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horizon
horizon 1 Actual boundary where sky and planetary
body appear to meet: visible *.
2 Apparent boundary as modified by atmospheric
refraction, terrain, fog or other influence: apparent *.
3 Great circle on celestial sphere at all points 90° from
zenith and nadir: celestial *.
4 Line resembling apparent * but above or below:
false *.
5 Locus of points at which direct rays from terrestrial
radio transmitter become tangent to Earth: radio *.
6 Artificial horizon (instrument).
horizon and pitch scale HUD symbology comprising a
horizon line, parallel lines above and below (±2° or 5°) for
pitch information, and heading marks at 5° intervals.
horizon bar Fixed horizontal reference in most types of
horizon (6), HSI and attitude-displays.
horizon sensor Radiometer or other sensitive passive
receiver used to align one axis of spacecraft or satellite
with apparent horizon of Earth or other body; also called
*-seeker.
horizontal Used in Hatol to mean short or vertical
takeoff with fuselage substantially level; used in Hotol to
mean takeoff along runway (CTOL) instead of straight up
in vertical attitude.
horizontal error Error in range, deflection or miss-radius
which weapon system exceeds on half of all occasions
when firing on target on horizontal plane. When trajectory
at arrival is near-vertical ** is CEP; where trajectory
slanting, giving elliptical dispersion, ** is probable error.
horizontally opposed engine Piston engine with left and
right rows of horizontal cylinders and central crankshaft.
horizontal parallax Geocentric parallax of body on
observer’s horizon, = angle subtended at body by Earth
radius at equator.
horizontal plane Usually that through longitudinal [OX]
axis and perpendicular to vertical.
horizontal project One in which hierarchy in
design/project team is minimised and each member works
full-time on single project.
horizontal scanning Scanning in azimuth only at near-0°
elevation; rare (see scanning).
horizontal situation indicator, HSI Standard pilot panel
instrument for all except small GA aircraft; includes Hdg
(T, M), angular deviation from VOR, INS or other track,
Tacan/DME or INS display, and alphanumeric readout
of G/S and possibly other data.
horizontal stabilizer Tailplane.
horizontal tailplane Tailplane.
horizontal technology integration Using common hardware,
such as sensors, scanners/windows, stabilization
and software shared between two or more systems, such
as FLIR, IRST, LST, etc.
Hormoconis resinae By far the most common jet-fuel
fungus.
horn 1 Operating arm of simple manual flight-control
surface to which cable is attached.
2 Microwave aerial coupling waveguide to free air to
give directional pattern; three basic forms are pyramid,
sectoral and biconical, first two having rectilinear funnel
appearance.
3 Acoustic emitter tube whose varying cross-section
and final area control acoustic impedance and directivity.
4 Small area of control surface ahead of hinge axis,
usually at tip, sometimes shielded at low deflection angles
hot
by fixed surface upstream and usually housing massbalance;
when surface deflected provides aerodynamic
force assisting deflection.
horn aerial See horn (2).
horn balance See horn (4).
horn check Verify correct functioning of landing-gear
warning horn.
Hornet Hazardous-ordnance engagement toolkit, to
defeat terrorist SAM (US).
horsal Horizontal ventral fin (originally on XF10F).
horsepower Non-SI unit of power; traditional hp
defined as 550 ft-lb/s = 0.745700 kW; metric * [called ch
or PS] defined as 75 kg-m/s = 0.7355 kW. There is also
electric * defined exactly as 0.746 kW. Brake * is measured
at output shaft by applying known retarding torque; indicated
* calculated from area of indicator diagram and
rpm; frictional * is indicated minus brake *; equivalent *
is turboprop bhp plus addition factored from residual jet
thrust. Aircraft engines also have various * ratings, as do
some nations’ pilot certificates.
horsepower loading See power loading.
horseshoe Revetment having this shape in plan.
horseshoe vortex 1 Combination of finite wing plus
trailing vortex from each tip, forming circulation of
approximate square-cornered U-shape in plan. The flow
above and below the wing can be divided into any number
of local *.
2 Semi-toroidal flow of ground sheet ahead of VTO
hovering in headwind.
Horus Hypersonic orbital return upper stage.
HOS 1 Human operator simulator.
2 Helitow observation system.
hose 1 Flexible conduit for fluid (liquid or gaseous).
2 Verb, to fire long burst of gunfire at or ahead of
hostile or challenged aircraft.
HOSG Helicopter Operations Study Group (UK).
host aircraft That acting as carrier to test installation, or
parent to UAV/drone.
host computer One to which remote terminals or I/O
devices are connected.
hostile Target known or assumed to be enemy, esp. one
seen on remote display.
hostile track One which, based upon established criteria,
is determined to be enemy airborne, ballistic or orbiting
threat.
host nation One whose territory houses infrastructure
forming part of an international system or aircraft of a
friendly air force.
HOT Higher-order term.
Hot High-subsonic, optically tracked, teleguided.
hot 1 Fast-landing (colloq.).
2 With afterburner in operation.
3 With combustion in operation (pressure-jet tip drive
or HTP/hydrocarbon rocket).
4 Strongly contaminated by fallout.
5 Hazardous to vicinity (see * mission).
6 Including propellant ignition (see * test).
7 Ready for firing (launch or static test).
8 High-temperature parts of gas turbine (see * end).
9 Thermally anti-iced, thus * prop.
10 In ground refuelling, with engine(s) running.
11 Currently in use [restricted area].
12 Production line with significant number of items still
to be manufactured.
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