Tiltrotor Rotor Speed Transitions Using Variable Acceleration Profiles
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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 safety margins.
Innovation Solution
A controller system that automatically changes rotor speed from one flight mode to another using a variable acceleration-rate profile, which can include multi-segment linear, curved, or stair-stepped profiles, to minimize torque loads by gradually increasing and decreasing acceleration rates.
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, using a higher initial rate to reduce overall transition time while tapering the rate near the end to minimize torque loads. This dynamic adjustment resolves the contradiction between fast transition and low torque loads.
Solution Approach 2:
The patent uses preliminary action by anticipating the torque load issue before it occurs. The controller is programmed with a predetermined acceleration profile that automatically reduces the acceleration rate as the rotor speed approaches the target reference speed. This preliminary planning prevents excessive torque loads without requiring reactive adjustments.
2Strength
If transient torque loads are reduced through slower acceleration, then stress and wear decrease, but transition time increases
Solution Approach 1:
The patent resolves this contradiction by making the acceleration rate dynamic rather than static. The controller continuously adjusts the acceleration rate based on the current rotor speed and remaining distance to the target reference speed. This allows the system to achieve both reduced stress/wear and acceptable transition time by optimizing the acceleration profile in real-time.
Solution Approach 2:
The patent applies parameter changes by modifying the acceleration rate parameter during the transition process. Instead of maintaining a constant acceleration rate, the controller changes the acceleration rate parameter as a function of rotor speed and time, allowing the system to adapt to varying torque load conditions while maintaining efficient transition timing.
3Reliability
If safety margins are increased to handle transient torque loads, then reliability improves, but payload capacity decreases
Solution Approach 1:
The patent uses preliminary action by pre-programming the acceleration profile to anticipate and prevent excessive torque loads. This proactive approach ensures reliability is maintained through controlled acceleration while avoiding the need for excessive safety margins that would reduce payload capacity. The system plans the transition in advance to achieve both goals.
Solution Approach 2:
The patent applies parameter changes by optimizing the acceleration rate parameter to achieve the minimum necessary safety margin for reliable operation. By precisely controlling the acceleration profile, the system maintains adequate safety margins without over-engineering, thereby maximizing payload capacity while ensuring reliability.
4Productivity
If acceleration rate is increased to reduce transition time, then productivity improves, but transient torque loads cause occupant discomfort
Solution Approach 1:
The patent applies dynamics by making the acceleration rate variable rather than constant. The controller dynamically reduces the acceleration rate as the rotor speed approaches the target reference speed, minimizing torque loads and occupant discomfort during the critical final phase of transition while maintaining high productivity through optimized initial acceleration phases.
Solution Approach 2:
The patent uses parameter changes by adjusting the acceleration rate parameter based on the transition phase. The controller changes the acceleration parameter from high values during early transition to low values near the end, achieving both high productivity and minimal occupant discomfort through intelligent parameter management.
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A method (600) and system (650) to control a rotor system (660) includes providing (602) a controller (652) communicably coupled to the rotor system (660), and automatically changing (604) a rotor speed of the rotor system (660) 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 (652) in accordance with an acceleration-rate profile that varies over the time period.