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double drift
double drift Method of determining wind velocity by
observing drift on three true headings flown in specific
pattern.
double-end feed Cooling air fed under pressure to both
inner and outer radii of a turbine nozzle guide vane, to
emerge through [possibly hundreds of] surface holes.
double engine Power unit containing two engines driving
co-axial propellers; usually one half can be shut down for
cruising flight.
double-entry compressor Centrifugal or radial-flow
compressor that takes in fluid on both sides of impeller.
double farval Aerobatic routine by section of four in
diamond with 1 (box) and 4 (lead) inverted with respect to
2 and 3; thus at times it would be 2 and 3 that were
inverted, 1 and 4 then being upright.
double-flow engine Usually, bypass turbojet or
turbofan.
double-fluxe Bypass or turbofan engine (F).
double-headed Warship having SAM systems both fore
and aft of central superstructure.
double-hinged rudder Rudder with additional hinge near
mid-chord for maximum effectiveness at low speeds with
large camber and total angle.
double horn Dangerous ice accretion on LE forming two
LEs, with channel between them.
double lift Winchman and rescuee together.
double manned Two crews per aircraft.
double modulation Carrier wave of one frequency is first
modulated by signal wave and then made to modulate
second carrier wave of another frequency.
double notch Flight-control system giving reduced
surface movement for given input.
double propulsion Use of two independent sources of
thrust, one for lift and the other for propulsion, in an aerodyne.
Historical examples include Rotodyne and Mirage
III-V.
double-protection honeycomb Honeycomb structure
protected by chemical surface conversion process and
then varnish dip.
doubler Additional layer of sheet or strip to reinforce
structural joint.
double-root blade Rotating blade or vane with root
fitting at each end to enable it to be fitted into disc either
way.
double-row aircraft Cargo airlifter able to carry unit
loads (military vehicles, pallets, etc) side-by-side.
double-row engine See twin-row.
double sideband AM signal with carrier removed [still
needs some bandwidth].
double slot Passive-suction system in upper surface of
wing of high-subsonic aircraft in which air is continuously
extracted immediately downstream of shockwave (to
stabilize and weaken it) and discharged immediately
upstream of it. Improves C L and buffet boundary.
double-slotted flap Flap with vane and thus two slots,
one between wing and vane, and the second between vane
and flap.
double-T Tail comprising a vertical surface above each
of two booms joined at top by a horizontal.
doublet 1 In fluid mechanics, source and sink of equal
strength whose distance apart is zero.
2 Violent uncommanded stop-to-stop rudder movement.
downlink data
3 Any precisely timed commanded pulse of ± n o , usually
on the elevator.
doublet antenna Antenna (aerial) composed of two
similar elements in line but separated and fed in centre,
and having total length equal to half wavelength; half a
dipole.
double taper Taper of aerofoil which incorporates
change in angle at part-span.
Double Tumble Aerobatic manoeuvre comprising 720°
rotation in pitch about the transverse axis, AOA alternately
positive and negative.
double-wedge aerofoil Section suitable for straight
supersonic wings and blades of supersonic axial compressors,
characterised by sharp wedge-like taper and sharp
leading and trailing edges.
double wing See Junkers.
doughnut 1 Common shape for plasma contained in
toroidal bottle.
2 Low-pressure tyre on small wheel for soft airfields.
3 Figurative representation of a thermal, in which
central upflow can rise no further and turns over into
surrounding downflow.
Douglas protractor Transparent square covered with
precise rectilinear grid and degrees around the edge.
Douglas scale Table of numerical values of sea state
[nine, from calm to confused] as one axis and swell [again
nine] as the other.
DOV 1 Data over voice.
2 Discrete operational vehicle (low-profile, does not
appear to be military or para-military), usually nonflying.
Dovap Doppler velocity and position.
Dover control Patented linkage permitting all engines of
multi-engine aircraft to vary power in unison or with any
desired differences [obs.].
DOW Dry operating weight.
Dowgard Aviation ethylene glycol (Dow Chemicals).
down Faulty and unusable.
downburst Local but potentially dangerous highvelocity
downward movement of air mass, eg when
arrested by sea-breeze front; chief cause of windshear.
down-conversion To lower EM frequency-band.
downcutting Milling so that teeth enter upper surface of
workpiece.
downdraft Bulk downward movement of air such as
commonly found on lee side of mountain or caused by
descending body of cool air.
downdraft carburettor One in which air is taken in at top
and travels downwards; reduced fire hazard, and less risk
of foreign-object ingestion.
downed aircraft Aircraft that has made forced landing
or ditching, esp. because of battle damage.
Downey cycle A standard product life cycle, used by the
British MoD.
down-45 line Straight sustained dive at inclination of
45°.
downgrade To reduce security classification of a document
or item of classified material.
downlink Radio transmission from air- or spacecraft to
Earth.
downlink data Transmissions to Earth from spacecraft
giving such information as astronaut respiration or cabin
temperature; computers alert flight controllers to any
deviation (7).
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