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critical engine
introduce changes without incurring very large costs in
item and money. Passing CDR permits the hardware
build and software coding that will result in the prototype
or other initial product.
critical engine Engine of a multi-engine aircraft, the
failure of which is most disadvantageous, due to asymmetric
effects, loss of system power or other adverse
factors; failure of ** at V 1 is basis of takeoff certification
in most multi-engine aircraft.
critical frequency 1 That corresponding to natural
resonance of blade, control surface or other structure.
2 Helicopter main-rotor blade-passing frequency at
which whole machine resonates on landing gear.
3 Frequency at which critical angle becomes zero;
highest at which vertical reflection is possible.
critical-length crack Crack of length at which application
of limit load causes failure.
critical line Locus of critical points (when track is not
known precisely).
critical Mach number 1 M crit ; Mach number at which
most-accelerated flow around a body first becomes locally
supersonic; for thin wing might be M 0.9 while thick wing
may have * below 0.75.
2 Mach number at which compressibility effects
significantly influence handling.
critical mass Mass of fissile material in which chain
reaction becomes self-sustaining.
critical part An item whose failure would imperil continuation
of safe flight.
critical path That traced through number of tasks
proceeding both consecutively and concurrently (as
during turn-round of aircraft) that determines minimum
total elapsed time.
critical-path technique Minimisation of total elapsed
time by concentrating on those elements that form critical
path.
critical point That from which two fixed bases, such as
departure airfield and destination, are equidistant in time.
critical position That over large city or mountain range
at which propulsion failure would be most serious.
critical pressure In fluid flow through nozzle, that final
pressure below which no further reduction results in
increase in flow from fixed initial pressure; usually rather
more than 50% of initial pressure (fixed ratio for any given
medium and temperature).
critical pressure coefficient C pc ; pressure coefficient at
critical Mach number, approximately given by Prandtl-
Glauert.
critical pressure ratio That at which particular axial
compressor suddenly ceases to operate efficiently due to
choking, stall or other flow breakdown.
critical speed 1 See V 1 .
2 That rotational speed at which machinery (eg, engine)
suffers dangerous resonance or whip of shafting.
critical static pressure That at critical Mach number;
symbol P c .
critical temperature That below which gas or vapour
may be liquefied by pressure alone.
critical velocity Speed at which fluid flow becomes sonic,
ie locally reaches Mach number of unity;
V cr or V crit = a (γ – 1) M
o
02 + 2
–––––––––––––
γ – 1
CRL 1 Common rail launcher.
cross-crew qualification
2 Cambridge [Massachusetts] Research Laboratory
(USAF).
CRLCN Circulation.
CRM 1 Originally cockpit resource management, now
crew resource management.
2 Collision-risk model.
3 Customer relationship, or resource, management.
CRN Common random number.
CRNA Centre Régional de la Navigation Aérienne (F).
CRO 1 Civilian Repair Organization.
2 Cathode-ray oscilloscope.
3 Community relations officer (RAF).
4 Combat recovery operation[s].
Crocco Luigi Crocco (1932) derived equation:
T = Tw (Tw Tf) ––––
u
+ –––––––––
u(Uf u)
Uf 2Cp
where T is temperature within boundary layer, Tw
temperature of adjacent solid surface, Tf free-stream
temperature, u local velocity, Uf free-stream velocity, and
Cp specific heat at constant pressure.
crocodile 1 Control surface, usually aileron, which can
split apart into upper and lower halves as airbrake; see
deceleron.
2 Covered gangway to protect passengers from slipstream,
c 1920–40.
cropped-fan engine Turbofan whose fan has been
reduced in diameter to match reduced thrust requirement
and permit LP turbine and other parts to be simplified.
cropped surface Wing, tail or other surface whose tip is
cut off diagonally at Mach angle appropriate to particular
supersonic flight condition.
cropped tip Cropped surface.
cross To pass over a fix under ATC at a specified altitude,
or a specified maximum or minimum altitude.
cross-bar System of approach lighting using straight
rows of white lights perpendicular to runway centreline.
Calvert and some other systems use several bars
decreasing in width to threshold while US practice is
single white bar followed by red undershoot zone.
cross-beam rotor Helicopter (usually tail) rotor
comprising two two-blade assemblies superimposed;
usually set at 90° but in AH-64 at 55°/125°.
cross-bleed Pneumatic pipe system connecting all
engines so that bleed from one can start, or drive accessories
on, any other.
Crossbow Code for air attacks on flying-bomb launch
sites, 1944.
cross-bracing Use of crossed diagonal wires, cables or
struts/ties to achieve a rigid structure.
cross certification To certify an item on the basis of certification
by another country.
crosscheck Brief message from one pilot to another, or
another crew member, in same aircraft giving or
confirming situation, eg “Inner marker” or “crosscheck, I
have the yoke”.
cross-cockpit collimated display Simulator display
providing large visual scene on back-projected screen
viewed in curved concave mirror, giving correct perspectives
with no discontinuities.
cross-country Flight to predetermined destination,
where landing may or may not be made, esp. one to gain
practice in map-reading and navigation.
cross-crew qualification Training course for mixed-fleet
flying.
172