For this case, we offered RL-R19 to be used as a DAQ-system. We mounted the accelerometer next to the pilot’s seat and an optical tachometric sensor on the dashboard. Some reflective tape was stuck on the first blade. If the equipment is placed this way, it is possible to measure the phase and amplitude of the imbalance vector in any flight mode.
The positioning of points close together means that the increased level of vibration is due to the main rotor unbalance. The distance of points from the center and the space occupied by the cloud of points tells us that the balancing procedure has good chances of being a success.
Even though the unbalance vector has slightly changed, the cloud of points is still dense and located in about the same segment of the diagram. It shows that the nature of the unbalance is fixed, e.g. it is due to the uneven mass distribution in the rotor and does not depend on the flight mode.
To determine the “heavy point”, the trial weight of 500 g was placed on the first blade of the main rotor.
After that, the unbalance vector shifted very little in phase, which signifies that the corrective weight is to be placed around the angle of the first blade. It was calculated that the mass of the corrective weight is 1980.14 g and the angle of its placement is 12⁰.
The corrective weight was split onto two nearby blades:
Vibration, mm/s |
Hovering |
100 km/h |
200 km/h |
---|---|---|---|
Before balancing |
5.56 |
4.11 |
6.24 |
After balancing |
2.15 |
1.25 |
3.49 |