propeller hub and blade retention components during flight. That’s like hanging a
full dump truck off one blade. Add to that
uneven power pulses of pistons firing,
along with aerodynamic loads, and you
have components under immense strain
the entire time they’re in use. Propellers
are engineered to endure these stresses,
but improper maintenance, neglect, and
the passage of time add up and may eventually lead to failures.
The rust on this hardened-steel bearing shows that dry air
offers no assurance that rust won’t develop.
Many assume dry air helps preserve metal.
Moisture is a necessary component of rust
and corrosion processes, so the less present
the better. Russ dispelled any myths about
dry air by displaying a variety of propeller
components in different stages of decay.
Variable-pitch and constant-speed
propellers ride on hardened steel ball
bearings. These bearings allow the blade’s
pitch to change in flight. One such set
displayed by Russ had rusted so badly that
the propeller couldn’t even change pitch.
This particular airplane had lived its entire
life in the dry air of the Rocky Mountains,
and the propeller was only 6 years old.
How is that possible?
Water infiltration occurs from four
sources: pressure washers, rain, condensation, and grease. Pressure washers used
near a propeller hub exert enough force to
blast water past gaskets, seals, and grease,
damaging sensitive metal components
within the hub. Russ’ advice: Never use a
pressure washer on an airplane.
A propeller stored with its blades in a
vertical position will channel rain into the
hub. The standing water eventually makes
its way past gaskets and seals.
Condensation will occur any time the
temperature of the propeller assembly
drops below the dew point. Finally, grease
acts much like a sponge, according to
Russ. Over time, grease absorbs moisture
and breaks down, making its regular
replacement a good preventive maintenance procedure.
And what of the hub’s aluminum components? Corrosion and stress fractures are
common occurrences. One such hub had a
stress fracture that went from inside,
through the hub, and out to the mounting
flange. Had it propagated any further, it
would’ve led to a catastrophic failure of the
entire assembly, similar to the MU- 2 incident. That same hub assembly had a
blade-retaining ring with corroded
threads. Russ noted that the ring, once
mounted in the propeller assembly, has a
torque specification in the hundreds of
foot-pounds. Corrosion concentrates
stresses and may lead to a catastrophic failure of the component.
The tuning fork effect of the propeller
concentrates stress in blade anomalies.
One blade from a constant-speed propeller
was missing 4 inches of metal from the tip.
What had started out as a nick (not a
gouge) on the leading edge progressed into
a crack, ultimately leading to separation.
The leading edge of the blade had many
nicks into which a dull pencil could fit; the
paint along the edge was worn away, and
the bottom blade surface had many small
nicks from gravel strikes. What was most
interesting about the blade was that it
didn’t look much different from blades on
The gouge inside this propeller governor is advanced
corrosion; it would’ve gone undetected during even the
most thorough annual inspection. A hole in the governor
can lead to engine seizure due to oil loss.
FOR YOUR LSA or KIT PLANE
2-1/4” Panel Mount
Cat. No. A-027-100 ................ $74.50
Cat. No. A-085-100 ................ $89.95
3-1/8” Sensitive Altimeter
Cat. No. A-064-000 ............. $229.00
3-1/8” Low Range Airspeeds
Cat. No. A-066-000 ............ $119.50
Cat. No. A-065-000 ............ $119.50
3-1/8’ Rate of Climb
Cat. No. A-067-000 ............ $110.00
Cat. No. A-092-014 ................ $52.50
Cat. No. A-092-018 ................ $52.50
CHECKOUT OUR DIGITAL CATALOG
Cat. No. A-012-000 ................ $39.95
All these instruments are NON-TSO’d
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