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Service
Bulletin #4 Jul-9-98
Purpose: To
detect blade movement inside the hub due to improper installation
and, or harmonic resonance between prop and power plant. To prevent
further flight if this situation is detected and develops in unsafe
condition (Aluminium bushings inside the blades becoming loose, breaking
bolts, blades etc..)
Introduction:
Above mentioned combinations produce high level of torsional pulses during
their firing cycle which several times exceeds their nominal torque and
also torque reversal pulses. If the prop is mounted loose and, or gets in
a harmonic resonance with the engine the blades could move inside the hub
back and forth in a plane of prop rotation.
What
to do: Prior to the next flight or airboat ride accomplish the following:
Get torque
wench and check its calibration by hanging a known weight on its arm and
multiplying the weight in pounds by arm in feet. This reading should be as
close as possible to actual recommended torque on Y2 " bolts (we
tried several torque wrenches and most of them were off by a lot).
Mark
the prop position in relation to the crankshaft. There are 2 positions to
mount 3-blade prop and 3 positions to mount the 2-blade prop. This makes a
great difference in how the prop and engine vibrate together and each
position creates totally new situation. It is impossible to determine
which position is best for your particular prop engine airframe
combination without actual testing it on it.
Recommended position on 0-360
or 10-360 engine:
3-blade -# 1 cylinder top dead center & one blade straight up.
2-blade-hand propping
position.
Torque
the 1/2" bolts to new torque value of 65 ft. X lbs.
Run
the engine momentarily on the ground through the full RPM range.
Check
the torque on 1/2" bolts and if you are not using lock nuts safety
wire the bolts.
Cut
the strips of stainless steel tape about 2 "long and 3/8 " wide
(tape supplied with this S B.
Clean
the area around gap between blades or gap between blades and blade blocks
by rubbing it with clean napkin soaked with ME. K solvent.
Apply
stainless steel tape across the gap next and parallel to mold parting
line. Use a round object to press the tape on the surface.
Follow
this inspection schedule to check if tape is broken:
After
short ground run up through full RPM range on the ground and then first
15minutes, 30minutes,
I
hour, 2hours, 4hours and then every preflight inspection. Also follow this
schedule from the beginning if the prop has been reinstalled in a
different position in relation to the crankshaft.
If
tape breaks or cracks remove the tape, clean the surface with M E. K and
apply new tape and start the inspection schedule from the beginning. ff
tape breaks again remove the prop from the service and contact IVOPROP
Corp.
Request
to dealers: please forward this S.B. and stainless steel tape to your
customers who are subject to this S. B. Keep the record of addresses of
your customers to which this service bulletin applies. Make sure that any
prop being sold to the above-mentioned combinations is accompanied with
this Service Bulletin
Compliance.-.
Mandatory
Note:
Do not use prop in 2-blade configuration without blade blocks (missing
pieces of pie, which fill out the big gaps between the blades.
POPULAR
WAYS HOW TO MOUNT PROP LOOSE
Not
torquing the bolts Do not rely on feel, Get torque wench and calibrate
it by yourself. Torque on 1/2 " bolts are 65 ft. X Lbs. (not 65 inch X
Lbs.)
Bottoming
the thread of the mounting bolts into the driving lugs or lock nuts.
Use extra washers if the bolts are too long.
Bottoming the driving lugs into the counter bored holes in our
thick aluminium plate, always make sure there is some clearance between
driving lug and bottom of the counter bored hole.
Not
having driving lugs pushed all the way into the flange.
Torquing the bolts does not generate enough force to pull the driving lung
fully in, however the vibration forces do and you loose the torque on the
bolts. Always make sure that there is not even the slightest gap between
driving lug head and the back of the flange.
Inserting
spinner composite backing plate anywhere between what bolts are
supposed to compress together, these fibreglass or composite backing
plates compress with a heat and pressure and you loose torque on the
bolts.
Using
wrong hardware
For instance if you have 1 1/4 " plate which goes on 0-320 and
you use it on 0-360 flange the milled notches will fit nicely over the
driving lugs, however their original purpose is to hold the lock nuts on
0-320 and not serve as counter bored holes for driving lugs on 0-360.
Another
example - if your 2 1/4 " diameter center boss is too long or the radius
at its base to big to accept our hardware.
If something
does not fit or it does not look right or it has more holes than you need,
do not force it together. Contact Ivoprop Corp. and get the right hardware.
Knurled
Plates Instructions Magnum Model
The
knurled plates shall be installed so that knurling finish on each plate is
in contact with the blades.
The
knurled pattern is 60 degrees symmetrical so if you reinstall the blades
between crush plates later in different position the imprint on the blades
should match the knurled pattern.
However
(because the manufacturing tolerances) to get the best match number the
blades and plates and always put the blades back in the same place.
Torque
the mounting bolts to 65ft x lb. dry (no oil or lubricant on the
thread) and run the prop momentarily through full RPM range. Re-torque the
bolts.
Repeat
the above procedure until the torque stays the same.
Install
the service bulletin stainless steel tape and follow the inspection
schedule from service bulletin. Any time you inspect the tape check the
torque on the bolts during the first four hours. After that check torque
every ten hours.
Make
sure that knurled plates supplied to you are counter bored around the bolt
holes if your blades have aluminums bushings around the bolt holes.
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