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U
U 1 Overall heat-transfer coefficient.
2 Linear acceleration (archaic usage).
3 Internal or intrinsic energy.
4 Aircraft has 4096-code transponder with altitude
encoding.
5 With appropriate suffix, flow velocity component
[along orthogonal axes, radial or tangential], or vehicle
speed, eg U o .
6 Designation prefix, aircraft, unpiloted (USN
1946–55), RAF (from 1956), or utility (USAF from 1952),
USN (from 1955).
7 Modified mission, prefix and suffix, utility (USN).
8 Designation first letter, missile, underwaterlaunched
(DoD).
9 Designation second letter, missile, attack on underwater
target (DoD).
10 Airfield is unlicensed.
11 Upravlayemaya, = guided (R).
12 Umrüst, = factory modification (G, WW2); -B or
Bausatz added conversion kit.
13 Upper (wing or flight level).
14 Identity unknown.
15 Until.
16 Unicom.
17 Uranium.
18 Aircraft category UAV (FAI).
19 Unidirectional [runway].
20 Other meanings include unmanned, unwatched,
unverified, upward and user-fee.
u 1 Force in structural member due to unit load; also
[quite different] uniform load per unit length or area.
2 Tangential velocity, or linear velocity of point in
rotating structure, e.g. compressor rotor blade or aeroplane
in roll.
3 Also used for translational velocities.
4 Surface unpaved.
5 Unit of atomic mass.
6 Specific internal energy.
7 Velocity along X [body] axis, alternative to U(5).
8 Subscript, upper surface.
(U) 243.0 Hz available on request.
U-alpha Free-stream fluid velocity, usually written Uα.
U-code See U (4).
U-index Monthly mean of differences between consecutive
daily mean values of horizontal component of
Earth’s magnetic field.
u-index Value of U-index divided by sine of magnetic
co-latitude multiplied by cos of angle between magnetic
meridian and horizontal component.
U-joint Universal joint.
U-tail Aeroplane tail with twin verticals attached to
fuselage (can be inclined outwards but not applicable to
butterfly tail).
U-235 Fissile uranium, isotope typically 0.71 per cent of
natural metal, nearly all the rest being U-238.
UA 1 Uncontrolled airspace.
2 Unit of account; standard accounting unit (EEC).
3 Until advised.
4 Airep, upper-air pirep.
5 Unnumbered acknowledgement.
6 Unit of Action (USA).
7 Unmanned aircraft.
UAA 1 Up and away (JSF).
2 University Aviation Association [office, Cahokia
IL] (US).
3 Upper advisory area.
4 Unusual aerial activity (CAA, UK).
UAAA Ultralight Aircraft Association of Australia.
UAB Until advised by (ICAO).
UAC 1 Upper-air computer, or center (FAA).
2 Upper-airspace control (CAA).
3 Upper-area control centre.
4 Universal avionics computer.
UACC See UAC 3.
UACCV Unit of action command and control vehicle.
UACO Unamnned autonomous collaborative operations
(USA, USAF).
UA/cS Unmanned aircraft system. including
supporting infrastructure.
UAD 1 Unidirectional aligned discontinuous.
2 Upper advisory (route).
UADA Upper advisory area.
UADE Ultralightweight aerial diesel engine [usually
Ulade].
UAI Union Astronomique Internationale [office, Paris]
(Int.).
UAJ Unattended jammer.
UAL 1 Unidirectional approach light[ing].
2 Unit authorization list.
Uα See U-alpha.
UALV Unmanned airlift vehicle.
UAM Underwater-to-air (missile).
UANC Upper-airspace navigation chart.
U&L Upper and lower (wings).
UAOS Unmanned aerial, or aeronautical, observation
system.
UAP Unidentified aerial phenomena.
UAPP Unified adapative planning (or preplanning)
program.
UAR 1 Upper air route.
2 Unattended radar.
UARS 1 Unattended radar station.
2 Unmanned air reconnaissance system.
3 Upper-atmosphere research satellite [NASA,
1991–2001].
UART Universal asynchronous receiver/transmitter.
UAS 1 University Air Squadron(s). (UK).
2 Upper airspace service.
3 Unamnned, or uninhabited, air, or aerial, system.
4 User aircraft system.
5 User application software.
6 Ulster Aviation Society [1968–; Newtonabbey BT36
6PE] (UK).
7 Unassigned (Telabs).
8 Unavailable service (Sprint).
9 Urea ammonimum sulphate.
UASA
UASO
Upper-airspace service area.
Unmanned Air Systems Office (FAA).
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