Contra-rotating rotors with dissimilar blade counts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Contra-rotating coaxial rotors in rotorcrafts generate undesirable noise due to overlapping rotor blades and air vortices, which existing designs fail to adequately mitigate, and they also face issues with retreating blade stall and roll moment balance.
Innovation Solution
The use of a rotorcraft design with a first rotor and a second coaxial rotor having a different number of blades, where the rotors are contra-rotated to minimize overlap and noise, with the first rotor having a higher blade count than the second, and the rotors are positioned to reduce noise by maintaining a constant gap and utilizing a ducted rotor system with a frustoconical profile to reduce noise from unsteady flow interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If contra-rotating coaxial rotors with similar blade counts are used, then lift is generated and fuselage rotation is prevented, but noise is generated due to overlapping rotor blades and air vortices
Solution Approach 1:
The patent applies asymmetry by configuring the first rotor with a different number of blades than the second rotor. Specifically, the first rotor has a first number of blades while the second rotor has a second number of blades that is different from the first number. This asymmetric blade configuration prevents the rotor blades from overlapping at consistent intervals during rotation, thereby reducing periodic noise generation while maintaining the contra-rotation benefits of eliminating tail rotor requirements and preventing fuselage rotation.
2Object-generated harmful factors
If contra-rotating coaxial rotors are used to eliminate tail rotor, then vehicle roll moment balance is maintained, but noise is generated from blade overlap and vortex interaction
Solution Approach 1:
The patent employs asymmetry by designing the contra-rotating coaxial rotors with different blade counts. The first rotor comprises a first number of blades and the second rotor comprises a second number of blades, where these numbers differ. This asymmetric configuration disrupts the periodic overlap pattern that would occur with identical blade counts, thereby reducing noise from blade overlap and vortex interaction while maintaining the simplified tail rotor-less design.
3Object-generated harmful factors
If contra-rotating rotors with different blade counts are used, then noise is reduced by minimizing blade overlap, but rotor design complexity increases
Solution Approach 1:
The patent applies asymmetry by configuring the first rotor with a first number of blades and the second rotor with a second number of blades that differs from the first. This asymmetric blade count configuration prevents synchronized blade overlap and reduces interaction noise between the contra-rotating rotors. The different blade counts ensure that blades from the first rotor do not consistently intersect with blades from the second rotor, thereby minimizing vortex interaction and noise generation.
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
This design reduces noise by minimizing blade overlap and interaction noise, while maintaining lift and balance, and eliminates the need for a tail rotor system by utilizing contra-rotation to stabilize the fuselage, resulting in a more efficient and quieter flight.
Implementation Method 1
Some rotorcraft utilize contra-rotating coaxial rotors on a main mast to create lift
Implementation Method 2
using the contra-rotating coaxial rotors reduces or removes a need for a tail rotor system or any other system for preventing rotation of a fuselage about the main mast axis
Implementation Method 3
undesirable noise associated with the rotor blades of a first rotor repeatedly overlapping the rotor blades of a second rotor and the rotor blades of the second rotor passing through air vortices generated by the first rotor
Data Source
AI summary
A rotor system has a mast axis, a first rotor rotatable about the mast axis in a first direction and the first rotor has a first number of first rotor blades, and a second rotor rotatable about the mast axis in a second direction and the second rotor has a second number of second rotor blades that is different than the first number. The second direction is opposite the first direction.