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last gate
compartments are part-filled with various foams or
expanding materials which attenuate blast and serve as a
flame barrier.
blast gate See waste gate.
blast line Chosen radial line from ground zero along
which effects of nuclear explosion (esp. blast effects) are
measured.
blast-off Launch of rocket or air-breathing jet vehicle;
usually, from ground or other planetary surface (colloq.).
blast pad Area immediately to rear of runway threshold
across which jet blast is most severe. Constructed to
surface standards higher than overrun or stopway
beyond.
blast pen Small pen, enclosed by strong embankments
on three sides, but open above, for ground running jet or
rocket aircraft or firing missile engines.
blast pipe see blast tube.
blast tube Refractory tube linking rocket combustion
chamber or propellant charge with nozzle, where these
have to be axially separated.
blast valve Valve in air-conditioning and other systems
of hardened facilities which, upon sensing blast wave,
swiftly shuts to protect against nuclear contamination.
blast wave Shock wave (N-wave) of large amplitude and
followed by significant (4 ata; 40 kPA or more) overpressure.
Travels at or above velocity of sound and causes
severe mechanical damage. Centred on explosions (local
** caused by lightning); attentuation and effective radius
depend on third or fourth power of released energy.
blast-wave accelerator Concept for launching small
payloads into space by accelerating them along an evacuated
tube incorporating a long series of circumferential
shaped charges pointed towards the muzzle.
Blaugas German gas used for airship lift and fuel;
mixture of ethylene, methylene, propylene, butylene,
ethane and hydrogen; literal meaning, blue gas.
BLC Boundary-layer control, especially gross control
of airflow around lifting wing to increase circulation and
prevent flow breakaway.
BLD 1 DSB, double sideband.
2 Berufsverband Luftfahrt-Personal in Deutschland
eV (G).
BLDG, Bldg Building (cloud).
BLE Boundary-layer energiser.
bleed 1 To allow quantity of fluid to escape from closed
system.
2 To extract proportion (usually small) of fluid from
continuously flowing supply; eg compressed air from gasturbine
engine(s).
3 To allow fluid to escape from closed system until
excess pressure has fallen to lower level or equalised with
surroundings.
4 To remove unwanted fluid contaminating system
filled with other fluid, eg * air from hydraulic brakes.
5 To allow speed or height of aircraft to decay to
desired lower level, thus *-off speed before lowering flaps.
6 To allow electronic signal or electrical voltage to
decay to zero (eg, * glide path during flare in automatic
landing).
bleed air Compressed air bled from main engines of gasturbine
aircraft. Uses can include cabin and seal
pressurization, anti-icing and environmental control.
bleed and burn Vertical lift system in which fuel is burned
in a vertical combustion chamber fed with air from main
blind nut
engine (extra airflow may or may not be induced by
ejector effect).
bleeder resistor Resistor permanently coupled across
power supply to allow filter capacitor charge to leak away
after supply is disconnected (see bleed-off relay).
bleeder screw Small screw in tapped hole through
highest point of hydraulic or other liquid system to facilitate
bleeding (4) air or vapour.
bleeding 1 Expulsion of every trace of air or other gas
from an enclosed liquid system.
2 Extraction of bleed air.
bleeding edge Edge of map or chart where cartographic
detail extends to edge of paper.
bleed-off relay In laser, discharges capacitors when
switched off, to render accidental firing impossible.
blended Aerodynamic (arguably, also hydrodynamic)
shape in which major elements merge with no evident line
of demarcation. Thus, aeroplane having * wing/body (see
next two entries).
blended-hull seaplane Marine aeroplane, generally
called in English flying boat, in which planing bottom is
blended into fuselage. Involves dispensing with chine,
sacrificing hydrodynamic behaviour in order to reduce
aerodynamic drag.
blended wing/body Aircraft in which wing/fuselage intersections
are eliminated. Today important for reasons of
stealth.
blend point In aerodynamic shapes having rigid and flexible
surfaces mutually attached (eg Raevam, variable inlet
ducts, flexible Krügers), point in section profile at which
flexibility is assumed to start.
BLEU Blind Landing Experimental Unit (Bedford,
UK).
BLF Breakeven load factor.
BLG 1 Laser-guided bomb (F).
2 Body (-mounted) landing gear.
BLI Belgische Luchtvaart Info.
blimp Non-rigid airship (from ‘Dirigible Type B, limp’,
colloq. until made official USN term in 1939).
blind 1 Without direct human vision.
2 Without external visibility, e.g. in dense cloud.
3 Of radar, incapable of giving clear indication of target
(eg see * speed).
blind bombing Dropping of free-fall ordnance on surface
target unseen by aircrew.
blind bombing zone Restricted area (strictly, volume)
where attacking aircraft know they will encounter no
friendly land, naval or air forces.
blind fastener See blind rivet [though need not have rivetlike
form].
blindfire Weapon system able to operate without visual
acquisition of target.
blind flying Manual flight without external visual cues.
blind-flying panel Formerly, in British aircraft, separate
panel carrying six primary flight instruments: ASI,
horizon, ROC (today VSI), altimeter, DG and TB
(turn/slip).
blind landing 1 Landing of manned aircraft, esp. aerodyne,
with crew deprived of all external visual cues.
2 Landing of RPV unseen by remote pilot except on TV
or other synthetic display.
blind nut Nut inserted or attached on far side of sheet or
other member to which there is no access except through
bolt hole.
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