I’ve lately been involved in three helicopter “return to service” projects requiring blade tracking and balancing and have heard different versions of how this needs to be carried out. So I decided to follow along with a no-nonsense Canadian helicopter company while they complete a routine blade tracking and balancing exercise.
The night before the crew had installed the blades. 9 am the next morning the engineer preps the helicopter.
A young pilot completes the pre-flight and pre-start check for the first ground run.
The engineer sets up the Chadwick Helmuth Vibrex 2000 Plus analyzer and ensures it is working properly.
The pilot fires up the Bell 206 for the first idle run up whereas the engineer can determine where on the graph the balance center falls.
We discover it is off in both the vertical and lateral.
The engineer tackles the tracking first by making adjustments on the rotor head. After several ground runs he is satisfied.
Then he concentrates on getting the vertical balance into center by adding or subtracting counter weights to effect the mass. After a few 100% ground runs we get the vertical perfectly aligned on the graph. Next the Chief Pilot comes out and carries out a hover and flight test to finalize the tracking.
We find that the blade tracking is off slightly and we can feel it in the hover. We then carry out 50 knot and 80 knot tracking to determine how much to change the trim tabs. The blades are slightly off causing a noticeable vibration in flight.
On the ground again the engineer makes a 1 degree adjustment by bending the blade trim tab down 4 degrees whereas it rebounds back to the new adjustment of 1 degree down.
The Chief Pilot starts up again and lifts off into a hover. The helicopter has a noticeable vibration and during the flight test the shake is still noticeable. The engineer plots the change and realizes that he has adjusted in the wrong direction.
He readjusts in the opposite direction and the Chief Pilot carries out a final hover and flight test. The Chadwick shows the tracking is now dead on with no serious vibration in flight. The whole exercise took about 3 hours. After that we all went for lunch.