Contra-rotating Propeller Balancing via Hub Envelope Counterweights
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Solution Overview
Problem
Contra-rotating propellers in propulsive systems experience radial unbalance due to the deviation of their center of gravity from the axis of rotation, leading to mechanical vibrations that are not adequately addressed by existing balancing methods, especially under aerodynamic forces during flight.
Innovation Solution
Counterweights are strategically placed on the hub envelopes, close to the ends of the propellers, both radially and axially, to correct radial and axial unbalances, allowing for precise and accessible manual balancing without affecting aerodynamic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If counterweights are arranged on locations provided on the propulsive system in the plan of each propeller, then the center of gravity of each propeller can be repositioned to reduce radial unbalance, but the balancing is frequently found insufficient when the propulsive system is in flight due to additional aerodynamic forces and moments
Solution Approach 1:
The patent extends the balancing approach from a single plane (the propeller plan) to multiple dimensions by positioning counterweights on hub envelopes at locations distant from the propeller plans, both radially and axially. This three-dimensional positioning allows counterweights to effectively counteract both radial unbalance and axial unbalance caused by aerodynamic forces during flight, resolving the insufficiency of traditional plan-based balancing.
2Measurement precision
If counterweights are arranged distant both radially and axially from the centre of gravity of each propeller on hub envelopes, then forces and moments can be generated to precisely correct radial and axial unbalancings, but the locations must be accessible for manual balancing
Solution Approach 1:
The hub envelope serves as an intermediary structure that provides accessible locations for mounting counterweights. By positioning counterweights on the external surfaces of the hub envelopes, the patent enables easy manual access for balancing operations while maintaining the desired radial and axial distances from the propeller centers of gravity, thus achieving both precision and ease of operation.
3Productivity
If counterweights are positioned on hub envelopes at ends distant from propeller plans, then space availability is optimized and aerodynamic performance is maintained, but the locations must provide sufficient leverage for balancing
Solution Approach 1:
The patent utilizes the three-dimensional space around the propeller hub by positioning counterweights on the hub envelopes at locations distant from the propeller plans in both radial and axial directions. This multi-dimensional positioning maximizes the use of available space while generating sufficient balancing moments through the increased lever arms, achieving both space optimization and effective balancing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces mechanical vibrations by precisely repositioning the center of gravity, ensuring stable operation during flight while optimizing space usage and maintaining aerodynamic performance.
Implementation Method 1
the centre of gravity of each propeller is adapted to be deviated from the axis of rotation thereof, thereby resulting, upon its rotation, in a radial unbalance phenomenon... the counterweights being arranged, in the propulsive system, distant both radially and axially from the centre of gravity of each propeller, it results in the generation of forces and moments being able to precisely correct the radial and axial unbalancings
Implementation Method 2
such unbalance is able to generate mechanical vibrations being able to be transmitted to a piece of equipment—in particular the nacelle of an aircraft receiving passengers—to which the propulsive system is attached, which can be unpleasant for them
Data Source
AI summary
In order to eliminate or at least to reduce a possible unbalance of the propulsive system, counterweights are brought in locations that are provided on the hub envelope, near the ends of the latter and away from the planes of the propellers. More particularly, the counterweights are provided as discrete elements located in two planes spaced from the propellers and orthogonal to an outer surface of the hub envelopes, or are provided as a non-uniform mass ring.