Downloaded from https://www.everyspec.com ADS-79D-HDBK usually simplified in that only the in-plane vibration is considered; measurements of the out-of-plane vibration or tail rotor blade track are usually not acquired. Thus, tail rotor smoothing is usually referred to as tail rotor balancing. Likewise, smoothing of any driveshaft considers only in-plane vibration and is therefore referred to as shaft balancing. The quality of the indications from the installed rotor smoothing hardware is important for good recommendations to be made. Diagnostic algorithms should be employed on board that indicate to the maintainer the quality of the measured tachometer, track, and vibration data.
This should also be taken into account when making adjustment recommendations to the user, where low quality data should be given less emphasis than high quality data. During dedicated rotor smoothing flights, data quality should be made available to the pilot so that low data quality acquisitions can be re-flown prior to aircraft shut down. Algorithms that learn from rotor adjustments made in the field should be scrutinized carefully by the Project Manager and the Airworthiness Authority. Mistakes made in the rotor smoothing process and learned by the system incorrectly will result in faulty information and thus learning algorithms must be employed carefully.
For rotor harmonics that are associated with the blade pass frequency, legacy aircraft typically use passive vibration control measures to improve crew comfort. These vibration absorbers are usually of the tuned mass/spring style applied in many high vibration environments to transportation and civil structures. DSCs can be used to ensure the proper operation of these devices or can be used to tune these devices by generating recommendations for maintainers. New production and future aircraft may be equipped with active vibration control systems with force generators and airframe sensors.
The force generators are thus used in place of the passive vibration absorbers to reduce the blade pass frequency vibration. Benefits could be achieved by linking these control systems with the DSC to measure and report the effectiveness of the control system. 110