FH.XI.D.K1

From the FAA library

• Helicopter Flying Handbookp. 11-9
  Chapter 11: Helicopter Emergencies and Hazards › Vortex Ring State

  helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in circulating the air in a doughnut pattern ... result, the airflow of the inner blade sections is upward relative to the disk. This produces a secondary vortex ring in addition to the normal tip vortices. The secondary vortex ring is generated about the point on the blade where…

• Helicopter Flying Handbookp. 11-20
  Chapter 11: Helicopter Emergencies and Hazards › System Malfunctions › Tail Rotor Vortex Ring State (210–330°)

  imperative to maintain positive control of the yaw rate and devote full attention to flying the helicopter. Tail Rotor Vortex Ring State (210–330°) Winds within this region cause a tail rotor vortex ring state to develop. [Figure ... result is a nonuniform, unsteady flow into the tail rotor. The vortex ring state causes tail rotor thrust variations, which result in yaw deviations. The net effect of the unsteady flow is an oscillation of tail rotor thrust. Rapid…

• Aviation Maintenance Technician Handbook - Powerplantp. 1-13
  Chapter 1: Aircraft Engines › Piston Rings › Oil Control Rings

  Compression Ring The purpose of the compression rings is to prevent the escape of combustion gases past the piston during engine operation. They are placed in the ring grooves immediately below the piston head. The number of compression rings used ... each piston is determined by the type of engine and its design, although most aircraft engines use two compression rings plus one or more oil control rings. The cross-section of the ring is either rectangular or wedge shaped with…