[rotorwrench]

This is off topic a bit but I wanted to add it in since it relates to crankshafts & flywheels. Some of the helicopters I work on have a crankshaft driven fan that is either directly attached to the drive end of the crankshaft or attached through an extension shaft and bearing assembly. The one that is directly attached is generally only balanced when an imbalance is suspected or after a related part is replaced. The ones with the extension have to be checked any time they are removed and reinstalled for maintenance due in large part to the use of a tapered shaft.

I use the same balance machine that is used for rotor balance in the T/R configuration. The accelerometer or vibration sensor is mounted vertically pointing up on engine nose case for directly attached flywheel fans or on the extension shaft bearing housing for those types pointing down. The accelerometer will work the same either way since it receives vibration in a 360 degree plane. The balance machine is just a small electronic box with an IPS meter and several function switches & buttons that is all powered by a 12 or 24 volt battery. I won't get into it's function other than the fact that this particular model does use a strobe light to get the angle of imbalance movement around the crankshaft's circumference.

Before the ground run, a piece of reflective tape is installed at any point on the flywheel or fan to use as a reference for where the imbalance is. The machine is set to the full speed rpm of the applicable engine in the test. The engine ground run is started and it's eventually run up to operating rpm. The strobe light is used to see what clock angle the reflective tape is at while the balance machine is further tuned to the actual RPM. The IPS meter reading is recorded and the test is complete with the normal shut down procedure.

After shut down, the crankshaft is rotated till the location of the reflective target tape is in the same clock angle location that was observed during the test run. Designated by where the accelerometer is mounted in relation to the clock angle of the shaft, the place where the weight will be added is either 12 o'clock or 1 o'clock depending on the application. The manufacturer of the aircraft has a chart that is read using the IPS reading and it will instruct how much weight is to be added to correct the imbalance condition. When the weight installation is complete. The engine ground run vibration check is performed again to see if the imbalance was eliminated or not. If it is not at least 0.2 IPS or less, the weight will be adjusted again until it is within acceptable limits with a further balance run check.

This process is done on propellers of airplanes as well as rotors and engines of helicopters. Turbine engines are checked but obviously no adjustments can be made externally but it will let the maintainers know the condition of the turbine hot section and compressor rotors. When I was working in turbine overhaul some years ago, I worked with a Balreco balance machine to balance the turbine and compressor rotors before the engines were reassembled. It also used a strobe light and an IPS meter to find the imbalance location, I used soft wax added to the light side to balance each end of the rotor so that I would have a reference as to how much weight had to be removed from a point that was 180 degrees from the light side (heavy side). There was a protruding ring on the rotors where metal could ground off to correct the imbalance. A person has to be real careful while grinding on $5k rotor wheel. The wheels are likely a lot higher in price now days.