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streamlined
streamlined 3-D body shaped such that fluid drag is a
minimum.
streamline flow Fluid flow that is laminar and timeinvariant,
and in which each streamline is devoid of a closed
curve or sudden change in direction.
streamline position That in which a hinged or pivoted
body, eg control surface or pylon on a variable-sweep wing,
is aligned with relative wind.
streamline wire One whose section is streamlined, though
seldom optimum (usually two intersecting circular arcs).
Streams Surface-traffic enhancement and automation
support system.
stream surface 2-D sheet made up of streamlines.
stream take-off Take-off by group of aircraft in quick
succession with departure in trail formation.
stream thrust Total of pressure force and time rate of
momentum flow across any cross-section in fluid flow, F =
PA + ρAV 2 .
stream tube In a laminar fluid flow, volume of flow
enclosed by streamlines passing through upstream and
downstream closed loops (not necessarily circular) placed
normal to flow. At any point velocity is inversely proportional
to ** cross-section area.
streamwise tip Wingtip of high-subsonic or transonic
aeroplane in which leading edge is curved progressively
back parallel to local airflow to eliminate outward sweep of
isobars; one form is Küchemann tip.
street Regular procession of straightline vortices shed
alternately from above and below body, eg naturally oscillating
cylinder or wire, each vortex following same path as
next-but-one predecessor. Normally if D is body diameter,
two half-streets are separated by 1.2-D and spacing
between vortices in each half-street is 4.3 D. Also called
Kármán * or von Kármán *.
streetcar STCR (colloq.).
strength 1 Physical * is ability to withstand stress without
rupture; normally subdivided into compressive, shear and
tensile, the latter usually being stress at the yield point.
2 In radio and related fields, signal amplitude in W or dB.
3 Dielectric * is maximum potential gradient in V/mm.
strength deployment inventory Assesses individual’s
strengths/weaknesses when dealing with others (RAF).
strength test See static test.
strength/weight ratio For material, ultimate tensile
strength/density; for a structural member, breaking
stress/weight.
stress 1 Condition within elastic material caused by
applied load, temperature gradient or any other forceproducing
mechanism, measured as force divided by area.
Unit * is force per unit area normal to direction of force. It
is this force that resists externally applied loads. Common
units are MNm -2 = 0.06475 UK tons/in 2 ; kNm -2 = 0.14504
lb/in 2 ; kg mm -2 = 0.63497 UK tons/in 2 .
2 Generalized term for psychological, physiological or
mental load on organism, esp. human, which reduces proficiency.
3 Measure of resistance of viscous fluid to shear between
adjacent layers (see viscosity, Newton’s laws).
stress analysis Determination of all loads borne by all
elements of structure in all flight conditions, external
reaction points of application and direction, and allowable
and actual stresses in each member.
stress-bearing Required to resist applied load(s).
stress concentration Localized region of increased stress
stretch point
caused by sudden changes in section, poor design and
manufacturing imperfections, eg tooling marks (see stress
raiser).
stress concentration factor Peak actual local stress divided
by stress for member calculated by any standard method
without presence of stress raisers, such as sharp-corner
apertures or external surfaces. Neutral-hole * is unity.
stress corrosion 1 Metal cracking due to residual stress
from manufacturing processes or concentrated stresses
caused by flight loads and/or poor design.
2 Exfoliation corrosion.
stress cycle Complete cycle of variation of stress with
time, repeated more or less identically (very numerous for
piston-engine conrod, less for wing LCF).
stress distribution Variation of stress across cross-section
of member.
stressed skin Form of semi-monocoque construction in
which skin, nearly always metal, bears significant proportion
of flight loads, and makes principal contribution to
stiffness.
stress-free stock Selection of stock material for primary
structure in which presence of residual internal stress results
in rejection or return for further treatment; important in
heavy plate for wing skins, etc.
stressing Stress analysis of structural members, usually
while altering their design to attain optimized structure.
Stresskin Patented metal (esp. stainless) sandwich panels
requiring no supporting structure over surface.
stress raiser Local abrupt change in section resulting in
stress concentration; severity varies inversely with radius,
so that a single scratch (eg from emery particle) can over a
period initiate a fatigue crack that will eventually prove
catastrophic.
stress ratio Maximum to minimum ratio in one stress
cycle.
stress-relief annealing Heating to beyond critical temperature,
and slow cooling to relieve internal stress, eg after
cold working or welding.
stress/strain curve Plot of strain resulting from all stresses
from zero to yield point and on to rupture. Normally linear
over most of plot to yield point (limit of proportionality
where elastic deformation gives way to plastic).
stress wave Sonic pulse propagated through various
devices, eg magnetostrictive-tablet display; also called
strain wave.
stress wrinkle Visible wrinkling of skin caused by applied
load, esp. in secondary structure, eg sagging of rear fuselage
of B-52.
stretch 1 Increase in capacity of transport by adding plugs
to fuselage, normally both in front of and behind wing.
Noun and verb.
2 To apply tensile stress exceeding elastic limit.
stretchability Potential for stretch (1).
stretching 1 Process of introducing a stretch (1).
2 See stretch-wrap forming.
stretching press See stretch press.
stretch-levelling Stretching sheet or plate just beyond
elastic limit (typically 1.5% elongation) to remove all irregularities;
also called stress-levelling.
stretchout Agreement, initiated by contractor or
customer, to reduce rate of production without altering
quantity to be built.
stretch point Fuselage station at which plug is to be added
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