Propellers can also be dynamically balanced (spin balanced) with an analyzer kit to reduce the vibration levels of the propeller and spinner assembly. Some aircraft have the system hardwired in the aircraft and on other aircraft the sensors and cables need to be installed before the balancing run. Balancing the propulsion assembly can provide substantial reductions in transmitted vibration and noise to the cabin and also reduces excessive damage to other aircraft and engine components. The dynamic imbalance could be caused by mass imbalance or any aerodynamic imbalance. Dynamic balancing only improves the vibration caused by mass unbalance of the externally rotating components of the propulsion system. Balancing does not reduce the vibration level if the engine or aircraft is in poor mechanical condition. Defective, worn, or loose parts will make balancing impossible. Several manufacturers make dynamic propeller balancing equipment, and their equipment operation could differ. The typical dynamic balancing system consists of a vibration sensor that is attached to the engine close to the propeller, and an analyzer unit that calculates the weight and location of balancing weights.
Dynamic propeller balancing is a vital factor in maintaining an airplane’s service life. Strict guidelines determine tolerances for optimal performance and safe operation. Even with regular maintenance and attention to these limits, the dynamic components for a propeller system can become imbalanced. Small balance issues can quickly stack up to create errors that affect the aircraft engine and propellers.
Propeller Balance and Vibration
An unbalanced propeller system, including spinner assembly, can cause vibration that is detectable through testing or even in-cabin by the flight crew. While annoying, the noise and movement transmitted by these vibrations are the least of the problems that can manifest. Numerous minor issues, such as cracked sheet metal, persistent avionics failures, thrown belts, and excessive light bulb failures, can be corrected by balancing. Catastrophic damage to the engine power train and other dynamic components can also occur if the imbalance isn’t addressed properly.
Fixing Dynamic Propeller Balance
While not a universal “fix-it” for eliminating vibration, its effects can often be reduced through propeller smoothing and balancing of the propeller assembly. Spin trim balancing may also help improve some vibration due to unbalanced components. If an aircraft or its engine is already in poor shape, however, balancing won’t help as the parts may be too old, worn, and in need of replacement.
It is still important, though, to perform routine testing for propeller balance, and not just when an issue is reported, in order to avoid future problems. ACES analyzers make it easy to perform Dynamic Propeller Balance testing for quick adjustments and more complex balance jobs.