Coaxial Rotor Low-Speed Mixing Algorithm
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Coaxial rotorcraft experience undesirable rolling moments during low-speed forward flight due to asymmetric lift distribution, which complicates yaw control and flight stability, as the advancing side of each rotor experiences greater lift than the retreating side when collective pitch is changed, leading to unbalanced roll moments.
Innovation Solution
A method and system for determining estimated rotor mixing command signals that decouple rolling and pitching responses by using a low-speed mixing algorithm, which combines differential collective and ganged pitch/roll mixing signals with unmixed command signals, incorporating yaw commands, sideslip angles, airspeed, and gain values to produce balanced flight responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If differential collective pitch control is used for yaw control during low-speed flight, then yaw control is achieved, but undesirable rolling moments are generated due to asymmetric lift distribution
Solution Approach 1:
The flight control computer calculates and applies mixing signals before the differential collective command is executed. By pre-calculating the rolling moment compensation based on current flight conditions (airspeed, sideslip angle, yaw rate), the system proactively counteracts the undesirable roll effects before they manifest, allowing yaw control while maintaining flight stability.
Solution Approach 2:
The patent introduces mixing signals as an intermediary between the pilot's differential collective input and the actual blade pitch control. This mixing signal acts as a mediator that transforms the yaw control command into a corrected command that compensates for asymmetric lift distribution, thereby eliminating the harmful rolling moments while preserving the intended yaw control function.
2Force
If collective pitch is increased to generate more lift, then lift is increased, but rolling moments become unbalanced due to dynamic pressure differences between advancing and retreating sides
Solution Approach 1:
The mixing signal applies different pitch corrections to different parts of the rotor system. By calculating the asymmetric lift distribution based on local conditions (advancing vs. retreating sides, different rotor positions in coaxial configuration), the system applies localized compensation that maintains overall lift while balancing the rolling moments across the rotor disk.
3Stability of the object's composition
If mixing signals are calculated and applied to compensate for asymmetric lift, then rolling moments are decoupled, but control system complexity increases
Solution Approach 1:
The patent replaces complex mechanical linkages and physical mixing mechanisms with electronic calculations performed by the flight control computer. The mixing signals are generated through software algorithms that process flight condition data and produce corrected pitch commands, eliminating the need for additional mechanical mixing hardware while achieving the same decoupling function.
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 solution effectively decouples rolling and pitching moments, enhancing flight stability and response by applying differential collective to ganged mixing signals, resulting in improved control and reduced rolling moments during low-speed flight.
Implementation Method 1
the advancing side of the rotor tends to create more lift than the retreating side when the collective pitch is changed
Implementation Method 2
Due to dynamic pressure differences on the advancing versus retreating sides, the advancing (RIGHT) side sees greater increase in lift
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A system and method for estimating rotor mixing commands for an aircraft includes receiving signals indicative of reference commands from one or more controllers; receiving signals indicative of airspeed and sideslip angle for the aircraft, the sideslip angle being indicative of a direction of flight for the aircraft; calculating a sine and cosine of the sideslip angle; determining gains for roll and pitch as a function of the airspeed, the determining including referencing a look-up table that indexes the gain constants with the airspeed; and determining the one or more rotor mixing commands from the determined gains, the one or more rotor mixing commands being applied synchronously to the rotors in the aircraft.