propeller Flashcards
many types of damage cause propellers to what
fail or become not airworthy
according to FAA data, majority of propeller failures occur where
blade at the tip region, usually within several inches from the tip
what is often times the reason of failure in the tip region
crack initiator such as a pit, nick, or gouge
other possible locations of blade failure
any portion of a blade, including the mid-blade, shank, and hub, particularly when nicks, scratches, corrosion, and cracks are present
one of the principal causes of loss of airworthiness in propellers
corrosion
external corrosion where poses a serious problem
metal blades, hubs, and other components
where does internal corrosion exist
where moisture may collect in internal cavities such as hubs, blade clamps, and pitch control mechanisms
three distinct types of corrosion on metal propeller components
surface corrosion, pitting, intergranular corrosion
The loss of surface metal due to chemical or electro-chemical action with visible oxidation products usually having a contrasting color and texture to the base metal.
surface corrosion
generally results when the corrosion protection on a metal surface has been removed by erosion or by polishing.
surface corrosion
what is not recommended when dealing surface corrosion
removing paint and corrosion protection, such as when polishing blades
consists of visible corrosion cavities extending inward from the metal surface
pits
They can grow on the surface, under decals, or under improperly installed de-ice boots.
pitting
Occurs in grain boundaries
intergranular corrosion
may be the result of the continued presence of moisture such as under a decal, in a fastener hole, or where anodize and paint protective barriers have been lost
intergranular corrosion
a form of intergranular corrosion that occurs more often in forgings or rolled sheets, and less often in castings. sometimes visible as metal flaking and cracks on a blade leading edge
exfoliation
When propeller blades are bent, twisted, or cocked, they will not be properly aligned with each other in operation.
face, leading edge, or twist misalignment
vibration may cause what
loss of thrust
The level of vibration can be severe and depending on the severity of the misalignment, could lead to what
catastrophic failure
A sharp, notch-like displacement of metal usually found on leading and trailing edges. All nicks are potential crack starters
nick
The loss of material from blade surface by the action of small particles such as sand or water and is usually present on the leading edge close to the tip. This damage destroys the blades’ corrosion protection, which might lead to blade failure
erosion
These terms describing surface damage are found in Appendix 1, Glossary of Common Propeller Terms.
scratches, gouges, cuts, and scoring
When found anywhere in a propeller, cracks are cause for its immediate removal and detailed inspection. will grow over time, perhaps very rapidly, and eventually lead to failure
cracks
can be harmful, depending on their size, location, and configuration. cause local stress risers around their perimeter and at the bottom under the surface.
dents
