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direct frontal
need to rotate to different attitude; eg lateral force by
combined rudder and chin fin, vertical by tailerons/flaps/
spoilers or vectored thrust.
direct frontal Air-combat tactic for double attack in
which one interceptor closes head-on on each side of
enemy force.
direct injection Precise metered doses of fuel sprayed
directly into cylinder combustion space, not into eye of
supercharger.
direction See azimuth, bearing, course, heading, track.
directional aerial, antenna Aerial which radiates or
receives more efficiently in one direction than in others.
directional beacon Transmitter emitting coded signals
automatically to enable aircraft to determine their bearing
from the beacon with a communications receiver.
directional gyro Free-gyro instrument for indicating
azimuth direction. Usually free from turning errors but
prone to precess/wander.
directional instability Tendency to depart from straight
flight by a combination of sideslipping and yawing.
directional marker Ground marker indicating true north
and direction and names of nearest towns.
directional network waveform A high-speed net linking
mobile stations throughout a theater of operations.
directional solidification Casting metal alloys in such a
way that all transverse grain boundaries are eliminated,
leaving long columnar crystals aligned with direction of
principal stress.
directional stability Tendency of an aircraft to return at
once to its original direction of flight from a yawing or
sideslipping condition; also known as weathercock
stability.
direction-finder Automatic or manually operated
airborne receiver designed to indicate bearing of
continuous-wave ground radio beacon (see ADF).
direction indicator See directional gyro.
directivity Antenna radiant energy per unit solid angle
in a given direction [usually main axis] divided by that
averaged over all directions.
direct lift control Use of aerodynamic surfaces, esp.
symmetric spoilers, to provide instantaneous control of
rate of descent without need to rotate aircraft in pitch.
direct operating cost Costs of operating transport
aircraft, usually expressed in pence or cents per seat-mile,
per US ton-mile or per mile, and including crew costs, fuel
and oil, insurance, maintenance and depreciation.
Excluding indirect expenses, such as station costs or
advertising; usually taken as 100 per cent of direct costs.
director 1 Aircraft equipped to control RPV or missile.
2 In air traffic control, a radar controller.
3 Fire-control tower in warships.
director horizon One name for a panel instrument
combining an artificial horizon with radio inputs,
especially ILS and VOR.
direct shadow photo Simplest and oldest shadow
photography: bright point source of light (in former days,
spark) throws shadow of body and shockwaves on to
photographic plate.
direct side-force control DFC (2) flight-control system in
which aircraft (heavier than air) can be translated sideways
without yaw or change of heading by application of
direct lateral force.
direct transit Special rules under which aircraft may
pause [eg, to refuel] in a Contracting state.
disc loading
direct-view storage tube CRT storage tube needing no
visor in bright sunshine.
direct-vision optics See next.
direct-vision panel Flight-deck window or part of
window that can be opened.
direct voice input Control of function [eg. panel display,
weapon selection, radio channel] by spoken command.
dirigible Capable of being guided or steered; thus an
airship but not a balloon.
Dir/Intc Direct intercept.
DIRP 1 Defense industrial reserve plant (US).
2 Defense Industrial Research Program (Canada).
DIRS 1 Damage information reporting system.
2 Distributed IR system.
dirty 1 Aircraft configuration in which aerodynamic
cleanness is spoilt by extension of drag-producing parts,
eg landing gear, flaps, spoilers, airbrakes.
2 NW whose detonation releases large quantity of toxic
radiological material or emissions.
dirty bird Stealth aircraft coated [especially freshly] with
ferrite paint.
dirty duty On intercept-ready status (USAF aircrew).
DIS 1 Distributed-intelligence system (MMI).
2 Defense Investigative Service (US DoD).
3 Defence Intelligence Service (UK MoD).
4 Distributed interactive simulation.
5 Data-intensive system[s].
6 Drawing-introduction schedule.
7 Defence Industrial Strategy [December 2005–] (UK).
DISA Defense Information Systems Agency (US).
disabled aircraft Damaged, or otherwise unairworthy,
aircraft which could interfere with an airfield’s operation.
DISC Defence Intelligence and Security Centre
(Chicksands, UK).
Disc 1 Disconnect.
2 Direct [defense injection, reception and emergency
action message command and control terminal] improvement
and sustainment contract (NMCC).
disc 1 Ring on which one stage of compressor blades
is carried. There is no defined boundary between this
and a ring.
2 Hub carrying blades of fan or turbine.
3 Circular area swept by propeller or lifting rotor.
disc area Of propeller or helicopter rotor, area of circle
described by tips of blades.
Disch Discharge.
dischargeable weight 1 All masses which may be jettisoned
overboard in emergency.
2 Of airship, total weight that can be consumed or jettisoned
and still leave ship in safe condition with specified
reserves of fuel, oil, ballast and provisions.
discharge coefficient The ratio of actual to theoretical
mass flows, symbol C d .
discharge correction factor Of rocket nozzle, ratio of
mass flow to that of ideal nozzle which expands identical
working fluid from the same initial conditions to same exit
pressure.
discharge valve Manually operated and opened sparingly
to release hot air from balloon envelope. Generally
= dump valve (3).
discing Operation of propeller in ground fine pitch to
cause aerodynamic drag.
disc loading Helicopter weight, or rotor thrust, divided
by main-rotor disc area, T/A.
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