AMT_June-July_2021 - 24

SPECI AL FEATURE
" One advantage to the composite blade
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over the aluminum blade is on the composite
blades you work it down to remove
any wear, damage or delaminations and
you build it back up. So, a lot of the composite
blades have an unlimited life, " said
Marinkovich.
" You can kind of compare it to a rotor
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on your brakes. Every time you get your
brakes done they cut the rotor and it gets
a little smaller, until eventually the rotor
is below a minimum safe tolerance and
you have to throw it away and buy a new
brake rotor, " noted Marinkovich. " On the
composite blades, we sand them down to
remove any damage; we can even replace
a leading edge and then we build the layers
back up to bring it back up to the overhaul
spec. So, you grind it down and build it
back up, where the aluminum blades just
keep getting smaller until they fall below
a minimum. "
Testing and Tools
During maintenance, Hartzell may use a
variety of non-destructive testing methods
during repairs and overhauls including
fluorescent penetrant, eddy current,
magnetic particle, ultrasonic and coin
tap inspections both in the shop and in
the field to find defects in parts, explained
Frigge. " The defects can include scratches,
cracks, voids, porosity, delaminations and
debonds in steel, aluminum and composite
parts, " he continued. " Operational checks
are performed in order to confirm proper
operation of the propeller. Some of these
tests include RPM checks, feather/reverse
checks and proper operation of the de-ice/
anti-ice system. "
" There's eddy current, which is basically
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a probe-based inspection that can find discontinuities
in surface or near to surface
material, " Crowell said. " There's liquid penetrant,
which will find flaws that are open
to the surface, magnetic particle, which is
basically really similar to liquid penetrant
except that it's for ferrous steel. So, many
of the parts require those non-destructive
tests be done and they must be completely
free of any flaw. "
Of course, testing requires tooling
and Frigge stressed that it's incredibly
" We check track angle,
balance, sometimes
measure the blades at that
point, then disassemble it. "
important to use the correct tooling when
performing maintenance and tests.
" General tooling would include torque
wrenches, safety wire pliers, grease gun
and general hand tools. Specialized tooling
may also include torque wrench adapters,
shaft nut wrenches, and beta ring pullers
to facilitate propeller removal and installation.
C-clamps and spreader plates would
also be utilized when repairing composite
blades, " said Frigge.
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AMT_June-July_2021

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