normally 12 inches from the hub. Figure 8-10
shows the blade stations of a propeller blade.
10. BLADE ANGLE (PITCH). Blade angle
is the angle formed by the chord of a section of
the blade and a plane perpendicular to the axis
of rotation. The blade angles in figure 8-11 are
representative of standard low- and high-pitch,
as well as the feather angle. These angles will vary
with different propeller installations.
11. BLADE CHORD. Blade chord is the
distance between the leading and trailing edges.
This is an imaginary line extending from the center
of the leading edge to the center of the trailing
edge. It is important for blade balancing.
12. FEATHERING. Feathering is stream-
lining the propeller blade with the relative wind.
This feature is found in most multiengined
propeller installations. Feathering serves to reduce
the drag caused by a windmilling propeller on a
dead engine and to stop rotation that could cause
Figure 8-11.-Propeller blade angles.
further damage. See figure 8-11.
13. REVERSING. A reversing propeller
allows for a negative blade angle. With a negative
blade angle, a propeller produces reverse thrust
(thrust in a direction opposite to that normally
produced by the propeller in flight). Reverse thrust
produces a braking action used during landing to
reduce the landing roll-out distance. It can also
be used to taxi an aircraft backwards.
PROPELLER MODEL DESIGNATION
The model designation for the propeller
assembly, shown by markings on the barrel,
identifies the type of propeller. The number and
letter group describes the basic model, and the
number group that follows the dash indicates the
number of minor modifications.
A breakdown of the designation of the
54H60-77 propeller is as follows:
5--Indicates the number of major changes
incorporated in the propeller.
4--Indicates the number of blades.
H--Describes the blade shank size. (The use
of a LETTER here also indicates that the
blades are made of aluminum. A NUM-
BER here would indicate the shank size,
and also that the blades were made of
steel, as in model 24260.)
60--Indicates the spline size of the propeller
77--Indicates minor modifications made to
Figure 8-10.--Blade stations.