Glossary   U - Z

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

Vg diagram   A chart that relates velocity to load factor It is valid only for a specific weight, configuration and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds

VNE   See never-exceed speed

VNO   See maximum structural cruising speed

VS   See stalling speed

VX   See best angle-of-climb speed

VY   See best rate-of-climb speed

Victor airways   Airways based on a centerline that extends from one VOR or VORTAC navigation aid or intersection, to another navigation aid (or through several navigation aids or intersections); used to establish a known route for en route procedures between terminal areas

Visual approach slope indicator (VASI)   A visual aid of lights arranged to provide descent guidance information during the approach to the runway A pilot on the correct glideslope will see red lights over white lights

Visual flight rules (VFR)   Rules in the Code of Federal Regulations that govern the procedures for conducting flight under visual conditions

Visual meteorological conditions (VMC)   Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling meeting or exceeding the minimums specified for VFR

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

Warm front   The boundary area formed when a warm air mass contacts and flows over a colder air mass Warm fronts cause low ceilings and rain

Warning area   An area containing hazards to any aircraft not participating in the activities being conducted in the area Warning areas may contain intensive military training, gunnery exercises, or special weapons testing

Waypoint   A designated geographical location used for route definition or progress-reporting purposes and is defined in terms of latitude/longitude coordinates

Washout   The design of the WSC wing in which a wing is twisted so its angle of attack is less at the tip than at the root Washout decreases the lift the wing produces at the tip to improve the stall characteristics of the wing Also called twist

Washout strut   The structural member attached to the leading edges which holds the tip twist for the wing at low or negative angles of attack

WCA   See wind correction angle

Weather briefing   Means for pilots to gather information vital to the nature of the flight from a flight service station specialist

Weathervane   The tendency to point into the wind

Weight   A measure of the heaviness of an object One of the four main forces acting on an aircraft The force by which a body is attracted downward 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

Weight-Shift Control Aircraft   Powered 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 flexibly deform rather than the use of control surfaces

Whip stall   A pitch attitude that is too high for a WSC, at which the tips would stall from flying outside the WSC limitations or flying in extreme/severe turbulence

Wind correction angle   Correction applied to the course to establish a heading so that track will coincide with course Also called the Crab angle

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 Also called the wind correction angle or crab angle

Wind shear   A sudden, drastic shift in wind speed, direction, or both that may occur in the horizontal or vertical plane

Wing   A fabric skin with an aluminum frame that produces the lift necessary to support the WSC in flight; including the flight wires/control frame below and the ground wires/king post above

Wing keel   The WSC structural component in the longitudinal center of the wing that connects the two leading edges together at the nose and connects the carriage to the wing

Wing loading   The amount of weight that a wing must support to provide lift

Wingspan   The maximum distance from wingtip to wingtip

Wing twist   A design feature of the WSC that reduces the angle of attack from the root to the tip

Wingtip vortices   The rapidly rotating air that spills over an aircraft’s wings during flight The intensity of the turbulence depends on the aircraft’s weight, speed, and configuration It is also referred to as wake turbulence Vortices from heavy aircraft may be extremely hazardous to small aircraft

World Aeronautical Charts (WAC)   A standard series of aeronautical charts covering land areas of the world at a size and scale convenient for navigation (1:1,000,000) by moderate speed aircraft Topographic information includes cities and towns, principal roads, railroads, distinctive landmarks, drainage, and relief Aeronautical information includes visual and radio aids to navigation, airports, airways, restricted areas, obstructions and other pertinent data

WSC   See weight-shift control

Weight-Shift Control—Land (WSCL)   WSC that takes off and lands on land This can be wheels or ski equipped

Control—Sea (WSCS)   WSC that takes of the water This can be pontoons or a boat configuration

Yaw   Rotation about the vertical axis of an aircraft

Zulu time   A term used in aviation for Coordinated Universal Time (UTC) which places the entire world on one time standard

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