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DEI
4 Of mechanical system, minimum number of independent
generalised co-ordinates required to define positions
of all parts at any instant. Generally, *** equals number
of possible independent generalised displacements.
DEI Development engineering inspection.
de-icing Removal of ice accretion by thermal, mechanical
or chemical means. Note: anti-icing prevents
accretion.
de-icing fluid Glycol/alcohol mixtures are common for
removing frost from parked aircraft. Fluids for use in
flight include ethyl or isopropyl alcohol and ethylene or
propylene glycols.
DEIMS Defense economic-impact modelling system
(DoD).
de-ionisation time Time for gas-discharge tube to return
to neutral condition after interruption of anode current.
deka Prefix, ×10 [non-SI].
del Delete.
DEL Delay, delay message; also DLA (ICAO code).
de Laval nozzle Con-di nozzle used in steam turbines,
certain rockets, and some tunnels.
delay 1 Distance from point directly beneath aircraft to
beginning of area visible to its radar.
2 Electronic delay at start of time base used to select
particular segment of total.
3 Difference in phase between two EM waves of same
frequency.
delayed automatic gain control Applied only to received
signals above predetermined level, so permitting only
weak signals to be fully amplified.
delayed CCIP CCIP for highly retarded bomb.
delayed drop Live parachute descent begun by
prolonged free fall. Controlled by wearer, unlike delayed
opening.
delayed explosive tyre failure Several aircraft have been
destroyed by rupture in flight of an MLG tyre overheated
by heavy or prolonged braking before takeoff.
delayed flap approach Otherwise conventional landing
approach, usually by commercial jet, in which AFCS
(TCC) or FMS is programmed to postpone final configuration
until very late stage, typically near airport
perimeter. Reduces noise and fuel burn.
delayed opening Opening of parachute canopy automatically
delayed by barostat to allow rapid fall through
stratosphere to safer altitude, usually 10,000–15,000 ft,
3050–4570 m.
delayed repeater Comsat which stores messages and
retransmits later, usually at high rate in brief period of
time.
delay indefinite ATC cannot yet estimate duration of
delay; usually followed by Expect further clearance.
delay line Passive network, such as closed loop of
mercury, capable of delaying signal without introducing
distortion.
delay parameter Also called altitude *, time that elapses
between sharp nose-up command and start of climb or
arrest of sink. Significant in large aircraft on landing,
when sudden download at tail has opposite to desired
effect [except canard aircraft].
delay rate Unusual measure of airline punctuality:
number of delays (usually 5 min) per 100 scheduled departures.
delivery error Overall inaccuracy of weapon system
resulting in dispersion of shots about aiming point.
demonstrator programme
delphinopter Class of micro air vehicles weighing c4·5g
combining tail-flapping propulsion with a forward wing
which twists for trajectory control. Most alternate
between flapping and gliding.
Delrin UV-stabilized acetyl-resin adhesives.
DELSC Defence Electrical and Electronic Standardization
Committee.
delta (δ ) 1 Surface deflection angle, thus eδ = elevator
deflection angle.
2 Difference; thus * 1700–1745 is 45 min.
3 Delta wing, or delta-wing aircraft.
Delta Gold Top FAI rating for glider pilot, requiring
flight of 300 km or closed circuit (landing back at start) of
200 km.
delta h, δ h Quantified change in altitude or height above
ground.
delta hinge Helicopter main-rotor flapping hinge, giving
blade freedom to flap up/down vertically. Thus, * is
perpendicular to both blade axis and axis of rotation.
Delta Silver FAI qualification for glider pilot requiring
distance flight 50+ km and [can be same flight] 5+ h
duration.
Delta-3 Helicopter tail rotor with two pairs of blades
not crossing at 90°.
delta-V, δV, V Quantified change in velocity, usually
airspeed.
V whirl Change in whirl velocity, usually across a single
stage of compression or expansion.
delta wing Wing of basically triangular plan-form with
one apex at front and transverse trailing edge, usually with
sharp leading-edge sweep giving low aspect ratio.
deluge pond Facility at site for testing or launching large
vertically mounted rockets into which cooling water is
flushed; also called skimmer basin.
DEM 1 Digital elevation model.
2 Data-exchange model.
3 Detector electronics module.
demand breathing See demand mask.
demand mask Mask through which oxygen or other
therapeutic gas flows only on inspiration of wearer.
demand mode Acars mode initiated by either aircraft or
ground processor.
demand oxygen See demand mask.
demijohn Fluid container of cylindrical form (F).
Demiz Distant early-warning military identification
zone.
demodulation Detection of received signal by extracting
modulating signal from carrier.
Demon Demodulation of noise.
demonstrate 1 To display new hardware according to
detailed test schedule before certificating authority or
sponsoring military customer.
2 More specifically, to show compliance with numerical
performance values, reliability or maintainability.
demonstration flight Made for potential customer [on
board], normally not forming part of an airshow
programme.
demonstration lifejackets Demo jackets are kept in a
special locker, and are not normally considered part of
actual emergency equipment.
demonstrator programme 1 Showing of new civil aircraft
in visits to potential customers.
2 Agreed schedule of tests of new hardware, including
complete aircraft, before military customer in advance of
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