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end allowance
bend allowance Additional linear distance of sheet
material required to form bend of specified radius.
bending brake Workshop power tool for pressing metal
sheet without dies.
bending moment Moment tending to cause bending in
structural member. At any section, algebraic sum of all
moments due to all forces on member about axis in plane
of section through its centroid.
bending relief Design of aircraft to alleviate aeroelastic
deflection, especially of main wing (eg, by distributing
mass of fuel and engines across span).
bending stress Secondary stresses (eg, in wing skins and
spar booms) which resist deflection due to applied
bending moments.
bends Acute and potentially dangerous or lethal
discomfort caused by release of gases within a mammalian
body exposed to greatly reduced ambient pressure. Thus,
a hazard of high-altitude fliers and deep-sea divers (see
aeroembolism, decompression sickness).
bent 1 Feature of many gun mechanisms, engaging in
cocked position with sear.
2 Signal code indicating that facility is inoperative
(DoD).
3 Transverse frame capable of offering vertical support
and transmitting bending moment.
4 Damaged in an accident (colloq.).
bent beam, bent course Radio or radar beams significantly
diverted from desired rectilinear path by
topographic effects, hostile ECM or other cause.
benzene Liquid hydrocarbon, C 6 H 6, s.g. 0.899, with
characteristic ring structure forming base of large number
of derivatives. Used as fuel or fuel additive, as solvent in
paints and varnishes, and for many other manufactures.
benzine Mixture of hydrocarbons of paraffin series,
unrelated to benzene. Volatile cleaning fluid and solvent.
benzol Benzene C 6 H 6 .
BEP Back-end processor; MS adds management
system.
BER 1 Beyond economic repair.
2 Bit error rate, also b.e.r.
BERD Business enterprise research and development.
Berline Single-engined transport aircraft (F).
Bermuda triangle Region at base of stiffener bonded to
composite sheet subject to high stress.
Bernoulli’s theorem Statement of conservation of energy
in fluid flow. Basis for major part of classical aerodynamics,
and can be expressed in several ways. One form
states an incompressible, inviscid fluid in steady motion
must always and at all points have uniform total energy
per unit mass, this energy being made up of kinetic energy,
potential energy and (in compressible fluid) pressure
energy. Making assumptions regarding proportionality
between pressure and density, and ignoring gravity and
frictional effects, it follows that in any small parcel of fluid
or along a streamline, sum of static and dynamic pressure
is constant, expressed as p ½ ρV 2 = k. Thus, if fluid
flows subsonically through a venturi, pressure is lowest at
throat; likewise, pressure is reduced in accelerated flow
across a wing.
BERP, Berp British experimental helicopter main rotor
programme.
Berp rotor RAE 9648 profile inboard, 9645 outboard,
broad tip 9634.
BERR Business enterprise and regulatory reform.
bezel
Berry Amendment Prohibits use of appropriated funds
to purchase items [e.g. speciality metals] unless they are
certified as US products.
beryllium Hard, light, strong and corrosion-resistant
white metal, m.p. about 1,278°C, density about 1.8.
Expensive, but increasingly used for aerospace structures,
especially heat sinks and shields.
BES Best estimate.
b.e.s. Best-endurance speed.
bespoke software Designed for a specific application.
best-climb speed Usually V IMD .
best-economy altitude Narrow band of altitudes where
specific range is maximum.
best-endurance speed Always V IMD .
best-fit parabola Profile of practical parabolic aerial
capable of being repeatedly manufactured by chosen
method. In many cases *** is made up of numerous flat
elements.
best-range speed V IMR ; speed at which tangent to curve
of speed/drag is a minimum; hence where speed/drag is a
maximum and fuel consumption/speed a minimum.
BET Best estimate of trajectory.
BETA, Beta Battlefield exploitation and target
acquisition.
beta 1 Sideslip (β).
2 Angle of sideslip.
beta-dot, β .
First-order derivative used to model delay in
rate of change of sidewash at vertical tail.
beta-1, β1 Yaw pointing angle (zero sideslip).
beta-2, β2 Lateral translation (constant yaw angle).
Bet-AB Rocket-accelerated free-fall deep-penetration
bomb (USSR, R).
beta blackout Communications interference due to beta
radiation.
beta control Control mode for normally automatic
propeller in which pilot exercises direct command of pitch
for braking and ground manoeuvring. Also called beta
mode.
beta lines, β-lines Arbitrary lines drawn roughly parallel
to compressor surge line to assist off-design performance
calculations.
beta mode See Beta control.
beta particle Elementary particle emitted from nucleus
during radioactive decay, having unit electrical charge
and mass 1/1,837th that of proton. With positive charge,
called positron; with negative, electron. Biologically
dangerous but stopped by metal foil.
beta strips Low-intensity strip lights on skin of military
aircraft to assist close formation flying at night.
beta target The trapezoid on a PFD.
beta vane Transducer measuring yaw (sideslip) angle.
BETT, Bett Bolt extrusion thrust-terminator.
bev Billion electron volts. No longer proper term; 10 9 ev
is correctly 1 Gev.
bevel gear Gearwheel having teeth whose straight-line
elements lie along conical surface (pitch cone); thus, such
gears transmit drive between shafts whose axes intersect.
bevelled control Flight-control surface whose chordivise
taper in thickness is increased close to the trailing edge.
BEVS Boom [for air-refuelling] enhanced visual system.
BEW Bare engine weight.
BEXR Beacon extractor and recorder.
bezel Sloping part-conical ring that retains glass of
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