My Airmaster AP308 propeller hub has served me well for about 17 years, fitted
to 3 different Rotax engines and with 4 different sets of Warp Drive blades
attached.
The latest set of replacement blades have done over 250 hours and I did
a routine servicing and inspection yesterday.
As always after removing each blade, I slide the thrust bearing assembly and
spacer
away from the blade root spigot to reveal the surface of the ferrule and
look closely for a witness line caused by the inner edge of the bearing
assembly.
On one of the ferrules there is no visible line. On the next, scratching back
and
forth with my fingernail across a faint line all the way around the ferrule
circumference doesn't result in any groove being felt. On the third, the line
is more easy to see and for about 10% of the circumference my fingernail detects
a very slight groove, maybe less than half a millimetre deep.
On previous sets of blades, I can recall deeper grooves being seen and felt
around
much of the circumference on all of the blades. Anyone I've ever asked about
this doesn't seem to have anything to offer, by way of an opinion on how much
of a groove is acceptable and whether it constitutes a significant stress riser.
So who of you has similar observations and what's your feeling about it?
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