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TERM
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DEFINITION
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Diameter
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The
diameter of the imaginary circle scribed by the blade tips as the
propeller rotates. |
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Radius
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The
distance from the axis of rotation to the blade tip. The radius multiplied
by two is equal to the diameter. |
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Blade
Face
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Pressure
Side, Pitch Side. Aft side of the blade surface facing the stern. |
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Blade
Back
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Suction
Side. Forward side of the blade surface facing the bow. |
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Leading
Edge
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The
edge of the propeller blade adjacent to the forward end of the hub.
When viewing the propeller from astern, this edge is furthest away.
The leading edge leads into the flow when providing forward thrust |
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Trailing
Edge
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The
edge of the propeller adjacent to the aft end of the hub. When viewing
the propeller from astern, this edge is closest The trailing edge
retreats from the flow when providing forward thrust. |
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Blade
Number
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Equal
to the number of blades on the propeller. |
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Blade
Tip
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Maximum
reach of the blade from the center of the hub. Separates the leading
and trailing edges. |
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Hub
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Solid
cylinder located at the center of the propeller. Bored to accommodate
the engine shaft. Hub shapes include cylindrical, conical, radius
& barreled. |
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Blade
Root
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Fillet
area. The region of transition from the blade surfaces and edges to
the hub periphery. The area where the blade attaches to the hub. |
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Rotation
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When
viewed from the stern (facing forward): Right-hand propellers rotate
clock wise to provide forward thrust. Left-hand propellers rotate
counter-clockwise to provide forward thrust. |
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Pitch
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The
linear distance that a propeller would move in one revolution with
no slippage. |
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Cylindrical
Section
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A cross
section of a blade cut by a circular cylinder whose centerline is
the propeller |
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Pitch
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Reference
line Reference line used to establish the geometric pitch ang1e for
the section. This line may pass through the leading and trailing edges
of the section and may be equivalent to the chord line. |
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Geometric Pitch Angle, a
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The
angle between the pitch reference line and a line perpendicular to
the propeller axis of rotation. |
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Controllable
Pitch Propeller
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The
propeller blades mount separately on the hub, each on an axis of rotation,
allowing a change of itch in the blades and thus the propeller. |
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Fixed
Pitch Propeller
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The
propeller blades are permanently mounted and do not allow a change
in the propeller pitch. |
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Constant
Pitch Propeller
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The
propeller blades have the same value of pitch from root to tip and
from leading edge to trailing edge. |
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Variable
Pitch Propeller
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The
propeller blades have sections designed with varying values of local
face pitch on the pitch side or blade face. |
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Rake
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The
fore or aft slant of a blade with respect to a line perpendicular
to the propeller axis of rotation. |
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Aft
Rake
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Positive
rake. Blade slant towards aft end of hub. |
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Forward
Rake
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Negative
rake. Blade slant towards forward end of hub. |
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Track
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The
absolute difference of the actual individual blade rake distributions
to the other blade rake distributions. Always a positive value and
represents the spread between individual blade rake distributions. |
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Skew
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The
transverse sweeping of a blade such that viewing the blades from fore
or aft shows an asymmetrical shape. |
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Aft
Skew
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Positive
Skew. Blade sweep in direction opposite of rotation. |
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Forward
Skew
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Negative
Skew. Blade sweep in same direction as rotation. |
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Cup
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Small
radius of curvature located on the trailing edge of blade. |
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D.A.R
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Developed
Area Ratio is blade area expressed as the percentage of a circle shaded
by the propeller. |
