ULTRALIGHT—A vehicle as defined by 14 CFR  103.1. UNSTABILIZED APPROACH—The final approach  of an aircraft that has not achieved a stable rate of  descent or controlled flight track by a pre-deter- mined altitude, usually 500 feet AGL. UPWIND LEG—A flight path parallel to the landing  runway in the direction of landing.  VEHICLE—Man-made means of transportation; an  ultralight aircraft (not a light-sport aircraft). VENTURI—A specially shaped restriction in a tube  designed to speed up the flow of fluid passing  through in accordance with Bernoulli’s principle.  Venturis are used in carburetors and in many types  of fluid control devices to produce a pressure  drop proportional to the speed of the fluid passing  through them. VENTURI EFFECT—The effect of Bernoulli’s  principle, which states that the pressure of a fluid  decreases as it is speeded up without losing or  gaining any energy from the outside. VERIFIED—Confirmation of information or con- figuration status. VERTICAL AXIS (YAW)—An imaginary line pass- ing vertically through the center of gravity of an  aircraft. The vertical axis is called the z-axis or the  yaw axis. VERTICAL SPEED INDICATOR (VSI)—An in- strument that uses static pressure to display a rate  of climb or descent in feet per minute. The VSI  can also sometimes be called a vertical velocity  indicator (VVI). VERTIGO—A type of spatial disorientation caused  by the physical senses sending conflicting signals  to the brain. Vertigo is especially hazardous when  flying under conditions of poor visibility and may  cause pilot incapacitation, but may be minimized  by confidence in the indication of the flight instru- ments. VFR—See VISUAL FLIGHT RULES. VFR TERMINAL AREA CHARTS—Charts desig- nated to depict Class B airspace in greater detail  and greater scale than sectional charts. VISUAL FLIGHT RULES (VFR)—Code of Federal  Regulations that govern the procedures for con- ducting flight under visual conditions. V LINES—See RISERS. VSI—See VERTICAL SPEED INDICATOR. WAKE TURBULENCE—Wingtip vortices that are  created when an aircraft generates lift. When an  aircraft generates lift, air spills over the wingtips  from the high pressure areas below the wings  to the low pressure areas above them. This flow  causes rapidly rotating whirlpools of air called  wingtip vortices or wake turbulence. WASHOUT—A condition in aircraft rigging in  which a wing is twisted so its angle of incidence is  less at the tip than at the root. Washout decreases  the lift the wing produces to improve the stall  characteristics of the wing. WEATHER BRIEFING—Means for pilots to gather  all information vital to the nature of the flight.  Most often obtained from FSS specialist. WEATHERVANE—The tendency to point into the  wind. WEIGHT—A measure of the heaviness of an object.  The force by which a body is attracted toward the  center of the Earth (or another celestial body) by  gravity. Weight is equal to the mass of the body  times the local value of gravitational acceleration.  One of the four main forces acting on an aircraft.  Equivalent to the actual weight of the aircraft. It  acts downward through the aircraft’s center of  gravity toward the center of the Earth. Weight op- poses lift. WEIGHT-SHIFT CONTROL AIRCRAFT—Pow- ered aircraft with a framed pivoting wing and a  fuselage controllable only in pitch and roll by the  pilot’s ability to change the aircraft’s center of  gravity with respect to the wing. Flight control of  the aircraft depends on the wing’s ability to flex- ibly deform rather than the use of control surfaces. WIND CORRECTION ANGLE—Correction ap- plied to the course to establish a heading so that  track will coincide with course. WIND DIRECTION INDICATORS—Indicators  that include a wind sock, wind tee, or tetrahedron.  Visual reference will determine wind direction and  runway in use. WIND DRIFT CORRECTION—Correction applied  to the heading of the aircraft necessary to keep the  aircraft tracking over a desired track. WIND SHEAR—A sudden, drastic shift in wind- speed, direction, or both that may occur in the  horizontal or vertical plane. WING—A ram-air inflated and pressurized fabric  airfoil that produces the lift necessary to support  the powered parachute in flight; including the lines  that attach to the cart. Also called a parachute,  chute, or airfoil. WING LOADING—The amount of weight that a  wing must support to provide lift. WINGSPAN—The maximum distance from wingtip  to wingtip. G-11