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head-down
2 Cutter and positioning system in most machine tools,
esp. those in which workpiece is stationary.
3 Loosely, downwind end of runway.
head-down Looking into cockpit as distinct from outside
aircraft.
head-down display See HDD.
header tank Inserted at highest point of coolant circuit
of liquid-cooled piston engine, receiving hot coolant from
engine and passing it to radiator[s].
heading Angle between horizontal reference datum and
longitudinal axis of aircraft expressed as three-figure
group 000°-360°; in UK also called course. Datum can be
compass north, magnetic north or true north. Not to
be confused with track [one dictionary actually calls * ‘the
direction of an aircraft path’, precisely what it is not].
heading alignment cone Imaginary cone of 18,000-ft
upper diameter serving to guide Orbiter or STA(6) to
runway.
heading hold Flight-control mode which maintains
selected heading.
heading-orientated map One held in hand so that
heading is towards top of sheet.
heading select Flight-control mode in which aircraft
automatically turns to and holds any inserted *.
head-level display Immediately below HUD.
head moment Total turning moment transmitted
through head(1) in helicopter manoeuvre.
head-on Flying directly towards other aircraft on reciprocal
track.
head resistance Drag.
heads down Control of RPV or UAV without having it
in view.
headset Receive/transmit interface with radio communications
or other system (eg aural warning or missile
launch tone), either worn separately or built into helmet.
Normally includes earpieces or earshells, noise-cancelling
microphone on boom and binaural cable.
heads up 1 Airborne intercept code: “Hostile force,
whole or in part, got through defences” or “I am not in
position to engage” (DoD).
2 Occasionally used to mean head-up [only one human
head can use a HUD at any one time].
head-up display See HUD.
health Generally everyday meaning but applied to hardware;
thus * monitoring, can be equated with inspection,
AIDS output etc.
HEAO High-energy astronomical observatory.
heap cloud Cloud with pronounced vertical development,
e.g., cumulus family.
Heart Health evaluation and risk tabulation.
heart-cut distillate Particular family of kerosene fuels, in
particular JP-6.
HEAT 1 High-enthalpy ablation test.
2 High-explosive anti-tank, shaped-charge warhead.
3 Helicopter electric-actuation technology.
4 High-energy advanced trainer.
Heat Armament panel switch selection for IR AAMs.
heat Measure of atomic/molecular kinetic energy, but
not to be confused with temperature. Symbol Q, unit
joule, J = 0.238846 cal IT .
heat barrier Supposed barrier to increasing flight Mach
number due to kinetic heating.
heat capacity 1 Of a solid [usually metal] object, its mass
multiplied by the specific heat of the material. See next.
heavy alloy
2 Quality of high-power lasers which permits sustained
firing followed by brief cooling period.
heat-engine Prime mover in which energy is extracted
from thermodynamic system in which gas passes through
cycle from which closed PV or T-entropy diagram can be
plotted. Perfect ** has reversible (Carnot) cycle; all
practical ** have lower-efficiency irreversible cycle.
Nearly all aviation ** are constant-pressure gas turbines
or Otto-cycle piston engine.
heater Afterburner (colloq.).
heat-exchanger Radiator in which two fluids are
brought into close contact (eg, cold air and hot oil) so that
one can reject heat to other.
heat flow rate Synonymous with power. SI unit is watt,
W = 3.41214 Btu/h = 0.85985 kcal/h; Btu/h = 0.293071 W.
heat load Rate of heat transfer, = heat flow rate.
heat of ablation Measure of value of ablating material,
rate of heat input divided by rate of mass loss.
heat pipe Contains fluid which is alternately evaporated
and condensed, transferring heat [in spacecraft, to space].
heat pulse Total heat to be absorbed, dissipated, radiated
or otherwise transferred from original kinetic energy
of body on re-entry.
heat-seeker Sensitive IR detector and homing guidance
system.
heat shield Usually non-structural layer protecting
primary structure from high-temperature environment
which would degrade strength, such as around aeroplane
afterburners, at base of large rocket vehicle and, esp., over
upstream face of body on re-entry (later is invariably
ablative).
heat sink 1 Any location to which heat may be removed
from thermodynamic system.
2 Specifically, mass of metal, fuel, oil or other material
which can accept unwanted heat.
heat treatment Heating metals above specific temperatures
followed by slow or rapid cooling to improve
mechanical properties (see carburising, case hardening,
nitriding, precipitation **, solution **).
heave 1 Vertical movement without rotation (simulator).
2 Motion of taxiing aircraft [esp. marine] in vertical
plane, fuselage [hull] remaining level.
heavier than air Having density much greater than that
of air, thus aerostatic buoyancy ignored in calculating lift,
which is assumed generated wholly by aerodynamic or
propulsive forces; aerodyne.
Heaviside layer D, E, F, and F 1 , layers in upper atmosphere
(ionosphere) where UV solar radiation ionises gas
molecules, allowing conduction of electricity.
heavy 1 Flight control; difficult to move.
2 Maintenance, major and prolonged.
3 Warning to ATC of wake turbulence, aircraft MTO
300,000 lb (136,080 kg).
4 US [becoming universal] civil radio traffic, any large
transport, esp. large jet.
5 AA gun, >40-mm calibre (WW2); also, of course, can
mean intense fire from many guns of all calibres.
6 Propeller aircraft, 5,700 kg [12,566 lb] MTOW.
7 Air in balloon envelope close to density of local
atmosphere.
8 Large firefighting tanker, as distinct from Seat.
heavy alloy One tailored to have exceptionally high
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