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hybrid RAT
hybrid RAT Ram-air turbine driving both electric generator
and hydraulic pump.
hybrid rocket One using both liquid and solid propellants
simultaneously; usual arrangement is solid fuel and
liquid oxidant.
hybrid solar array Part folding, part flexible.
hybrid trajectory Any space trajectory intermediate
between that for minimum energy or minimum time and
alternatives offering greater payloads, longer launch
windows or other advantages.
hybrid wave EM wave in waveguide having both
magnetic and electric components in plane of propagation.
Hycatrol One of several trade names (FPT Industries)
for rubber/metal bonded structures.
Hycorder Hyperspectral covered-lantern optical recognition
device recorder.
hyd Hydraulic[s].
Hydim Hydraulic interface module.
hydrant dispenser Installation under apron or
finger/gate area stand for refuelling aircraft without need
for tanker vehicles.
hydrant pit Below-ground compartment, normally
covered, housing connections and controls for fuel,
hydraulic, lube oil or other liquid supply.
hydraulic catapult Catapult.
hydraulic fluid See hydraulics.
hydraulicing Abnormal resistance to movement of
machine, esp. piston engine, caused by hydraulic lock in
lower cylinders part-full of essentially incompressible oil;
can cause serious damage.
hydraulic lock Use, frequently inadvertent, of essentially
incompressible liquid to prevent movement of
mechanical part.
hydraulic motor Source of mechanical power, usually
rotary, driven hydraulically.
hydraulic power unit Source of power to energize
hydraulic system, eg when main engines inoperative.
hydraulic RAT Ram-air turbine driving hydraulic
pump.
hydraulics Science of liquids either in motion (hydrodynamics)
or as media for transmitting forces
(hydrostatics). In aerospace generally science of nearly
incompressible liquids enclosed in closed-circuit pipe
systems at high pressure and used both to apply forces,
with little fluid motion, and supply power, with large fluid
motion. Media originally mineral oils, today also engine
fuel, phosphate esters, cholorinated silicones, silicate
esters and (supersonic and missiles) alkyl silicate esters.
There are several so-called synthetic ester-based fluids,
but most aircraft still use mineral oils, notably DTD.585
[UK], MIL-H-5606 [US], H.515 [NATO], AMG-10
[Russia] and AIR.320 [France].
hydraulic seal Total seal between two annular spaces in
engine formed by ring-fins or flanges projecting into ring
of oil created by centrifugal force.
hydraulic starting Used in small [eg, missile and UAV]
jet engines: external supply feeds pressure to hydraulic
motor; once engine is started, motor functions as
hydraulic pump.
hydraulic system Complete aircraft installation
comprising closed circuits of piping, engine-driven
pumps, accumulators, valves, heat exchangers, filters and,
usually, emergency input such as RAT or MEPU;
normally divided into at least two systems with maximum
degree of independence. Each system is assigned task of
driving selected items by linear actuators, motors or other
output devices.
hydrazine Family of chemicals, mostly colourless
liquids, often corrosive; basic member is *, (NH 2 ) 2 ;
common rocket fuel is unsymmetrical dimethyl *,
NH 2 N(CH 3 ) 2 ; another is monomethyl *, NH 2 HH.CH 3 .
hydrobooster Hydraulic power unit used in boosted (not
fully powered) flight-control system (colloq.).
hydrocarbon Compound of hydrogen and oxygen only;
some millions are known, including all derivatives of
petroleum, which in product form often have other
elements added for specific purposes. Many aviation fuels
are alkanes (paraffins), which are open chains with carbon
atoms having single-valence bonds; first six members,
with one to six carbon atoms respectively, are methane,
ethane, propane, butane, pentane and hexane. These are
prefixed n (normal), distinguished from prefix iso of more
reactive branched alkanes. Alkenes have one carbon with
double bond, based on ethylene (CH 2 ) 2 . Aromatic * series
are based on hexagon ring of benzene C 6 H 6 with three
double bonds.
hydrodynamics Science of fluid motion, esp. of water.
hydroflap Water rudder on flying boat.
hydrofoil Lifting surface operating in water. As well as
being vehicles in their own right, surface-piercing and
ladder * have been used on marine aircraft.
hydroforming Shaping parts by fluid pressure, esp. of
thin-foil items.
hydrogen Symbol H, least-dense element, comprising
88 per cent of atoms in Universe, LH 2 (liquid *) has
density 77.0 gl –1 , 4.806 lb/ft 3 at 13.8K (the triple point) and
70.8 gl –1 at BPt of 20.28K, –253°C, where it becomes GH 2
(gaseous *) with density 0.0008988 (0.08988 gl –1 ) or
0.005611 lb/ft 3 ; isotopes are bivalent deuterium, trivalent
tritium. In air at STP 10 3 cu ft [28.317 m 3 ] of * will lift
32.090 kg (70.746 lb).
hydrogenation Causing to combine with hydrogen, esp.
at high pressure and in presence of catalyst such as nickel
or platinum, in conversion of crude petroleum distillates
into tailored fuels and other products. * of coal also
important to future aviation.
hydrogen bomb So-called H-bomb, or thermonuclear
weapon TN or TNW; comprises NW surrounded by
lithium deuteride (LiD, the lithium being isotope Li-6)
and a little tritium T. Triggering the NW emits neutrons
which instantly convert the Li-6 into H+He-3+T. The He-
3 and T then combine with remaining D to form more He
and more neutrons, which also convert the U-238 bomb
case into Pu-239, causing an additional (fission) reaction.
hydrogen bus Airport airside buses are among the first
vehicles to be powered by hydrogen, usually GH 2 stored
on vehicle roof.
hydrogen economy Hypothetical future in which Earth’s
limited reserves of petroleum are replaced by gaseous and
liquid hydrogen. No new technology is needed, but see
next.
hydrogen fusion Essentially limitless power could be
unlocked if mankind could emulate the Sun and build a
facility which continuously converted hydrogen into
helium. Conversion would yield 630,000,000,000J of
energy per gram.
hydroglider Glider with marine alighting gear.
hydroglider
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