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primary instruments
member through buckling (transverse movement near
centre).
primary instruments Those giving basic information on
flight trajectory and airspeed, eg traditionally horizon,
turn/slip, ASI, VSI and altimeter. Heading information
not included.
primary lighting Usually that essential for safe flight;
cockpit lighting, navigation, rotating beacon, icing,
formation.
primary member Any part of primary structure, though
not ususally applied to sheet or machined skin.
primary modulus of elasticity That for sandwich or other
multi-component material below yield point (if
applicable) of weaker component.
primary nozzle 1 That through which main flow of fuel
passes in fuel burner or injector.
2 That for primary air to combustor or airflow through
pipe of vaporizing burner.
primary radar One using plain reflection of transmitted
radiation from target, as distinct from retransmission on
same or different wavelength.
primary runway Used in preference to others whenever
conditions permit.
primary space launch One starting from Earth.
primary stress Basic applied tension or compression, as
distinct from stresses induced by deflection of structures
such as buckling.
primary structure That whose failure at any point would
imperil safety.
primary surveillance radar In ATC system, determines
aircraft range and azimuth in controlled airspace.
primary target Main target of surface-attack mission.
primary trainer That on which pupil pilot begins flight
instruction, also called ab initio, elementary (but not
basic).
primary zone See primary combustion.
PRIME, Prime 1 Precision recovery including manoeuvrable
re-entry.
2 Products comprising interdependent mechanical and
electronic parts.
prime See prime contractor or priming.
prime airlift Number of aircraft of force that can be
continuously maintained in cycle: home base, on-load
base, off-load base, recycle.
Prime Beef Worldwide Base Engineer Emergency Force
for direct combat support or to assist recovery from
natural disasters (USAF).
prime contact That for entire responsibility for design,
development and (usually) assembly and test of complete
functioning system, eg aircraft, missile etc. Manufacture,
esp. in production, may be assigned by prime contractor
to other companies or shared by consortium. An essential
is control of programme management. (Strict DoD
definition: any contract entered into directly by DoD
procuring activity).
prime contractor That awarded prime contract.
prime crew 1 Crew of strategic bomber/tanker/ICBM
flight with long experience of combat duty.
2 That assigned to fly space mission (see back-up crew)
(NASA).
prime maintenance organization A maintenance partner
to shoulder airline’s engineering responsibilities.
prime meridian Longitude 0°.
priority designated
prime mission This emerged as Pentagonese in 2004; it
varies according to class of aircraft.
prime mover 1 Source of mechanical energy, eg engine.
2 In military sense, surface vehicle designed chiefly for
towing and normally accommodating crew, ammunition
etc.
primer 1 Subsystem, usually energized by hand-pump in
cockpit, for spraying fuel into piston-engine inlet manifold
(rarely, elsewhere) to facilitate starting from cold.
2 Pressure-fed injector of atomised fuel towards igniter
in vaporising combustor to initiate combustion in starting
cycle.
priming 1 Use of primer.
2 Sensitive high explosive for detonating main charge.
priming pump Primer.
principal axes 1 Traditionally, those orthogonal axes
which eliminate product of inertia terms from equations
of motion. Modern computers make these redundant.
2 Axis of relative wind.
3 Principal inertia axis.
4 Rectilinear axes in plane of cross-section of structural
member about which moment of inertia is maximum and
minimum.
5 Loosely, any reference axes OX/OY/OZ.
principal axis of symmetry In most aircraft, the longitudinal
axis, OX or X-axis.
principal inertia axis That line passing through c.g. and
usually in place of symmetry about which long, slender
body tends to rotate when rolling; in case of aircraft actual
axis of rotation normally lies between this and wind axis.
principal parallel On oblique photograph, line through
principal point parallel to true horizon.
principal plane On oblique photograph, vertical plane
containing principal point, perspective centre of lens and
ground nadir.
principal point On oblique photograph, foot of perpendicular
to photo plane through perspective centre, usually
determined by joining opposite collimating or fiducial
marks.
principal site concept All prototypes of new combat
aircraft do entire flight-test programme at one customer
central site under close customer control (USN).
principal tensile stress For cutout in pressurized
cylinder, that along axis where stress is maximum, hence
*** factor, = maximum ***/hoop stress. For neutral hole
(ellipse in proportions 2/2) *** = hoop stress.
principal vertical On oblique photograph, line through
principal point perpendicular to true horizon.
Prind Present indication.
printed circuit Electric or electronic circuit formed by
deposition of conductive and/or semiconductive material
on insulating base; many techniques and many substrates,
eg thin/thick film, foil etc.
printed-circuit board Printed circuit on rigid substrate
provided with multiple plug-in or other contact terminals
and on which are mounted discrete devices.
printed communications Telecommunications network
providing printout at each terminal of all messages.
print reference Identifying reference of each airreconnaissance
photograph.
print-through Unwanted transfer of strong signals from
one part of magnetic tape to one pressed against it on
spool.
priority designated Two-digit number from 01 to 20
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