eight Schenck hydraulic power packs, giving a total flow of 13201/min at a pressure of 28 MPa. A high pressure distribution system deuvers oil to various distribution points around the test laboratory. The complete loading system is programmed, controlled and monitored by a Schenck Hydropuls computer system which outputs the required test load programmes to the 14 actuator channels. It checks that the correct load levels are achieved and, if necessary, takes programmed actions if the correct loads are not achieved or if other trip functions are exceeded. Printout of the test status is provided at required intervals or when any error function is tripped. A 100 channel HBM data logging system is linked to the computer to monitor strain gauges and transducers fitted to the rotor head.
Carl Schenck (UK) Limited, Stonefield Way, Ruislip, Middlesex HA40JT, England.
INT. J. FATIGUE January 1981 43
heads with any number of blades from two to six. Initially it has been set up for testing a four-arm rotor head (see Fig. 1). The load reaction frame is in the form of a large pit, constructed with reinforced concrete, and incorporating a large ring to react thecentrifugal loads; a smaller ring and strong floor react the vertical (flap) and horizontal (lag) loads. A raised base is provided in the centre for mounting the rotor head. This type of construction provides the very stiff reaction required for the various loads
Fig. 1 The load reaction frame of the newly-installedhelicopter rotor head fatigue testing facility at Westland Helicopters' Yeovil factory
and keeps rig deflection at a minimum. In the Westland test rig, 14 hydraulic actuators are used. Eight are used to apply the flap and the lag forces at the blade attachment points. The actuators are used with force feedback and cascade control and each can apply a force up to 100kN with a maximum stroke of 400 mm. The flap actuators currently operate at amplitudes of up to -+175mm with alternating loads of up to -+63 kN. A further four actuators are used to apply the centrifugal loads via steel cables. Each of these is servo-controlled with force feedback and produces a force of up to 220 kN. The remaining two actuators are rome feedback controlled and apply the torque loads to the head. The hydraulic supply for the system consists of eight Schenck hydraulic power packs, giving a total flow of 13201/min at a pressure of 28 MPa. A high pressure distribution system deuvers oil to various distribution points around the test laboratory. The complete loading system is programmed, controlled and monitored by a Schenck Hydropuls computer system which outputs the required test load programmes to the 14 actuator channels. It checks that the correct load levels are achieved and, if necessary, takes programmed actions if the correct loads are not achieved or if other trip functions are exceeded. Printout of the test status is provided at required intervals or when any error function is tripped. A 100 channel HBM data logging system is linked to the computer to monitor strain gauges and transducers fitted to the rotor head.
Carl Schenck (UK) Limited, Stonefield Way, Ruislip, Middlesex HA40JT, England.
INT. J. FATIGUE January 1981 43