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PEPE
PEPE Parallel-element processing ensemble (or
element).
PEPP Planetary-entry parachute program (Martin
Marietta/NASA).
PEPS, Peps 1 Positive-expulsion propellant system.
2 Pintle escape propulsion system.
PER Performance.
PERA Production Engineering Research Association
(Melton Mowbray, UK).
perceived noise level See noise.
perch position In pattern (3) with touchdown point 45°
behind.
percussion cap Detonator/igniter for ammunition activated
by sudden deformation.
percussion drilling 1 Originally, mechanical drilling hard
material by repeated physical impact, plus abrasive.
2 More recently, using a laser fired directly at the workpiece,
not [as most commonly] via a 45° mirror.
percussion gun Device for cheaply making loud bangs to
scare birds.
perfect fluid Usually implies inviscid and incompressible,
as well as homogeneous.
perfect gas One exactly obeying Joule and Boyle laws so
that PV = nRT; also obeys Charles, Gay-Lussac and
several other laws.
perforated Pierced by holes, in case of aerodynamic
surface typically removing 25–30% of projected area;
perforation of flap or airbrake can reduce actuation
power requirement and increase drag of surface, esp.
when at large angle to airflow, but destroys value of flap
as lifting surface and thus confined to divebrakes and
airbrakes.
performance 1 From operational viewpoint, ability of
system to perform, esp. expressed in numerical values.
2 From flight-safety viewpoint, ability of aircraft to
perform required functions and manoeuvres, esp. in
degraded condition and under adverse circumstances,
again expressed numerically. Subdivided into three
categories: 1, measured *, that actually recorded for
particular aircraft at particular time; 2, gross *, factored
from measured to allow for poorest aircraft in fleet,
guaranteed-minimum instead of average thrust propulsion
and possibly other degrading factors; and 3, net *,
factored from gross to allow for further possible temporary
variations (airframe damage or icing or certain
non-critical fault conditions) and minimum standard of
pilot skill and experience.
3 Narrow interpretation of numerical values of aircraft
flight limits such as speeds, altitudes and payload/ranges.
performance-command system Microprocessor-based
crew advisory system in commercial transports which
optimises performance and saves fuel.
performance factors Those deriving from aircraft
performance which affect airline traffic achieved, as
distinct from commercial and operational factors.
performance groups UK aeroplane categories: those
whose first C of A was issued before 1951 are NPG (no
performance group); those built since 1951 are Group A,
large multi-engined; B, spare; C, light multi-engined;
D, single-engined; X, foreign multi-engined imported
before particular dates.
performance index Non-dimensional comparator for
radars, derived from xmtr peak power, prf, beam width,
pulse width, antenna gain and receiver noise.
permeability
performance limiting conditions Those demanding flight
to near boundaries of flight performance or point at which
auto-ignition, stick-shaker or other subsystem is triggered.
performance management system See flight management
system.
performance number Knock rating; below 100 called
octane number.
performance reduction Historically, calculations to
reduce measured aircraft performance to standard values
at a chosen weight and in particular atmospheric pressure
and temperature.
performance-type glider Sailplane, esp. competition
sailplane.
periapsis Pericentre of orbit.
pericentre Point on orbit closest to primary.
pericynthian Point in spacecraft trajectory closest to
Moon.
perifocus See pericentre.
perigee Pericentre of Earth orbit.
perihelion Pericentre of solar orbit.
perilune Pericentre of lunar orbit.
perimeter 1 Periphery of airfield flying area.
2 Boundary of defended area.
perimeter track Taxi track linking ends of runways,
revetments or dispersals and main hangar/apron area.
period 1 Time interval between successive passages
through particular point in same direction of SHM or
1
other wave motion = ––
1
or –– . f ft
2 Time interval between successive passages through
particular bounding plane in same direction of satellite,
usually time between successive northbound transits of
Equator (orbital *); see sidereal *, synodic *.
periodic inspection Inspection, with or without teardown,
according to published schedule of time intervals
irrespective of performance (1) of device.
periodic reservation Several aircraft book slots on same
Satcom T-channel.
period of performance Timeframe in which work is done.
peripheral hem Leading edge of parachute canopy.
peripheral VLS Distributes SAM launchers along ship
to enhance survivability.
peri track Perimeter.
PERM Permanent.
Permalloy Family of American Fe/Ni alloys which are
magnetically soft, with high permeability at low magnetizing
forces.
permanent echo Terrestrial features as seen on radar at
fixed site.
permanent magnet One which retains its magnetism in
absence of strong demagnetizing field.
Permaswage Patented fluid-tight method of connecting
pipes.
permatron Gas tube similar to thyratron with magneticfield
control.
PERME, Perme Propellants, Explosives and Rocket
Motor Establishment (Westcott, Waltham Abbey, UK).
permeability 1 In magnet, ratio B/H where B is magnetic
flux induction and H is magnetizing force, symbol µ, this
is divided into absolute and relative or specific *, µ r ,
except in emu system, where * of free space is defined as
unity; measured in henry/metre.
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