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download 1 Any load acting downwards, eg on wing at
negative angle of attack.
2 To remove unexpended ordnance or camera magazines
from aircraft after operational sortie or aborted
mission.
downlock Locks landing gear in extended position.
down-look radar Radar capable of detecting targets
close to ground when seen from above.
downrange Away from launch site in direction of target
or impact area.
downselect To select [Pentagonese].
downsize 1 Of manufacturer, to reduce payroll.
2 Of air-carrier, to switch to smaller aircraft.
downspring Long-travel coil spring imparting nearconstant
force on lightplane elevator control which at low
airspeeds makes pilot pull stick back, effect fading as
airspeed rises.
downstage From upper stages of multi-stage vehicle
downwards (signals, vibration, fluid flow, pressure, etc).
downstairs At a lower altitude (UK colloq.).
downstroke In a piston engine, movement of the piston
from top dead centre to bottom dead centre.
downtilt Downward tilt of thrust axis, normally of
single-engine tractor propeller aircraft, to maintain
adequate longitudinal stability, esp. in high-power climb.
downtime Period during which hardware is inoperative
following technical failure or for maintenance.
downward identification light White light on underside
of aircraft for identification, with manual keying for
Morse transmission.
downwash 1 Angle through which fluid stream is
deflected down by aerofoil or other lifting body, measured
in plane parallel to plane of symmetry close behind
trailing edge; directly proportional to lift coefficient.
2 Angle through which fluid stream is deflected by a
propeller, or a rotor of rotary-wing aircraft, measured
parallel to disc.
3 Some authorities consider it not as an angular
measure but as a rate of change of momentum, equal but
opposite to lift. It is increasingly being taken to mean the
induced velocity in the airflow through a propeller, hence
the need for the term * angle, symbol ε.
4 Not least, often taken to mean linear velocity of flow
through helicopter main rotor in hovering flight.
downwind Direction away from source of wind; G/S
= TAS + W/V.
downwind leg Leg of circuit flown downwind, 180° from
landing direction.
downwing side Inner side of aeroplane in banked turn.
DP 1 Direction des Poudres (F).
2 Data (or display) processor.
3 Differential protection.
4 Dual-purpose (in case of artillery, against air and
surface targets).
5 Dew point.
6 Departure, or departure procedure.
7 Deep.
8 Deep penetration.
D p Parasite drag.
dP Differential pressure.
DPA 1 Defence Procurement Agency [of the MoD,
managing 1,000+ projects, Bristol BS34 8JH] (UK).
2 Data Protection Act.
3 Diphenylamine.
DPMAA
4 Digital pressure altimeter.
5 Digital pre-assembly.
6 Defense Production Act (USAF).
DPAC Direction des Programmes Aéronautiques
Civiles (F).
DPAO Defence Public-Affairs Organization [Canberra,
ACT2600] (Australia).
DPB 1 Dual-purpose bomblet, for soft- or hard-skinned
targets.
2 Defence Procurement Board (India).
DPBAC Defence Press and Broadcasting Advisory
Committee (UK).
DPBV Disabled-passenger boarding vehicle.
DPC 1 Defence Planning Committee (NATO).
2 Defence Production Committee (J).
3 Departure control.
4 Digital phase coding.
DPCM Differential, or digital, pulse-code modulation.
DPD Data-processing device.
DPDS Distributed, or digital, processing and display
system (maritime sensors).
DPDT Double-pole, double-throw.
DPDU Data protocol data, or display, unit.
DPE 1 Designated pilot examiner.
2 Department of Public Enterprise [runs Irish civil aviation].
3 Duration of present emergency, the notional period
of service for members of the armed services conscripted
or volunteered in WW2 (UK).
DPEE Directorate of Proof and Experimental
Establishments (UK, MoD formerly).
DPELS Dual-pack Evolved Sea Sparrow launch
system.
DPEM Direct-purchased equipment maintenance.
DPEO Dispersant piston-engine oil.
DPEWS, D-pews Design-to-price electronic-warfare
suite.
DPF Data-processing facility.
DPFG Data-processing functional group.
DP.47 See Silcodyne.
DPG 1 Data-processor, or processing, group.
2 Defense Planning Guidance, policy directive underlying
the budget process (DoD).
DPH Dew-point hygrometer.
DPI Direct petrol-injection.
dpi Dots per inch.
DPICM Dual-purpose improved conventional
munition.
DPKO Department of PeaceKeeping Operations (UN).
DPL 1 Disabled-passenger lift.
2 Dewpoint line.
3 Denied Parties List [with whom no US industrial
supplier is permitted to trade] (US).
4 Diode-pumped laser.
DPLA RPV or UAV (R).
DPLL Digital phase-lock loop.
DPM 1 Digital pulse-modulation.
2 Digital processing module.
3 Digital plotter map.
4 Development program manual.
DPMA Data Processing Management Association
(US).
DPMAA Direction du Personnel Militaire de l’Armée
de l’Air (F).
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