Downloaded from https://www.everyspec.com ADS-79D-HDBK aerodynamic drag, and induced lift. The adjustment for lateral corrections is made by adding or subtracting weight from the rotor blade or hub assembly with a secondary effect of adjustments to pitch change links. Out-of-plane vibrations are primarily caused by unequal lift of the rotor blades and corrections result in adjustments primarily to trim tab angles with a secondary effect of adjustments to pitch change links. Blade track height corrections are most strongly affected by adjustments to pitch change links. The process of rotor smoothing consists of three steps; blade tracking, rotor balancing, and final rotor smoothing.
The goal of initial blade tracking is to obtain a small blade track split, which is most important when one or more blades are newly installed on the aircraft. Blade tracking can be performed on the ground or in hover, and at one or more rotor speeds from idle to full speed. It ensures that vibration levels will not be wholly unreasonable due to large blade track differences prior to proceeding to the next step. Once acceptable conditions have been obtained in the blade tracking step, the aircraft is ready for rotor balancing.
The goal of rotor balancing is to reduce any residual lateral vibrations which were not corrected in the static balancing process or are a result of minor differences in aerodynamic drag. Rotor balancing can also be performed on the ground or in hover, and at one or more rotor speeds from idle to full speed. Once acceptable conditions have been obtained in the rotor balancing step, the aircraft is ready for final rotor smoothing. The goal of final rotor smoothing is to obtain the lowest possible vibration levels while maintaining a reasonable blade track split.
Vibration levels are considered in both in-plane and out-of-plane directions and across multiple aircraft operating conditions from on the ground, to in hover, to various forward flight speeds. Depending upon the primary mission of the aircraft and the opinion of the user community, vibration direction (in-plane versus out-of-plane) and operating state (hover versus forward flight) can be weighted differently to achieve the most acceptable vibration levels. Many rotor smoothing algorithms exist. The algorithms use as input the measured vibrations and the blade track, and output a set of recommended rotor adjustments to minimize both. Examples of these algorithms are: a. Neural Networks b.
Simultaneous Linear Equations c. Statistical Methods The algorithms also take into consideration practical constraints on the recommended adjustments such as: a. Upper Limits to adjustments based upon physical constraints (i.e. maximum change in pitch link length due to number of available threads on the pitch link barrel) b. Lower limits to adjustments based upon physical constraints (i.e. minimum change in blade weight due to the weight of an individual washer) c. Quantizing adjustments based upon practical measurement levels (i.e.
bending a trim tab to increments of Ѕ of a degree) Smoothing of the main rotor system is complex due to the multiple physical differences in rotor blades which result in differences in vibration and blade track height, and is important in reducing both in and out-of-plane vibrations levels experienced by the aircrew. Smoothing of the tail rotor system is 109