IVOProp

["Tim Crawford" <crawford@atdd.noaa.gov>]

Hi IVOProp People!

I have a few safety thoughts on the IVOprop to share.  

The blades are held on by friction imposed by the clamping pressure of
those 1/2" bolts torqued to 65'#.  Loose the clamp pressure & loose a
blade.  Mine IVOProp arrived with a difficult interference fit on all the
bolts.  Dry they were gallding and removing AL from the hub (i.e. Al
sticking to bolt).  Poor machine work or design!  It took 5-10 '# torque
to just turn the bolts with the gallding and lock nuts.  Further, to
remove a bolt, it had to be turned ALL the way out of the hub!  Did not
like that.  Finally, after the first 25 hr, lubricant from the prop
worm/spindle drive and engine assembly had contaminated the hub area.  Not
good if you want friction.  The key point is that this assembly should be
clean!

I removed the bolts one at a time and reamed each hole to 0.497.  Still an
interference fit but it cleaned the hole up to where bolt installation was
not a major problem and I could have confidence in bolt torque.  Then I
cleaned all the bolts, nuts and prop/flange mating surface with solvent. 
The goal to remove ALL traces of lubricant before reassembly and torque.  

Torque -- I gave up using my "snap" torque tool in favor of my old trusty
beam torque tool.  I felt it difficult to properly torque such large bolts
when I could not "feel" if the bolt was properly torqued or they were just
"hanging" on the higher static breakaway friction.  Now that I cleaned up
the holes, torquing is much less a problem.   Torque specifications for AN
hardware are dry.  Another reason to clean those bolts.  However, Duane
has told me the torque limit for 1/2" bolts is 65'#.  I looked up the
torque and 65'# is the high end of the "recommended" range.  Structurally,
the bolts will go to 90'#.  I now run up to 70'# to see if the bolts will
break free and drop to less than 65'#.  My goal is a actual torque between
65&70.

Foil tapes -- The foil tapes suggested to see if the blades are moving are
a nice thought but I believe a waist of time.  The glue is going to slip
or the tape streach before there is a indication of a problem.  I now
check the gap with a feeler gague.

Safe flying and keep the oil out of that IVOProp hub

Tim

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