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lade element
Royce, * is unshrouded and not separated from fan by
stators, otherwise similar in principle to TF39 of 1966.
blade element Infinitely thin slice (ie having no spanwise
magnitude) through blade (1) in plane parallel to axis of
rotation and perpendicular to line joining centroid of slice
to that axis. Thus, blade is made up of infinity of such
elements from root to tip, usually all having different
section profile and blade angle. *momentum theory deals
with the rotor of a hovering helicopter.
blade face Surface of blade (1) corresponding to underside
of a wing. With propellers, called thrust face.
blade inspection method Spars of helicopter main-rotor
blades are pressurized, loss of pressure warning of crack
(Sikorsky).
blade loading Of helicopter or autogyro, gross weight
divided by total area of all lifting blades (not disc area).
blade loading coefficient Helicopter rotor thrust coefficient
divided by solidity, C r σ.
blade passing noise Component of internally generated
noise of turbomachinery, caused by interaction between
rotating blades and wakes from inlet guide vanes and
stationary blades. Generates distinct tones at bladepassing
frequencies, which in turn are product of number
of blades per row and rotational speed.
blade root 1 Loosely, inner end of blade (1).
2 Where applicable, extreme inboard end of blade
incorporating means of attachment (see blade shank).
Blades Battlespace laser detection system (AEFB/
AFRL).
blades! Verbal call to pull piston engine through specified
number of propeller blades before start.
blade section Shape of blade element.
blade shank Where applicable, portion of blade of nonaerofoil
form extending from root to inboard end of
effective aerofoil section. Unlike root, * of propeller is
outside spinner.
blade span axis 1 Axis, defined by geometry of root
pitch-change bearings, about which blade is feathered.
2 Axis through centroids of sections at root and tip.
blade station Radial location of blade element,
expressed as decimal fraction of tip radius (rarely, as
linear distance from axis of rotation, from root or from
some other reference).
blade sweep Deviation of locus of centroids of all
elements of blade from radial axis tangential to that locus
at centre. Was marked in early aircraft propellers, usually
towards trailing edge (ie, trailing sweep); leading sweep,
in which tips would be azimuthally ahead of hub, is rare.
blade tilt Deviation of locus of centroids of all elements
of blade from plane of rotation. Again a feature of early
aircraft propellers, more common form being backward
tilt, visible in side view as propeller flat at back and
tapered from boss to tip in front.
blade tip grinding Precise grinding of the tips of an
assembled axial compressor rotor. In some engines the
final trim is by allowing the tips to rub inside the casing.
blade twist 1 Unwanted variation in pitch from root to
tip caused by aerodynamic loads.
2 Natural twist which reduces blade angle from root
to tip.
blade/vortex interaction Between each helicopter mainrotor
blade and the vortex created by its predecessor, a
principal cause of slap.
blade width ratio Ratio of mean chord to diameter.
BlastGard
BLAGF British Light Aviation and Gliding
Foundation (London W8).
BLAM Barrel-launched adaptive munition(s).
blank 1 Workpiece sheared, cut, routed or punched
from flat sheet before further shaping.
2 Action of cutting part from flat sheet, esp. by using
blanking press and shaped die.
3 Round of gun ammunition without projectile.
4 All-weather cover tailored to engine inlet or other
aperture, forming part of AGE for each aircraft type.
blanket 1 Layer of thermally insulating material
tailored to protect particular item, typically refractory
fibre housed in thin dimpled stainless steel. Term is not
normally used for noise insulation.
2 Layer of heating material supplied with electrical or
other energy.
blanket cover Fabric cover for aircraft machine-sewn
into large sheet, draped over structure, pulled to shape
and sewn by hand.
blanketing 1 Supression, distortion or other gross interference
of wanted radio signal by unwanted one.
2 In long-range radio communication, prevention of
reflection from F layers by ionisation of E layer.
blanketing frequency Signal frequency below which
radio signals are blanketed (2).
blank-gore parachute Parachute having one gore left
blank, without fabric.
blanking 1 Using press and blanking die to cut blanks
(1).
2 In electron tube or CRT, including TV picture tubes,
suppression of picture signal on fly-back to make return
trace invisible.
blanking cap Removable cap fitted to seal open ends of
unused pipe connections or other apertures in fluid
system.
blanking plate Removable plate fitted to seal aperture in
sheet, such as unused place for instrument in panel.
blanking signal Regular pulsed signal which effects
blanking (2) and combines with picture signal to form
blanked picture signal. Sometimes called blanking pulse.
blanks See blank 4, blanking plate.
Blasius flow Theoretically perfect laminar flow.
blast 1 Loosely, mechanical effects caused by blast
wave, high-velocity jet or other very rapidly moving fluid.
2 Rapidly expanding products from explosion
and subsequent blast wave(s) transmitted through
atmosphere.
blast area Region around launch pad which, before final
countdown of large vehicle, is cleared of unnecessary
personnel and objects.
blast cooling In rotating electrical machines and other
devices, removal of waste heat by airflow supplied under
pressure.
blast deflector Structure on launch pad or captive test
stand to turn rocket or jet engine efflux away from ground
with minimal erosion and disturbance.
blast fence Large barrier constructed of multiple
horizontal strips of curved section, concave side upwards,
which diverts efflux behind parked jet aircraft upwards
and thus reduces annoyance and danger at airfields.
blast/fragmentation Warhead, common on AAMs and
SAMs, whose effect combines blast of HE charge and
penetration of fragments of rod(s) or casing.
BlastGard Proprietary honeycomb materials in which
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