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leapfrog
leapfrog To delay one ranging pulse train from radar to
avoid two targets being superimposed.
LEAPP Land environment air-picture provision.
learner cost Extra element of direct-labour cost when
work is unfamiliar.
learning curve Fundamental curve portraying fall in
manufacturing time or cost with increasing familiarity;
abscissa is number of aircraft completed (often log scale)
and ordinate is total direct labour cost, or total manufacturing
man-hours or total manufacturing cost
including raw materials and bought-out parts; usually an
idealised curve not allowing for inflation.
Leasat Leased satellite, or space bus hired out for
different payloads.
leasing Possession without title.
least material condition That in which the quantity of
material in a part is minimised, e.g. maximum allowable
hole diameter.
Lecos Light (ie optical) electronic control system.
LEC Locally employed civilian.
LECP 1 Life-extension and capabilities program (US
and ARRC).
2 Low-energy charged particle.
LED 1 Light-emitting diode; - RHA adds recordinghead
assembly.
2 Leading-edge down (surface angular movement).
3 Leading-edge device(s).
4 Low endoatmospheric defence [I adds interceptor].
LEDDM LED (1) dot matrix.
LEED Low-energy electron diffraction.
lee wave See rotor cloud.
LEF 1 Leading-edge flap.
2 Light-emitting film.
left-hand circuit Rectilinear circuit (1) with turns to left,
anti-clockwise seen from above. Almost universal.
left-hand rotation Anti-clockwise, viewed from rear.
left/right needle Needle pivoted at top or bottom of
panel instrument giving steering indication; pilot steers to
keep needle vertical.
left seat That of captain of aircraft; thus, ** time.
left-seater Pilot in command, usually.
leg 1 Main strut of landing gear.
2 Part of flight at constant heading between two
waypoints.
3 Beam of radio range station, identified by particular
flight as inbound * or outbound *.
4 The two parts of a control cable running over a pulley
at each end.
legacy carrier US term for a long-established airline.
legacy systems 1 Those which a nation cannot afford to
replace.
2 In general, those we use today, as distinct from the
much better ones we can envisage. In the course of time
everything becomes a *.
3 Specifically, the previous version.
legend 1 Any fixed printed or electronic warning notice
in cockpit.
2 Explanatory written matter on engineering drawing.
leg restraint Strong belt automatically tightened round
occupant’s legs as ejection seat fires.
Lehar Long-endurance high-altitude rotorcraft (USA).
LEI Lean Enterprise Institute (US).
Leigh light Powerful searchlight [RAF ASW aircraft
1941–45].
let-down
LEIP Leading-edge image process (auto map displays).
Lelfas Long-endurance low-frequency active surveillance
(ASW).
LEM 1 Lunar excursion module.
2 Lean-enterprise model.
3 Linear electric motor.
4 Linear[ised] equations of motion.
Lemac Leading edge of mean aerodynamic chord.
LEMF Leading-edge manoeuvre flap.
lemon Aircraft seriously lacking in power, performance
and/or manoeuvrability (colloq.).
Lemonnier Class of resonant valveless pulsejets, named
for inventor.
LEN 1 Low-entry networking.
2 Large extension node.
len Length.
Lend Lunar-exploration neutron detector.
length Aeroplanes normally measured in flight attitude
along OX axis with perpendiculars aligned with extremities
of fixed airframe, normally including pitot or
instrument booms; helicopters, must specify whether fuselage
only or ‘rotors turning’, the latter being distance
between perpendiculars to OX axis through periphery of
rotor discs. Main cause of confusion is that measure is
frequently taken from Station Zero at a location (often an
arbitrary distance) in front of nose of aircraft. NATO
measure is always major body * ignoring nose probes or
booms, guns, FR probes, inlet centrebodies, rudder or
tailplane overhang or any other projection or rotor blade.
SI unit is metre m = 3.28084 ft = 39.37008 in.
Lens Laser-engineered net shape.
lenticular Having shape resembling side elevation of
double-convex lens, with two arcs of large curvature
meeting at pointed ends; thus * blade, a supersonic fan or
compressor profile, and * cloud, found at tops of waves in
lee of hills.
Lenz’s law Current induced in circuit moving relative to
magnetic field will generate its own field opposing motion.
LEO Low Earth orbit, parameters of which depend
upon satellite mass, density, lifetime and other variables.
Leosat Low Earth-orbiting satellite.
LEP 1 Light-emitting polymer.
2 Life-extension program[me].
L EPN Effective perceived noise level, with tone/duration
correction. See noise.
L EQ, L eq Energy-average sound pressure level.
LER 1 Leading-edge radius.
2 Long-endurance rotorcraft.
3 Laser event recorder.
LeRC Lewis Research Center (NASA).
LERX, Lerx Leading-edge root extension, pronounced
‘lurks’.
LES 1 Leading-edge slat.
2 Large-eddy simulation.
3 Land Earth station.
4 Launch escape system.
LESA Lightweight electronically scanned array.
LESM Lightweight ESM (1).
LESO, Leso LES (3) operator.
LESS Leading-edge subsystem (Space Shuttle).
LET Launch and escape time (strategic bomber, cruise
missile).
let-down Complete procedure from TOD at end of
cruise through the approach to landing; term concerned
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