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dispersion error
7 Measure of resolving power of spectroscope or
spectrograph, usually expressed in A/mm.
8 Tendency over long period of commercial traffic to
move from primary to secondary airports.
9 Scatter of actual touchdown points on runway over a
period.
dispersion error Distance from aim point to mean point
of impacts.
dispersion hardening Scattering of fine particles of
different phase within metallic material, resulting in
overall strengthening.
dispersion pattern Distribution of series of rounds fired
from one weapon or group of weapons on fixed aim under
conditions as nearly identical as possible.
dispersion warhead Discharging bomblets, FAE or other
multiple or dispersed payloads.
displaced threshold Threshold not at downwind end of
full-strength runway pavement. It is usually beyond it,
and is available for takeoff or for end of landing roll, but
not for touchdown.
displacement 1 In air interception, separation between
target and interceptor tracks to provide interceptor acquisition
space.
2 Distance from standard point (usually origin)
measured in given direction.
3 Of IC engine, total volume swept by pistons during
crankshaft rotation from BDC to TDC. Also known as
swept volume.
4 Of airship or balloon, mass of air displaced by gas,
expressed as weight or volume.
5 Lateral, vertical or angular * of any point of zero
DDM from localizer or glidepath.
displacement thickness Dimension characteristic of all
boundary layers and equal to thickness of completely
stagnant fluid having same overall effect. Equal to
distance through which each streamline is displaced from
position it would have assumed had fluid been inviscid.
∝ u 3vl
δ∗ = ∫ 0 ( l –– ) dy ♎ –––
V V
where u is local boundary layer velocity, V free-stream
velocity, y distance from solid surface, ν kinematic
viscosity and 1 characteristic length; actual boundarylayer
thickness is nearly three times δ*.
display Graphic presentation of data for human study.
Display Authorisation Document required from
national aviation authority before pilot can take part in
airshow.
display datum Also called display centre, the mid-point
of the crowd-line.
disposable lift Gross lift less fixed weight of an aerostat.
disposable load Maximum ramp weight minus OEW.
DISR 1 Descent imager [and] spectral radiometer.
2 Department of Industry, Science and Resources
(Australia).
disreef system Timing system for automatically
releasing reef of parachute.
disrupter-type spoiler Maximises local turbulence.
disruptive threat Pentagonese for a totally unpredicted
threat that ‘comes out of left field’ to tilt the balance of
power (DoD).
dissimilar air-combat training Mock air combat with
friendly fighters of different type(s) acting part of enemy
distributor
aircraft, chosen for performance similar to that of enemy
types and usually painted to resemble them.
dissimilar redundancy Use of different teams of engineers
and programmers to design and code the software
in different channels or control lanes in an attempt to
avoid sudden multiple failure.
dissipation trail Rift in clouds caused by passage of [jet]
aircraft. Abb. distrail.
Dist Distance or district (ICAO).
distance Standard airline unit is nm (contrary to SI); up
to 1,200 nm airline * calculated as D (great-circle
distance) + (7 + 0.015D); above 1,200 nm measure is
D + 0.02D.
distance bar Rigid bar linking tow vehicle with aircraft.
distance marker 1 Numbers painted on runway side to
indicate thousands of feet to upwind end.
2 Reference marker on radar display; usually one of
series of concentric circles. Also known as range marker.
distance-measuring equipment Airborne secondary
radar sending out paired pulses (interrogation) received at
ground transponder; time for round trip is translated into
distance. DME offers 252 frequencies from 962 to
1,213 MHz at 1 MHz spacing, providing 126 channels
each comprising two frequencies 63MHz apart.
Distant Marshal At gliding championship, official
charged with arranging tugs and gliders in correct start
sequence.
distillate 1 Any petroleum product.
2 Fuel oil, eg for diesels.
distortion 1 Undesired change in shape.
2 Undesired change in waveform.
3 In radio or sound reproduction, failure exactly to
transmit or reproduce received waveform.
4 Variation of flow velocity or temperature across
transverse plane through gas turbine.
distraction ECM mode in which hostile missile locks-on
to decoy before it can see real target.
Distress & Diversion ATC cells [or in UK RAF units]
which maintain 24-h monitor on v.h.f./u.h.f. emergency
frequencies to offer assistance.
distress frequency Internationally 121.5 kHz.
distress signal Signal transmitted by vehicle in imminent
danger.
distributed-aperture system EO sensors providing a
protective sphere around aircraft for missile warning,
navigation support and night operations.
distributed data-processing Distribution of EDP (1)
capability among a number of positions in a geographically
large system.
distributed jet system Any arrangement in which a
power source is arranged to augment lift along the length
of an aerofoil, examples being the jet flap, augmentor
wing, EBF, IBF, CCW and USB.
distributed load One which has no single point of application
but is distributed over a line or area, such as air load
on a surface.
distributed mass-balance One distributed along span of
control surface.
distributed mission training Creating realistic battlespace
for aircrew by using networked simulators.
distributor 1 Rotary switch feeding HT in sequence to
spark plugs.
2 Circumferential gallery connecting engine fuel manifold[s]
to burner nozzles, probably incorporating a *
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