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unstable aircraft
unstable aircraft General meaning is one which, when
diverted [even slightly] from straight/level flight, will
diverge in uncontrolled manner.
unstart Explosively violent breakdown of correct (ie
started) airflow through supersonic inlet to airbreathing
engine, notably with expulsion of shockwave(s) and
temporary reversal of flow. All highly supersonic (M3+)
engines have such a large contraction ratio and
constricted throat that any yaw, spillage from
neighbouring engine, gunfire or other disturbance can
cause *.
UNSTBL Unstable air mass.
UNSTDY Unsteady.
unstick Point at which fixed-wing aerodyne leaves
surface of land or water; hence * run = ground or water
run; * speed = that at which aircraft becomes airborne,
usually about 25% of way from V R to V 2 symbol V us .
unstick-speed ratio V/V us , ratio of aircraft speed to unstick
speed either as % or as fraction. Usually plotted as
abscissa on takeoff performance graph, esp. of marine
aircraft.
unstressed Not bearing significant external load.
unsupported site Possible operating site for V/STOL
aircraft but devoid of prestocked supplies, eg POL,
ammunition etc.
Unsvc Ground facility is unserviceable.
unsymmetrical Generalized chemical description of
molecular structure where left is not mirror image of right;
eg in 1, 2 dimethylhydrazine each N has an H and a CH 3
attached (symmetrical), but 1, 1 dimethylhydrazine has
left N joined to two H atoms and right N joined to two
CH 3 methyl molecules and is unsymmetrical (UDMH).
unsymmetric flight Condition in which aircraft (aeroplane
or glider) is not balanced about longitudinal axis,
due to roll, roll/yaw or other rotary manoeuvre causing
gross alteration to normally symmetric wing lift. Hence
unsymmetric load, that in unsymmetric flight.
unsymmetric thrust Thrust with one failed engine away
from centreline; normally called asymmetric.
UNT Undergraduate navigator training (S adds system)
(USAF).
UNTSO UN Truce Supervisory Organization.
unusable fuel Fuel that cannot be used in flight with
wings level and at cruise AOA (or nose 3° up). Trapped
fuel is that fuel remaining in worst case on ground using
booster pumps for defuelling and switching off immediately
associated LP warning lights illuminate. See
Unpumpable fuel.
UNUSBL Unusable.
unwarned exposed Friendly troops are in open when
NW detonates on near enemy.
UOC Underwing ordnance capacity.
UOES User operational evaluation system.
U-174 Standard headset jack plug (US, NATO).
UOR Urgent Operational Requirement (UK).
UOS UCAV operational system.
UP 1 Unrotated projectile (1938–1944 name for British
rockets, virtually all air/ground).
2 Unguided projectile.
3 Unruly passenger.
4 Unknown precipitation.
5 Universal platform.
U p Helicopter rotor-blade out-of-plane velocity normal
to plane of disk.
upper baseplate
UPA Union of Professional Airmen [affiliated ALPA,
office Washington, DC] (USA).
up and away 1 Descriptive of all powered-lift systems
capable of giving VTO.
2 The operative mode giving VTO, as distinct from
(e.g.) STOVL.
uparmour To improve armour protection.
UPB Unruly passenger behaviour, also called air rage.
UPC Unit production cost.
UPCF Union des Pilotes Civils de France.
up-chaff Normally, between chaff cloud or stream and
target; hence * interception, with good radar view of
target.
up-conversion Move to a higher EM frequency band.
update To refresh memory, radar picture or other electronic
device with later information; hence * rate, rate
(possibly as often as kHz) at which a system or input is
scanned for new or changed values.
UPDFTS Updraughts.
updraught carburettor One fed by duct conveying air
upwards from below; in US updraft carbureter.
UPDTS Updates.
Uped UV pre-initiation electrical discharge (laser).
up-45 line Straight sustained climb at inclination of 45°.
up-front control Single small panel in fighter cockpit
giving complete control of all CNI functions.
up gear US voice command or check for raising landing
gear.
upgrade To rebook passenger into higher class.
UPI Undercarriage position indicator (UK).
Upkeep Water-skipping dambusting bomb (UK, 16–17
May, 1943).
upkeep Generalized US term for all tasks aimed at
preventing deterioration of hardware, eg GA aircraft; less
used for commercial and military.
UPL AOPA (Luxembourg).
uplift 1 Total disposable load of cargo aircraft, or cargo
taken on board.
2 Fuel taken on board, esp. away from home base.
3 Fuel taken aboard from air-refuelling tanker
aircraft.
uplink 1 Telemetry, command, data or other electronic
link between Earth and spacecraft.
2 Com. link from ground to aircraft, especially telephone
call to passenger.
upload Load acting vertically upwards, or vertical
component of loads, eg airloads due to lift.
uplock Mechanical lock securing device, eg landing
gear, in up or housed position.
UPM 1 Universal processor module.
2 Ultra-portable multiplexer.
upper air Portion of atmosphere above lower troposphere,
normally (eg for synoptic purposes) that above
pressure height 850 mb. Hence, * chart. See next three
entries.
upper-air observation Observation of upper air, above
effective range of surface measures; also called sounding.
upper airspace Normally all FLs above 250
(7,620 m/25,000 ft).
upper atmosphere Not strict term, normally interpreted
as above tropopause, but also as above 30 km or 20 miles.
upper baseplate Triangular or hexagonal frame on
which cabin of flight simulator is mounted.
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