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propeller width ratio
propeller width ratio Product of blade-width ratio and
number of blades; akin to solidity.
propelling nozzle That at exit from fluid jet system used
for propulsion, esp. turbojet or ramjet; for supersonic
flight variable in shape (con-di) and area.
propfan 1 Advanced propeller for use at high Mach
numbers, characterized by having six to 12 blades each
with thin, sharp-edged lenticular profile and curved scimitar
shape, overall solidity exceeding unity and loading
being high. Can be tractor or pusher, shrouded or open,
and for highest efficiency at about Mach 0.8 has two
contra-rotating units.
2 Complete engine whose thrust is generated by (1).
propjet See turboprop (colloq.).
proportional control Effect at output, eg surface movement,
is proportional to input, eg stick movement;
opposite of flicker or bang-bang.
proportional flow control A fuel control system for large
turbofans in which main flow is adjusted by precision
control of a small parallel flow [often incorporating a
pressure-drop control connected to a kinetic valve].
proportional navigation Control of trajectory in order to
home on target by changing course by several times (typically
3.5) rate of change of sightline to target; thus angular
rate of velocity vector is proportional to angular rate of
line of sight to target.
proposal Formal and comprehensive document in which
manufacturer sets out before government procurement
officials complete technical specification and performance
of proposed item, including timing and prices of
development and, possibly, production programme.
proprioceptive Pertaining to stimuli produced within
body, esp. human body, by proprioceptors.
proprioceptor Internal receptor for stimuli, such as
tendon tension, originating in somatic organ. Body
balance maintained by * plus eyes and ear laybrinths.
proprotor 1 Large propeller[s] of VTOL aircraft whose
axis can be rotated 90° to give lift.
2 Convertiplane with fixed-axis propeller[s] and lifting
rotor.
prop strike Tips of propeller[s] hitting ground, eg on
takeoff.
propulseur d’appoint Strap-on-booster (F).
propulsion efficiency Term not recommended (see
propeller efficiency, propulsive efficiency).
propulsion integration The aerodynamic integration of
the propulsion system into the air vehicle, ignoring
physical [structural] considerations.
propulsion system Sum of all components which are
required to propel vehicle, eg engine, accessories and
engine-control system, fuel system, protection devices,
inlets and cooling systems.
propulsive duct Not recommended; usually means
pulsejet or subsonic ramjet.
propulsive efficiency 1 Broadly, energy imparted to
vehicle as percentage of energy imparted to jet (from
propeller or other prime-moving device) or expended
in burning fuel. Basic equation is Froude efficiency
ηF = 1/(1 + δ V/2V) where V is velocity of vehicle and δ V
is total increase in velocity of air in jet measured as difference
between air well ahead of vehicle and that at
fastest-moving part of jet (with propeller this is well
behind plane of blades but with turbojet probably in plane
of nozzle exit). Theoretically but not practically δV could
prototype
be zero and jet would remain stationary with respect to
free-stream; ηF then is 100%. Another expression for same
relationship is ηF = 2/(R + 1) where R is ratio of jet
velocity relative to vehicle velocity, which in theoretical
perfect case becomes unity. This can also be written
–––
TV
p
, thrust times free-stream V divided by engine power.
Another treatment is * = ––––––––––––––––––––
work done on aircraft
energy imparted to jet
which reduces to –––––
2V
, where V is aircraft speed and
V+V j
V j is jet.
2 Some authorities insist definition is input energy from
burning fuel divided by energy of jet, allowing for all
engine losses, expressed as percentage.
propulsor 1 Multi-bladed fan, usually with variable
pitch or constant-speed control, used as superior alternative
to propeller; in most cases surrounded by profiled
duct.
2 Since 1980 US usage has introduced a different
meaning: the core of a turbofan engine, comprising
compressor, combustor and HP turbine.
propwash Airflow caused by propeller alone, usually
helical but velocities are measured in axial directions only.
propylene oxide Stable liquid used in rapidly dispersed
form as fuel/air explosive.
proration Actual yield of fares to carrier.
PRORO, Proro AFS code: route forecast with height
indication in pressure units.
PROSAB Parachute flare (USSR, R).
Prosat Promotional satellite.
pro-spin Tending to initiate, sustain or accelerate spin.
protected angle Selected (usually solid) angular limits of
DOA within which received signals are accepted and
amplified.
protected range Limits (eg of radius and altitude) within
which ground navaid or landing aid is protected against
interference.
protected system One incorporating maximum security
to allow electrical transmission of classified plain
language.
protection ratio Ratio of wanted to unwanted received
signal strength, eg in VOR, ADF, NDB etc.
protective breathing equipment Filtering mask donned
by airline cabin crew in event of fire in cabin.
protocol Set of rules for format and content of messages
between communicating processors or processes.
protocol control information Exchanged between peer
[open-systems] members to co-ordinate joint information.
protocol data unit The N-PDU combines the N-PCI
with the N-UD or N-SDU, the total information transferred
between peer network members.
protoflight model Qualification model of spacecraft that
is later actually flown in space.
proton Positively charged elementary particle of mass
number 1, actual mass 1.6726231 × 10 -24 g, forming part
of every complete atomic nucleus; charge magnitude
equal but opposite to that of electron e.
proton-magnetometer Family of devices usually used in
space instrumentation in which field strength is measured
by investigating effect upon atomic nuclei (eg NMR and
Larmor precession).
prototype First example(s) built of item intended for
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