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reversal 1 Half a cycle of oscillating applied load, ie
from maximum load in one direction to maximum load in
opposite direction.
2 Control reversal (see reversed controls).
3 Difference in direction exceeding 90° between surface
wind and that in upper air.
reversal parameter Sign (±) of partial derivative of pitchloop
bandwidth to pilot’s pitch control gain, considered
in design of carrier aircraft.
reversal speed Lowest EAS at which control reversal is
manifest.
reversal temperature That at which characteristic spectral
lines of incandescent gas disappear against
black-body spectrum.
reversal zone Zone within ILS glideslope or course
sector in which slope of sector characteristic curve is
negative.
reverse bias That which reduces current.
reverse blindness Obscuration of flight-deck vision by
snow or other material in reverse-thrust mode.
reverse breakdown voltage That at which reverse current
across p/n junction increases rapidly with little increase in
reverse voltage.
reversed bootstrap ECS in which the ram-cooled air
passes through an air-cycle turbine before returning
through the heat exchanger and compressor.
reversed controls Flight-control axis about which, in
particular severe conditions, application of pilot input
demand causes aircraft response in opposite sense,
normally due to aeroelastic distortion of structure. Usual
axis is roll, where under very high EAS (ideally not within
limits of flight manual) large aileron deflection causes
opposite twist of wing which more than neutralizes rolling
moment due to aileron; in effect aileron acts as tab and
wing as aileron.
reverse dihedral Destabilizing rolling moment in sideslip
at high AOA when slipstream increases lift of leeward
(trailing) wing. Also called negative dihedral.
reversed lobsterback A Phase II combustor heat shield
[Rolls-Royce, superseded by Phase-V].
reversed rolling moment That due to reversed control in
rolling plane; also called roll reversal.
reverse engineering Process of studying a finished
product [precise geometry, materials and surface finish] so
that it can be copied. Classic case is Tupolev’s * of B-29
to create Tu-4.
reverse-flow combustor One in which air enters at front,
travels to rear-mounted fuel burners and then returns as
hot gas within flame tube to leave radially inward from
front; also called folded combustor, return-flow.
reverse-flow engine Gas turbine incorporating axial
compressor which draws in air around rear end and
compresses it in forwards direction, before turning flow
radially outwards (often by added centrifugal stage) to
flow back to rear through combustor(s).
reverse-flow region 1 Quasi-circular region near hub of
helicopter main rotor disc, on retreating side, within
which relative airflow is from trailing to leading edge, ie
helicopter airspeed is greater than blade speed due to
rotation.
2 Any region in turbulent boundary layer in which
there is a majority-flow reversal.
reverse idle Power-lever setting at which engine is at idle
(usually flight-idle because prior to touchdown on
revetment
committed landing) with reverser buckets in reversethrust
mode.
reverse launch In direction opposing Earth’s rotation.
reverse localizer Back course.
reversement See reverse turn.
reverse origami Unfolding of spacecraft, or its aerial[s].
reverse pitch Special ground-only setting available on
some propellers and ducted propulsors, including several
variable-pitch turbofans, in which blades accelerate air
forwards, creating retrothrust proportional to engine
power without change in direction of rotation.
reverser Device for deflecting some or all of efflux from
jet engine to give reverse thrust (retrothrust); can take
form of pivoting clamshell buckets, blocker doors and
peripheral cascades, or other forms, and may include
turbofan core or fan exit only. Angle through which jet is
turned seldom exceeds 135°.
reverse sweep Forward sweep.
reverse thrust Operating mode for jet engine equipped
with reverser, obtainable only by overcoming gate or
detent which may be locked until weight is on oleos for
specified period, eg 1.5 s; normally obtained by moving
power levers past idle down to ** mode, further movement
in this direction opening throttle to full power to give
maximum retrothrust.
reverse torque Any situation in which the driven
member [e.g., propeller] drives the prime mover. Could be
dangerous, as in a Viscount which was dived at high IAS
when one propeller ran away fully fine.
reverse turn Opposite of Immelmann: half-roll followed
by half loop. Also called reversement.
reverse-velocity rotor Main lifting rotor of compound or
hybrid helicopter which behaves as an aeroplane in
cruising flight, with a large portion in high-speed reversed
relative airflow.
reversible propeller One in which reverse pitch may be
selected.
reversing layer Thin lower part of Sun’s atmosphere;
cooler than photosphere and source of Fraunhofer lines.
reversion Change of operating mode (eg, but not exclusively,
of flight-control system from normal powered to a
degraded or manual mode).
reversionary Available following failure of primary
system.
reversionary facility Facility for changing operating
mode, either automatically or upon human command,
esp. one following failure or degradation of existing
channel or subsystem.
reversionary lane Back-up or standby channel.
reversionary mode Normally means advanced integrated
flight system is available for pilot input of selected
navigation mode from choice of several unrelated
systems, eg INS, local R-Nav, Doppler, VOR/DME or
Omega.
reverted rubber Rubber heated beyond critical point at
which it loses basic mechanical properties, esp. elasticity,
and becomes sticky and permanently deformable. In one
of the three aquaplaning modes, lack of anti-skid system
causes locked wheel(s), reverted rubber in contact with
runway covered in standing water, rapid steam generation
and aquaplaning on steam layer above water.
revetment Area protected on three sides by blastresistant
wall of concrete, sandbags, compacted earth or
other material, either to protect occupants and parked
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