Solution
After the helicopter had been assembled, it underwent the standard procedures of blade tracking and main rotor dynamic balancing. However, the crew still experienced a very uncomfortable level of vibration.
As the standard procedure at the factory only took into account the vertical vibration, we assumed that after the balancing procedure the vibration level on the other axes could have increased.
New measurements were made using a 3-axial accelerometer and RL-R19 DAQ-system.
The results turned out to be as predicted
In spite of the fact that the vertical vibration was insignificant, the vibration on longitudinal and lateral axes was too great, hence the complaints of the crew.
Preparation
All the corrective weights previously placed on the blades of the main rotor were removed, in order to run the dynamic balancing procedures with all three axes taken into account.
The initial level of vibration without corrective weights was the following:
Balancing algorithm
We decided to perform the balancing of the lower rotor first, and then make adjustments to minimize the corrective weights to be placed on the upper rotor, since the influence of the upper rotor unbalance is greater due to longer arm of force
Lower rotor balancing
As the helicopter is small, we used sets of spacers as corrective weights. Based on the results of measurements and calculations, the weight of 8 g was mounted on the lower rotor.
The vibration level after the balancing lowered
Upper rotor balancing
The upper rotor balancing was performed in the hover mode.
Aftre the calculations a corrective weight of 3 g was placed on the upper rotor.
Balancing results after control hover were the following
The vibration level was decreased by 1.5 – 2.0 times.
