Vortex Ring State (formerly Settling with Power)

Purpose

To understand flight conditions that can cause vortex ring state, and to recognize the signs of vortex ring state and initiate the appropriate recovery.

Description

• Demonstrate vortex ring state and recovery.
• Allow student to develop vortex ring state to recognize signs.
• Allow student to initiate recovery from vortex ring state condition.

Instructional aids and pre-requisites

• Ground Lesson pre-requisites: vortex ring state

Content

• Pre-flight briefing: Discuss conditions where aircraft is most susceptible to VRS
  • Steep approach with a high rate of descent
  • Attempting to maintain an out-of-ground effect hover with insufficient performance
  • Approaches with a tailwind
• Pre-flight briefing: Discuss the requirements for VRS
  • >300 fpm descent, >20% power, and <10 KIAS (below ETL)
• Pre-flight briefing: Discuss signs of VRS and proper recovery
  • Vibration,  reduced control effectiveness, and high rate of descent
  • Reduce collective, add forward cyclic to regain ETL
  • Student should expect a significant, nose-down attitude during recovery and a high sink rate
• Climb to ≥1500 AGL, clear the area, and head into the wind
• Reduce power to 5˝ below power required for hover (or just slow to below ETL while maintaining altitude)
• Maintain altitude and reduce airspeed with aft cyclic until airspeed <20 kias
• Continue decelerating and allow sink rate to increase to ≥300 fpm
• Vibration and decreased control effectiveness indicate the onset of VRS
• Demonstrate that a slight increase in collective at this point will increase vibration and sink rate
• Initiate recovery with forward cyclic to hold a 60 knot attitude
• Simultaneously reduce collective
• When airspeed is ≥ETL, recovery is complete and a climb can be established with an increase in collective
• Repeat the demonstration without the demonstration where collective is raised (ie, just entry and recovery)

Common errors

• Confusing vibration from ETL with VRS
  • When the trim strings drop, you are below ETL
• Excessive nose-down attitude on recovery
• Increasing power before recovery is complete
  • Again, trim strings will come alive again, indicating airspeed is above ETL

Completion standards

• State conditions that can lead to VRS
• Recognize signs of VRS
• Initiate proper recovery

Teaching considerations

• Developing VRS may require a negative ground speed
• VRS is fully developed when descent reaches 700 fpm in the R22 (not that you should attempt to reach this RoD)
• If necessary, autorotation is an instant fix for VRS
• Watching the trim strings is a good indicator for ensuring helicopter is above or below ETL
• Practice this maneuver with excess altitude and personal minimums for when the recovery should be initiated
• Clear below and behind before initiating the maneuver

Additional practice

• None specified

Additional resources

• The 3-2-1 rule is very conservative; SN22 in the R22 POH recommends >30 KIAS until rate of descent is <300 fpm, and a chart in Principles of Helicopter Flight suggests that settling isn’t a risk until ROD >500 fpm, airspeed is <10 KIAS, and a steep angle of approach is being used (>50 degrees).
• Also note that there is a bit of a debate about whether what we’re experiencing in the teaching environment is incipient VRS or actual VRS. This is a very technical debate that I can’t summarize for you, but you can search PPRUNE for topics on settling with power to see it.
• The FAA curriculum includes a VRS demonstration where recovery is initiated “at the first sign of VRS.” Both the Australian Civil Aviation Safety Authority and Transport Canada stress in their training guides that they are demonstrating incipient VRS in their curriculum, and do not recommend demonstrating actual VRS.