Up About Vibration Dynamic Balancing

For the purpose of Propeller Balance, vibration can be described as:
“the unwanted, unproductive, cyclic oscillation of the propeller and
motor assembly about its rotational axis.”

Common effects of propeller imbalance:

Pilot / passenger discomfort
Cracks occurring in onboard panels and mounts
Higher than normal occurrence of motor and prop failures
Physical movement of airframe ('buzz' in the airframe, equipment bays)
Higher than normal occurrence of malfunctioning or failed avionics or instruments
Lowered performance

Vibration excites natural frequencies in other components throughout the airframe and motor assemblies.
The expended energy from vibration causes wear of components, reduced performance, passenger discomfort.

Types of imbalance
There are two types of imbalance that may be present in a propeller.
1. Mass imbalance
2. Aerodynamic imbalance

A mass imbalance is nothing more than an imbalance in a rotating component, normally the propeller, that is located away from center of the rotating mass. The farther from the center of rotation, the greater the imbalance and its destructive force. 
This is the imbalance that we aim
to eliminate or reduce dramatically.

The following chart shows how much oscillating sideload there is at the front crank bearing at 2400 rpm at various levels of vibration. The measure of vibration is IPS (inches per second). 

 

The majority of aircraft tested have a vibration level of above .3 ips.!! 
99% of these could have this eliminated or greatly reduced.


An aerodynamic imbalance, although not common in propeller aircraft, happens when a blade pitch variance occurs from one blade to another during the rotational cycle. If one blade is grabbing more air than any one of the other blades (assymetric thrust), a vibration will be felt. This can and will occur even though any mass imbalance may have already been corrected. This can only be fixed by adjusting,repairing or replacing the prop. We'll detect it, though, if you have it, and
achieve the very lowest vibration levels possible, throughout the highest possible RPM range .

 

  Up About Vibration Dynamic Balancing

 

 

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Last modified: April 04, 2018