Glossary — D

Dacron Artificial fabric for light aircraft covering; trade name.

DADC Digital air data computer.

DADS Digital air data system.

DARPA Defense Advanced Research Projects Agency (US) (briefly ARPA before February 1996).

DAS Defensive Aids Suite.

databus Electronic highway for passing digital data between aircraft sensors and system processors, usually MIL-STD-1553B or ARINC 419 (one-way) and 619 (two-way) systems.

dB Decibel.

DC Direct Current.

DECU Digital engine (or electronic) control unit.

dem/val Demonstration/validation.

derated Engine restricted to power less than potential maximum (usually such engine is flat rated, which see).

design weight Different authorities have different definitions; weight chosen as typical of mission but usually much less than MTOW.

DF Direction-finder, or direction-finding.

DGAC Direction Generale a l'Aviation Civile. French certification authority.

DHI Daewoo Heavy Industries (South Korea).

dihedral Upward slope of wing from root (or intermediate point) to tip.

disposable load Sum of masses that can be loaded or unloaded, including payload, crew, removable equipment, usable fuel and other consumables; MTOW minus OWE.

DLIR Downward-Looking Infra-Red.

DME UHF distance-measuring equipment gives slant distance to a beacon; DME element of Tacan.

DoD Department of Defense.

dog-tooth A sharp discontinuity in the leadin-edge of a wing or tail surface resulting from an increase in chord (see also sawtooth).

Doppler Short for Doppler radar - radar using fact that received frequency is a function of relative velocity between transmitter or reflecting surface and receiver; used for measuring speed over ground or for detecting aircraft or moving vehicles against static ground or sea.

double-slotted flap One having an auxiliary aerofoil ahead of main surface to increase maximum lift.