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utterfly
maximum continuous power”, normally to effect interception.
butterfly Distorted figure-8 pattern, looking like a
butterfly, flown by orbiting combat aircraft on weaponguidance,
EW or, rarely, AWACS duty.
butterfly tail Comprises two oblique (dihedral in region
25°–45°) fixed stabilizer surfaces each carrying a hinged
surface, the latter operating in unison as elevators or in
opposition as rudders; also called V tail.
butterfly valve Fluid-flow valve in form of pivoted plate,
usually having circular form to close a pipe.
butt joint Sheet joint with edge-to-edge contact without
overlap, with jointing strip along either or both sides.
buttock lines Profiles of intersection of longtitudinal
vertical planes with surface of solid bodies, esp. aircraft
fuselages and marine floats. Zero ** is that on axis of
symmetry. Used in lofting, these lines do not necessarily
correspond with structural members.
button Extreme downwind end of usable runway
(colloq.).
button contact Electrical connector in which a plunger is
pressed against the surface of a convex disc [button]; this
ensures clean separation, e.g. on launch of a missile.
buttonhead rivet Rivet with approximately hemispherical
head; used where tensile load may be high.
butt rib Compression rib at joint between outer and
inner wing, or wing and fuselage.
butts Facility for testing aircraft guns [rare, singular].
BUV Backscatter ultraviolet.
BuWeps Bureau of Weapons, combined BuAer and
BuOrd in 1959 (USN).
Buys Ballot’s law Professor Buys Ballot postulated that
an observer with back to wind in N hemisphere has lower
pressure to left (in S hemisphere, to right). True for any
isobar pattern.
buy the farm To be killed in a crash, not excluding military
action (colloq.).
buzz 1 Oscillation of skin or other structure at frequency
high enough to sound as a note.
2 Oscillation of control surface at high frequency.
3 Loosely, any single-direction-of-freedom vibration at
audible frequency.
4 Wake-interaction noise generated by turbomachinery,
esp. large fans, at 900–4,000 Hz.
5 High-frequency, often violent, pulsation of airflow at
supersonic air-breathing engine inlet.
6 To fly aircraft, esp. one of high performance and
manoeuvrability, in way designed to harass another
aircraft or ground target. Transitive, thus “to * the control
tower”.
7 Collective noun for micros.
buzz liner Sound-absorbent liner to fan duct or other
surface bounding wake-interaction noise.
buzz number Extra-large individual aircraft number
(can be unit number or aircraft serial), readable from a
distance.
buzz-saw noise Buzz (3) from shock system of fan with
supersonic flow over blades, composed of discrete tones
at multiples of N 1 .
BV 1 Bureau Veritas.
2 Bleed valve.
3 Boost vehicle.
4 Present visibility.
BVA Bleed-valve actuator.
bypass turbojet
BVCU Bleed-valve control unit.
BVD Battlespace visualization display.
BVI Blade/vortex interaction (helicopter).
BVID Barely visible impact damage.
BVIS Baggage vector interface server, provides routing
system for host systems of all carriers at one airport.
BVOR/BVortac Weather broadcast VOR or Vortac.
BVQI Bureau Veritas Quality International.
BVR 1 Beyond visual range.
2 Best-value rate.
BVTRU Bleed-valve transient reset unit (controls BVs
during transients).
BVU On-board computer (R).
b w Wing span [alternative to b].
BW 1 Biological warfare [or weapons].
2 Bomb (or bombardment). Wing (USAAC, USAAF,
USAF).
3 Bandwidth; also B/W.
BWA Blast-wave accelerator.
BWAN, B-Wan Back-up WAN.
BWB 1 Blended wing/body.
2 Bundesamt für Wehrtechnik und Beschaffung [MoD
procurement office] (G).
BWC Biological and Toxin Weapons Convention,
1972.
BWEA British Wind Energy Association [a major
programme is to evaluate impact of wind farms on
radars].
BWEC Bristol and West of England Consortium [academia,
industry, Government] (UK).
BWER Bounded, or boundary of weak echo region [of
thunderstorms].
BWFT Ministry of research and technology (G).
BWO Backward-wave oscillator.
BWPA British Women Pilots’ Association [1955–;
office, Weybridge KT13 0QN] (UK).
BWRA British Welding Research Association.
BX Base Exchange, today AAFES.
BXA Bureau of Export Administration (US).
BY Blowing spray.
BYD Beyond.
BY$ Base-year dollars.
BYG Blue/yellow/green.
Bygrave Slide rule for solving vector triangles, esp. from
sextant readings (obs.).
bypass 1 Capacitor connected in shunt to provide lowimpedance
alternative path.
2 Alternative flow path for fluid system.
bypass duct Annular space surrounding engine core
through which bypass air flows; in modern turbofans
usually called fan duct. May be short, or extended back to
a mixer.
bypass engine Air-breathing jet engine in which air
admitted at inlet may take either of two flow paths (see
bypass turbojet).
bypass ratio In bypass turbojet or turbofan, numerical
ratio of mass flow in bypass duct divided by that through
core, ie cold jet divided by hot. Some have defined as total
mass flow divided by core mass flow; this is incorrect, and
would always yield numbers greater than 1. BPR is
normally measured at TO power at S/L.
bypass turbojet Turbojet in which mass flow through
LP compressor stages is slightly greater than that
through HP stages, excess being discharged along bypass
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