Rotorcraft VRS Avoidance Using Power-Margin Flight Control
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Solution Overview
Problem
Rotorcrafts face challenges in avoiding the vortex ring state (VRS) at low airspeeds, where vertical performance is compromised, and it is difficult for pilots to anticipate the onset of VRS, especially in poor visibility or high workload conditions, leading to control limitations and restricted ability to arrest high descent rates.
Innovation Solution
A system that monitors vertical speed and compares it to a safety threshold, performing VRS avoidance by determining the power margin available from the rotorcraft's engines, limiting vertical speed if the power margin exceeds a threshold, and increasing forward airspeed if it does not, thereby preventing the rotorcraft from entering dangerous flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pilot training and warnings are used to avoid VRS, then pilots can be aware of the danger, but pilots cannot anticipate VRS onset in poor visibility or high workload conditions
Solution Approach 1:
The flight control system automatically monitors vertical speed, determines power margin, and executes VRS avoidance maneuvers without pilot intervention. The system serves itself by detecting dangerous conditions and autonomously adjusting flight parameters, eliminating the need for pilot awareness and action in poor visibility or high workload scenarios.
Solution Approach 2:
The system continuously monitors vertical speed and power margin, comparing actual values against safety thresholds. When VRS conditions are detected (excessive vertical speed at low airspeed with insufficient power margin), the system provides automatic feedback control by adjusting collective pitch or airspeed to exit the dangerous flight regime.
2Reliability
If the system limits vertical speed by adjusting collective pitch, then VRS is avoided, but power margin may be insufficient at low airspeeds
Solution Approach 1:
The system dynamically adjusts the avoidance strategy based on real-time power margin assessment. When power margin is sufficient, the system limits vertical speed through collective pitch adjustment. When power margin is insufficient, the system transitions to increasing forward airspeed as the primary avoidance mechanism, optimizing the approach based on available power.
Solution Approach 2:
The system changes the controlled parameter for VRS avoidance based on power availability. Instead of always limiting vertical speed, the system switches between controlling vertical speed (when power permits) and controlling forward airspeed (when power is limited), adapting the flight parameter being adjusted to match available engine power.
3Speed
If the system increases forward airspeed to avoid VRS, then vertical performance is improved, but this requires sufficient power margin
Solution Approach 1:
The system determines power margin in advance before executing VRS avoidance maneuvers. By assessing available power beforehand, the system can select an appropriate avoidance strategy - either vertical speed limitation or forward airspeed increase - ensuring the chosen maneuver is within available power capabilities.
Data Source
AI summary
A system and method for protecting a rotorcraft from entering a vortex ring state, the method including monitoring a vertical speed of a rotorcraft, comparing the vertical speed to a vertical speed safety threshold, and performing vortex ring state (VRS) avoidance in response to the vertical speed exceeding the vertical speed safety threshold. The performing the VRS avoidance includes determining a power margin available from one or more engines of the rotorcraft, limiting the vertical speed of the rotorcraft in response to the power margin exceeding a threshold, and increasing a forward airspeed of the rotorcraft in response to the power margin not exceeding the threshold.