U V W Unanticipated Yaw/Loss of Tail Rotor Effectiveness  (LTE)..........................................................................11-18 Use of Collective........................................................11-13 Venturi effect .................................................................2-4 Vertical Flight ..............................................................2-17 Vertical Takeoff to a Hover ...........................................9-6 VFR Flight into IMC .................................................11-24 Vision in Flight ............................................................12-2 Visual Acuity ...............................................................12-3 Visual Deficiencies ......................................................12-2 Vortex Ring State.........................................................11-9 Vuichard Recovery ....................................................11-10 Weathercock Stability (120-240°) .............................11-20 Weight.........................................................2-3,2-5,6-2,7-2 Weight and Balance Calculations ..................................6-4 Winds .............................................................................7-2  I-4