When an airplane comes in with a squawk for an abnormally high vibration level, it can be a frustrating experience for maintenance techs to identify and address the problem. Even if the squawk can be confirmed and the cause narrowed down to an imbalance in the fan rotor, the headache is not over. The traditional engine balancing procedure, a “3-shot plot,” is a labor and time intensive process that cannot even guarantee the best balance solution.
For those who are not familiar with the process of the 3-shot plot, it involves installing known weights onto the fan disk at different locations and measuring the change in vibration magnitudes at each location. From these vibration levels, it is possible to calculate an approximate balance solution by hand.
All in, a 3-shot plot procedure will normally consist of over 25 steps and involve running the engine at least 4-5 times. With all the effort involved in a 3-shot plot, it is not uncommon for the 3-shot to become shortened to a 2-shot procedure when a lucky weight installation during the process reduces the vibration magnitude below the manufacturer limitation. Even though convenient, this shortened 2-shot shortcut is likely not the most effective balance solution.
With the advanced analytical tools included with a PBS eXpress, the time it takes to identify the cause of a vibration complaint takes significantly less troubleshooting time. Furthermore, if a fan balance is determined to be a cause of unsatisfactory vibrations, the PBS’s Balancing Wizard will quickly determine the best possible balance solution after only a single additional run after the initial baseline.
To see how much this capability can save you, we have developed this small calculator (below), which lets you calculate the savings for each balance and how those savings can quickly stack up throughout the year.
NOTE: We have prepopulated the calculator with some default values to help you get started. Feel free to plugin your own numbers.