Blade Balancing

Having seen Clive Calef's beautifully smooth Piccolo in action at an indoor meet at Potters Bar, I realised my own Piccolo was vibrating excessively. I set about curing the imbalance and was amazed at the improvement. The smoothness allowed me to start doing nose-in flying in the living room.


The first stage is to find the source of the vibration. This can be done using a process of elimination:

  1. First disengage the main motor pinion by pushing down on the rotor shaft . Apply throttle, to drive the tail rotor on its own, and check for vibration.
  2. If the tail rotor is OK, remove the main blades, and re-engage the main pinion so the flybar can rotate. Power up, check the flybar paddles for vibration.
  3. If the flybar is OK, the problem must lie with the main blades.

To balance the main blades properly, you need to balance both statically and dynamically. The technique I adopted does not need weighing scales and although it is not perfectly accurate it made a worthwhile improvement.

Static balancing

The CG of the two blades combined must lie at the centre of the hub in order to balance out centrifugal forces. 

  1. Un-bolt  the blades from rotor head
  2. Temporarily bolt both blades together in-line at the root, using a 5mm nylon bolt  with the head on the top-surface side. Line up the slot in the bolt head so it lies at right angles to the blades.
  3. Support the blades using a 6" steel straight edge along the bolt slot
  4. Apply tape to the trailing edge of the lighter blade, at about 1/3 span, until the blades balance.

Dynamic balancing

Dynamic balancing requires CG of the blades to match each other. Dynamic balance ensures that when the blades bend upwards under load, the centrifugal force of each blade is acting at the same vertical position on the rotor shaft.

  1. Find the CG position of each blade by balancing on the straight edge. Mark this on the blade using a felt-tip pen.
  2. Adjust tape on the other blade, until the CG positions are the same.

Adjustment of Dynamic balance will affect static balance, so you will need to repeat each set of adjustments.

Rotor Head Distortion

On my unit there is a distortion in the rotor head moulding which means that the angle of attack of one blades is about three degrees out. This came as some surprise! Check yours by laying a straight edge under the blade mounting pad, and see if it lines up with the flybar. If not, shim up at the hub as necessary. 

Tracking Adjustment

If after all the above have been checked and there is still excessive vibration, check that the tracking is not grossly out. Place pieces of tape of different colours on each tip to identify the "high" blade.

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