Helicopter Rotor Track and Balance

Rotor track and balance, or rotor smoothing, is a routine maintenance task that involves a calculated system of adjustments to pitch links, blade weights, and trim tabs. These adjustments are designed to reduce vibrations at the fundamental (once-per-revolution) rotor frequency. A reduction in rotor vibration adds a significant amount of “smoothness” to the aircraft while in flight. In addition, proper smoothing will increase the longevity of the aircraft. The procedure for rotor smoothing is typically performed in multiple flight modes, including flat pitch ground running at 100% (FPG100), hover, and several pre-defined, steady, level flight airspeeds. The slightest adjustment can change both the dynamic balance as well as the aerodynamic response of each individual blade.

Rotor track and balance is a vital process for maintaining an aircraft’s health. A correctly adjusted rotor system will raise pilot comfort levels and increase the lifetime of time-based components prior to replacement.

Rotor smoothing is typically performed with the use of accelerometers mounted in tht cockpit. The accelerometers are synchronized with a tachometer and a tracking device such as a camera or a strobe. The goal is for each blade to trace the same path through the air as it rotates about the hub. HUMS collect the accelerometer, track, and phase information and use a linear model or a neural network to provide solutions that will effectively reduce the vibrations and/or blade track split.

HUMS provide the maintainer with a rotor smoothing solution that gives precise instructions on what type of adjustment to perform (weight, pitch link, tab bend, elastomeric wedge), where to perform the adjustment, and what magnitude of adjustment is required. Since HUMS are continuously collecting data, there is no need to perform dedicated rotor track and balance flights. A helicopter can be flown on its normal mission, and rotor smoothing adjustments can be performed upon its return to home base. The adjustments can be confirmed by normal flight operations during subsequent flights. The exception to this method is when maintenance has been performed on the rotor system; in this situation, it may be advantageous to perform dedicated rotor track and balance.