This decreases the lift the wing produces at the tip to improve the stall characteristics of the wing. Also called washout. 

Two-stroke engine. A simple form of reciprocating engine that completes its operating cycle in two strokes of its piston, one down and one up. Two-stroke-cycle engines are inefficient in their use of fuel, but their simplicity makes them popular for powering light-sport aircraft and ultralight vehicles where light weight and low cost are paramount. 

Ultralight.  A single person only vehicle as defined by 14 CFR section 103.1. 

Uncontrolled airspace. Class G airspace that has not been designated as Class A, B, C, D, or E. It is airspace in which air traffic control has no authority or responsibility to control air traffic; however, pilots should remember there are VFR minimums which apply to this airspace. 

Unicom. A nongovernment air/ground radio communication station which may provide airport information at public use airports where there is no tower or automated flight service station. 

Unusable fuel.  Fuel that cannot be consumed by the engine. This fuel is considered part of the empty weight of the aircraft. 

Useful load.  The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only. 

Unstabilized approach.  The final approach of an aircraft that has not achieved a stable rate of descent or controlled flight track by a predetermined altitude, usually 500 feet AGL. 

Unusual attitude.  An unintentional, unanticipated, or extreme aircraft attitude. 

Useful load. The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only. 

User-defined waypoints. Waypoint location and other data which may be input by the user, this is the only GPS database information that may be altered (edited) by the user. 

Upwind Leg. A flight path parallel to the landing runway in the direction of landing. 

Vapor lock.  A problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporise due to being heated by the engine, by the local climate, or due to a lower boiling point at high altitude. 

VASI. See visual approach slope indicator. 

Vehicle.  Manmade 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 configuration status. 

Vertical axis (yaw). An imaginary line passing 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 instrument 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 instruments. 

VFR. See visual flight rules. 

VFR Terminal Area Charts . Charts designated to depict Class B airspace in greater detail and greater scale than sectional charts. 

