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equator
equator Primary great circle of sphere or spheroid, such
as Earth, perpendicular to polar axis.
equatorial bulge Excess of Earth’s equatorial diameter
over polar diameter.
equatorial satellite One whose orbit plane coincides, or
almost coincides, with Earth’s equatorial plane.
equi-axed Descriptive of traditional crystalline cast
metal items.
equiax blade Turbine rotor blade cast in traditional way
with random arrangement of crystal axes [often capital E].
equilibrium flow Fluid flow in which energy is constant
along streamlines, and composition at any point is not
time-dependent.
equilibrium glide Hypersonic gliding flight in which sum
of vertical components of aerodynamic lift and
centrifugal force is equal to weight at that height.
equilibrium height At which, under given conditions,
equilibrium is established between lift and weight of free
aerostat without power.
equilibrium vapour Vapour pressure of system in which
two or more phases coexist in equilibrium; in meteorology
reference is to water unless otherwise specified.
equinox 1 Instant that Sun occupies one equinoctial
point.
2 One of two points of intersection of eliptic and celestial
equator, occupied by Sun when declination is 0°; also
called equinoctial point.
equi-period transfer orbit Orbit differing from first but
having same period, eg that of lunar module following
separation from command module.
equipment Type or class of aircraft used or to be used on
particular air-transport route(s).
equipment configuration report Real-time all CMC, P/N
S/N and DB/N.
equipment interchange Agreement allowing aircraft to
fly long routes over sectors of two or more carriers, crew
being changed so that each carrier flies its own sectors.
equipment operationally ready Weapon system is
capable of safe use and all subsystems necessary for
primary mission are ready (USAF).
equipped empty weight Measured weight of individual
aircraft including removable and other equipment but less
disposable load.
equi-signal zone Zone within which aircraft receives
equal signals from left and right intersecting lobes, giving
continuous on-track signal.
equivalence ratio Ratio of stoichiometric to experimental
air-fuel ratios.
equivalent airspeed See airspeed.
equivalent brake horsepower See equivalent horsepower.
equivalent circuit Theoretical circuit diagram electrically
equivalent to practical circuit or device.
equivalent drag area See equivalent flat-plate area.
equivalent flat-plate area Area of square flat plate,
normal to free-stream relative airflow, which experiences
same drag as the body or bodies under consideration;
usually written f = D/½ρ V 2 α.
equivalent flight hours 1 The equivalent actual flight time
simulated in an accelerated fatigue test.
2 A yardstick [C-130 EFH] established by the European
Airlift Centre to enable members to trade flight time
without the need to exchange funds (Int., 2004-).
equivalent full-throttle power The theoretical brake
horsepower which a supercharged piston engine would
equivalent wing
develop at sea level if it were run at full throttle and
maximum r.p.m.
equivalent horsepower In turboprop, sum of horsepower,
usually measured as brake hp, available at
propeller shaft plus equivalent power derived from jet
thrust by applying numerical factor to measure of thrust
(abb. ehp). See equivalent power.
equivalent isotropically radiated power Product of power
to antenna multiplied by antenna gain in a particular
direction relative to that from isotropic antenna.
equivalent kilowatt[s] SI measure of power of turboprop,
abb. ekW, see equivalent power.
equivalent monoplane Monoplane wing having same lift
and drag properties as combination of two or more wings
under consideration.
equivalent monoplane aspect ratio Wings and tip vortices
of biplane mutually interfere; Prandtl showed increase in
induced drag of each wing is: ∆Di = ––––––––––
σL 1 L 2
where
½ρV 2 πb 1 b 2
σ is Prandtl interference factor, L wing lifts, b spans, and
½ρV 2 dynamic head. Total added induced drag is twice
that of single wing, so ****
b 2 L
O
1
= –––
––––––––––––
µ 2 (1 + r) 2
where
S M N µ+ 2σµr +r 2 P
Q
b 1 is longer span, S total area, μ ratio –––––––
shorter span
–––– , and
longer span
r ratio –––––––––––––––
shorter-span lift
longer-span lift
equivalent pendulum Freely gimballed platform usually
incorporating gyros and accelerometers, which has same
period of oscillation as simple pendulum of particular
length.
equivalent perceived noise level LPNeq, = L E - 10 log T/t 0
where L E is aircraft exposure level, T is total period of
noise and t 0 is (usually) 1s (see noise).
equivalent potential temperature Temperature given
sample of air would have if brought adiabatically to top
of atmosphere (ie to zero pressure) so that all water
vapour is condensed and precipitated, remaining dry air
then being compressed adiabatically to 1,000 millibars.
*** is therefore determined by absolute temperature,
pressure and humidity.
equivalent power See equivalent horsepower; in SI units
power is measured in W or multiples thereof; to a firstorder
approximation ekW = kW + 68F n where F n is
residual jet thrust in kN. In Imperial units jet thrust (lb
force) is typically multiplied by 0.3846 [reciprocal 2.6]
before being added to shaft power.
equivalent shaft horsepower See equivalent horsepower.
equivalent single-wheel load Mass which, supported by
single wheel of size just large enough not to sink significantly
into surface, causes same peak bending moment in
airfield pavement as particular truck, bogie or other
multi-wheel gear of actual aircraft.
equivalent still-air distance The distance over the ground
the aircraft would have covered in the absence of wind.
equivalent temperature Temperature particle of air
would have if brought adiabatically to top of atmosphere
(ie to zero pressure) so that all water vapour is condensed
and precipitated, remaining dry air then being compressed
adiabatically to original pressure.
equivalent wing In stress analysis, same span as actual
wing, but with chord at each section reduced in propor-
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