McFadden Control Loading

The cyclic stick control forces are provided by a McFadden Systems Inc. Model 292B Universal Variable Digital Cockpit Control Force Loading System. The stick forces are generated by rotary servo actuators of the limited rotation vane type with hydrostatic bearings. An electro-hydraulic servo valve controls each of the two actuators using analog electrical signals fro the digital unit’s digital-to-analog converter. Differential pressure and angular position transducers are used to provide feedback for the force and modeling loops. A digital control loop closes the force generation process with a 5 kHz update rate. The manufacturer specifies a 80 Hz bandwidth for this loop. The mathematical model that generates force commands to the system in response to stick displacement also runs at 5 kHz (see Section 8.1.2). This model can have its parameters updated in real-time at up to 1 kHz.

The system can generate a maximum force of ±150 lb at the stick’s hand grip on both axes. The maximum pitch displacement is ±15.3˚ (±7.37 in) and the maximum roll displacement is ±15.5˚ (±7.47 in). The force resolution is better than 0.1 lb at the hand grip.

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