TM 1-1500-204-23-5
b. Tip Damage. When the removal or treatment of
defects on the tip necessitates shortening a blade, shorten
each blade used with it and keep such sets of blades
together (see figure 2-4 and 2-5.). In making the repair, it
is not permissible to reduce the propeller diameter below
the minimum diameter limit shown on the airplane
specification.
c. Bends and Twists. Repair methods for bends
and twists are explained in the following paragraphs.
(1) Cold straightening. Repair bent blades in
accordance with the instructions of the manufacturer.
Carefully check the extent of a bend in face alignment by
means of a protractor similar to the one shown in figure 2-
6. Only bends not exceeding 20 degrees at 0.15-inch
blade thickness to O degrees at 1.1-inch blade thickness
may be cold straightened. Straighten blades with bends
exceeding these values only based upon recommendation
of the manufacturer, and only at the facilities having
proper heat-treatment equipment. In all cases, inspect
the blades for cracks and other injuries both before and
after straightening.
(2) Annealing method. Repair by annealing
consists of heating the alloys to an elevated temperature,
holding or soaking them at this temperature for a length of
time depending upon the mass of the metal, and the
cooling in still air. This method leaves the metal in the
best condition for cold-working.
(3) Hub damage. Repairs to steel hubs and
parts shall be accomplished only in accordance with the
recommendations of the manufacturer. Welding and
remachining is permissible only when covered by
manufacturers service bulletins.
(4) Spinner damage. Check for evidence of
dents, cracks or other visible damage. Replace if
damaged. Dents are permissible, provided they do not
affect propeller appearance while it is turning.
(5) Marking repaired blades. Mark the blades
to correspond with the manufacturer's system of model
designation to indicate propeller diameter.
(6) Painting. Paint in accordance with
instructions contained in TM 55-1500-345-23.
2-11. Propeller Balancing. Propellers must be balanced
statically, dynamically, and aerodynamically.
a. Static Balancing. Propeller static unbalance
occurs when the center of gravity of the propeller does not
coincide with the axis of rotation. Two methods of static
balancing are described in the following paragraphs.
NOTE
During a propeller static balance check,
all blades must be at the same blade
angle. Before conducting the balance
check, inspect to see that each blade has
been set at the same blade angle.
·
Unless
otherwise
specified
by
the
manufacturer,
an
acceptable
balance
check
requires
that
the
propeller
assembly have no tendency to rotate in
any of the positions previously described.
If the propeller balances perfectly in all
positions, it should also balance perfectly
in all intermediate positions. When
necessary,
check
for
balance
in
intermediate positions to verify the check
in the originally describe positions.
(1) Knife-edge method. The knife-edge test stand,
as shown in figure 2-7, has two hardened steel edges
mounted to allow the free rotation of an assembled
propeller between them. The knife-edge test stand shall
be located in a room or area that is free from any air
motion, and preferably removed from any source of
heavy vibration. The standard method of checking
propeller
assembly
balance
involves
the
following
procedures:
(a) Insert a bushing in the engine shaft hole of
the propeller.
(b) Insert a mandrel or arbor through the
bushing.
(c) Place a propeller assembly so that the
ends of the arbor are supported upon the balance stand
knife-edges. The propeller must be free to rotate.
(d) Check two-bladed propeller assemblies for
balance, first with the blades in a vertical position and
then with the blades in a horizontal position, as shown in
figure 2-7. Repeat the vertical position check with the
blade positions reversed; that is, with the blade which was
checked in the downward position placed in the upward
position.
2-10
