Rotor Balancing

Data acquisition systems, recorders, spectrum analyzers RL-C21M

Vibration control systems RL-C21

Vibration control systems RL-C25

Data acquisition systems, recorders, spectrum analyzers RL-R19

Data acquisition systems, recorders, spectrum analyzers RL-R17

Software Sensor Calibration

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Solution

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.

Remote control

To simplify the procedure for the crew, we used a remote control to run RL-R19. It has the necessary minimum of control tools and LED indicators.

Start of balancing

The first step was the initial run. The helicopter performed a standard flight procedure in several modes.

The following flight modes were selected as the relevant ones

Hover

In this diagram you see the position of 5 blades and a number of points, which show the unbalance vector at a particular time.

The red cross shows the averaged value of unbalance.

Forward flight 100 km/h

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.

Forward flight 200 km/h

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.

Balancing

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:

1803.1 g on the first blade (the actual weight mounted - 1800 g)
432.88 g on the second blade (the actual weight mounted - 400 g)

The control run showed that the vibration level was decreased by 1.8 – 3.3 times.

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

Our equipment performs highly accurate helicopter tuning in the required flight modes. To achieve that, all the measurements and calculations should be made in the corresponding modes. This approach may create greater vibration levels in other flight modes but maintain very good results in the main mode of operation.