Tiltrotor Rotor Speed Control for Smoother Mode Transitions
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Tiltrotor aircraft experience abrupt transient torque loads during rapid changes in rotor speed, leading to increased maintenance costs, reduced payload capacity, and occupant discomfort due to the need for reduced weight and fuel margins.
Innovation Solution
A controller system that automatically changes rotor speed from one flight mode to another using a variable acceleration-rate profile, based on operational and environmental parameters, reducing the severity of torque loads by implementing a multi-segment linear, curved, or stair-stepped acceleration profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If rotor speed is changed rapidly from one reference speed to another, then transition time is reduced, but transient torque loads increase causing stress and wear
Solution Approach 1:
The patent applies dynamics by making the acceleration rate variable rather than constant. The controller dynamically adjusts the acceleration rate during the transition based on the current rotor speed and target speed, implementing a profile that starts with higher acceleration when the speed difference is large and reduces acceleration as the target speed is approached. This dynamic adjustment resolves the contradiction by optimizing both transition time and torque load throughout the transition process.
Solution Approach 2:
The patent changes the parameter of acceleration rate from a fixed constant to a variable parameter that changes during the transition. By implementing an acceleration-rate profile where the acceleration rate is a function of time or rotor speed, the system optimizes the balance between transition speed and torque load. This parameter change allows the system to achieve faster transitions while keeping transient torque loads within acceptable limits.
2Strength
If transient torque loads are reduced through slower rotor speed changes, then stress and wear decrease, but transition time increases
Solution Approach 1:
The system uses dynamic acceleration rate adjustment to resolve this contradiction. Rather than using a uniformly slow transition, the controller implements a time-varying acceleration profile that allows faster changes when torque loads are less critical and slower changes when approaching the target speed. This dynamic approach reduces overall transition time while maintaining acceptable torque load levels throughout the transition.
Solution Approach 2:
The patent employs periodic or phased action by dividing the transition into multiple phases with different acceleration rates. The transition process is structured with an initial phase of higher acceleration, a middle phase of moderate acceleration, and a final phase of lower acceleration near the target speed. This phased approach optimizes both transition time and torque load management.
3Device complexity
If reference rotor speed is changed at a fixed rate, then control simplicity is maintained, but abrupt transient torque loads occur at the beginning and end of transitions
Solution Approach 1:
The patent transforms the control approach from a simple fixed-rate change to a dynamic acceleration-rate profile. The controller implements a more complex control law that calculates and applies varying acceleration rates based on the current state and desired trajectory. This increased control complexity eliminates the harmful abrupt torque loads by ensuring smooth acceleration and deceleration throughout the transition.
Solution Approach 2:
The system applies beforehand cushioning by preparing for the transition with a planned acceleration profile that anticipates and cushions against potential torque shocks. The controller pre-calculates the acceleration rates to avoid abrupt changes, effectively cushioning the system against harmful transient loads before they can occur. This proactive approach smooths out the torque profile throughout the entire transition.
Data Source
AI summary
A method and system to control a rotor system includes providing a controller communicably coupled to the rotor system, and automatically changing a rotor speed of the rotor system from a first rotor speed in a first flight mode to a second rotor speed in a second flight mode over a time period using the controller in accordance with an acceleration-rate profile that varies over the time period.