Coaxial Rotor Lift Control to Prevent Retreating Blade Stall
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Solution Overview
Problem
Conventional rotorcrafts are limited in maximum air velocity due to retreating blade stall (RBS) and transonic/supersonic airflow, which restricts their operational efficiency and stability.
Innovation Solution
A coaxial rotorcraft system with electronically controlled electric motors and actuators that precisely control rotor angular velocity and blade angle of attack, using real-time data from sensors to maintain lift and thrust, thereby preventing RBS and mitigating adverse aerodynamic issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If rotorcraft increases air velocity, then operational efficiency and payload are improved, but retreating blade stall occurs limiting maximum velocity
Solution Approach 1:
The system dynamically adjusts rotor blade pitch angles in real-time based on measured air velocity and calculated airflow conditions. The control system continuously modifies blade geometry to maintain optimal angle of attack across all blade positions, preventing retreating blade stall while enabling higher forward velocities.
Solution Approach 2:
The system employs sensors to measure air velocity and continuously calculates airflow over advancing and retreating blades. This feedback is used by the control system to adjust blade pitch angles, creating a closed-loop control that prevents retreating blade stall and maintains stable operation at higher velocities.
2Productivity
If rotorcraft increases air velocity, then productivity is improved, but transonic and supersonic airflow causes blade inefficiency and potential damage
Solution Approach 1:
The control system calculates predicted airflow velocities over rotor blades based on current air velocity and rotor parameters. Before transonic or supersonic conditions are reached, the system proactively adjusts blade pitch angles to reduce angle of attack on advancing blades, preventing harmful airflow conditions before they occur.
Solution Approach 2:
The system replaces conventional fixed-blade or mechanically complex variable-blade systems with an electronically controlled pitch adjustment system. This allows precise, rapid modification of blade geometry to optimize airflow conditions and avoid transonic/supersonic effects.
3Device complexity
If conventional rotorcraft uses fixed blade pitch, then device complexity is reduced, but maximum air velocity is limited due to aerodynamic constraints
Solution Approach 1:
The system replaces complex mechanical variable-pitch mechanisms with electronically controlled actuators that adjust blade pitch angles. This substitution reduces mechanical complexity while enabling dynamic adaptation to higher velocities, allowing the rotorcraft to operate beyond conventional speed limits.
Solution Approach 2:
The system dynamically changes blade pitch angle parameters in response to air velocity changes. By continuously adjusting these parameters based on real-time measurements and calculations, the system maintains optimal aerodynamic performance across a wider velocity range than fixed-pitch systems.
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
Enables rotorcraft operation at significantly higher velocities than conventional systems, allowing for increased payload and reduced mechanical complexity, while preventing retreating blade stall and transonic/supersonic airflow, thus enhancing stability and efficiency.
Implementation Method 1
The lift generated by a rotor blade is calculated by the lift equation for the rotor disk
Implementation Method 2
a horizontal component that causes the rotorcraft to move horizontally and accelerate in a horizontal direction
Data Source
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AI summary
The present disclosure is directed to a method for controlling rotors of a rotorcraft system comprising the steps of: receiving air velocity data, first and second rotors rotational angular velocity data, external air temperature data and rotorcraft altitude data by the control module; calculating air velocity over the plurality of blades based on the received data using the control module; calculating, based on the calculated air velocity, if one or more retreating blades of one of the first and second counterrotating rotors are generating insufficient lift; and sending one or more actuation signals from the control module to the electric motor and/or actuators of the other of the first and second counterrotating rotors to maintain a predetermined amount of lift.