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Hi Jeff,
Isn't it amazing how much better you landings are - when
you are intensely focused {:>).. Seriously, glad you were where
you were when it happened and got it down safely.
While I am not a fan of any flow restriction (as you
know), I serious doubt the additional force required to pump against the
restriction would have been anywhere close to causing the problem. It
would appear - looking at the bolts - that you might have have had the
problem of loose bolts for a period of time. This can be hard to spot on
the pump pulley because as the bolts either start to elongate or back out of
their holes, the pulley would probably have moved with them - in other words,
with a causal visual inspection, you might not notice the
problem.
Most of the force on those four bolts should be in shear
as the belts force is transferred to the pulley and through the bolts to the
water pump. So it would really take a large force even to shear those
small bolts - far larger than likely could be transfer by the "V" belt system -
you belt would likely have slipped first. Just my $0.02 assessment.
This is the first I've heard of a water pump pulley coming
off - but safety wire should provide a sufficient safety measure to prevent it
from happening again.
Ed
Sent: Thursday, August 04, 2011 7:59 AM
Subject: [FlyRotary] Water pump pulley departed
in-flight
My
water pump pulley departed the flange in-flight last night … fortunately I was
right overhead on cross wind … heard a fwaap and a buzz thought something went
through the exhaust or
had lost an accessory belt;
scanned the gauges, water temp and pressure were building fast, I cut the
throttle and headed for 06 … checked
the voltmeter which showed +14V so was pretty sure at least one belt was driving
the alternator … made
my best landing in a long time then taxied back to the hangar. Probably should
have shutdown the engine right away but didn’t and it boiled over in front of
the hangar. Of course my brother was there to see this bird fly for the
first time; not exactly the demonstration I wanted. Popped the top cowling
and found the water pump pulley departed but still inside the
cowling.
The outer belt was turned completely inside-out, which is probably what made the
buzz.
There
are only four small bolts holding that thing in place … noticed in Haynes
pictures this morning that some have four studs and four bolts … guess the studs
are for adding a second pulley? –
but they would also add extra drive surface area. I
think I put those bolts on with standard loctite but am not 100% certain.
Anyway now I’m wondering if my restrictor plate, loading the pump, may have
contributed to more vibration or is this just coincidence …
Jeff
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