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rparigor(at)SUFFOLK.LIB.N
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 Posted: Wed Aug 02, 2006 9:29 pm Post subject: Alternator failure quits engine |
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Do not arcive
Here is a story from Europa Newsgroup figured may be of interest.
Ron Parigoris
Reply-To: europa-list(at)matronics.com
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Our recently rebuilt Europa G-BWCV is again in pieces after we put only 30
more
flying hrs on this engine to add to the 50hrs it had done in the hands of
the
previous owner.
We had just received the new full permit to fly when recently, heading for
Lundy
Island just South of Bristol Docks , the cockpit filled with smoke as if a
smoke
bomb had gone off and the engine stopped! I could not discern whether the
smoke
was electrical in origin but assumed as the engine had stopped it had to
be.
The cause and subsequent sequence of events has now been established.
Alternator bearing seizure initiated dual rubber v-belt slip at the
crankshaft
pulley.
In 2-3 seconds 50 cruise hp turned both rubber belts into smoke and
vulcanised
them instead of driving the now freewheeling prop (no flywheel effect to
snap
belts).
The alternator was switched off immediately but to no benefit since its
load was
not the issue.
So instead of the crankshaft pulley driving the alternator, the alternator
now
seized was now driving the engine to a stop! A relatively minor accessory
failure
had initiated a cascade of events equivalent or even worse than a major
engine
failure.
Ofcourse this should not happen should it?
Little did I know I had become an involuntary test pilot!!!!!!!with an
observer!!!!!
The idea of a re-start attempt was not surprisingly quickly rejected.
However, as
I now know it would obviously have been a futile exercise, the engine
stopped
from 50hp running so the starter did not have a chance.
Two other aspects of this incident made for an extremely high workload.
1. I had to switch off all electrics to prevent any further risk of smoke
(if
only to be able to see out for a forced landing) or worse still fire. This
meant
I lost the electric trim.
This may appear a small thing but believe me, this meant the constant use
of one
hand flying the stick without feel and as a consequence one eye glued to
the ASI.
A workload I did not need at this time. Mechanical trim would have helped
enormously.
Try your practice forced landings in cruise trim to see what I mean. "It
could be
you."
2. The other aspect which is a little more difficult to practice was the
free
wheeling prop. All practice forced landings to date had been with the
engine at
idle as is usual. In this condition increasing speed, by diving, increases
engine
rpm so the sprag clutch is effectively connecting engine and propeller
like any
other engine.
When the engine stopped, I was quickly aware of an abnormally high rate of
descent. The prop ran away like a wind generator in hurricane, the feel of
the
stick was abnormal due to the out of trim load and I think also the
braking
effect on the airflow over the tail.of the prop now in drag parachute
mode.
The location was far from ideal for a forced landing and with the high
rate of
descent meaning short time for descent we could easily have come off far
worse
especially since the area was well populated with power lines of different
sizes
forcing a late rejection of the primary field selection.
Having taken the diagonal in anticipation of the limited field size We hit
the
far hedge in a 290 meter 30+ Celcius almost max gross with wind light and
variable as the sea breeze was backing up the Severn valley. The near
hedge
incidentally was a 6 foot steep bank from a wide drainage canal. This,
coupled
with the unusual deck angle in the glide which only got worse of course
when I
put the coupled gear and flap down on the Mono, requiring an unusually
long
duration flare as if landing up hill, put our aiming point considerably
before
the actual touch down point so we were going to hit the hedge. The last
trick I
had up my sleeve from my cross country gliding days was to drop the gear
in order
to minimise the ground roll. This in retrospect, although it did no such
thing,
probably stopped us flipping upside down. I never considered applying the
brake
but the wheel just keeps turning judging by our grass marks.Which
fortunately I
was able to pace out having vacated the aircraft.
I am giving a talk to Gloucester strut about the Europa rebuild and now
have a
new chapter.
It is in the Aeros flying club building next Tuesday at 07.30 pm and would
welcome anyone especially Subaru owners to come along.
I still like the Subaru engine and would be happy to fly it again once
this
single point failure has been addressed. If the Europa flies again it will
be
called hedgehog!
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paulm(at)olypen.com
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| Posted: Thu Aug 03, 2006 5:38 am Post subject: Alternator failure quits engine |
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Reading the fine print; this is an NSI engine.
Subaru, dual alternator belts, prop clutch, Europa, etc something unique to
the NSI EA81.
I had (last year) an identical alternator failure on my Excavator. In my
case there was only a single belt and it slipped. The diesel engine only
running at 2,000 rpm and the belt simply slipped, screamed smoked and the
engine kept running. Hard to think the small ball bearing bearing could lock
that hard but it did.
The alternator bearing opposite the pulley end had frozen solid. Really
solid! 2,200 hours since new. (PM "alternator" so no brushes)
The NSI setup with matched dual belts has a lot of drive friction and the
NSI supplied is the very common ND 55amp alternator.
Something to consider as NSI alternators were rebuilt ones. Rebuilders do
NOT always replace bearings if they pass the noise test or look ok.
Failed at 80 hours TT, not much considering.
Paul
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klehman(at)albedo.net
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| Posted: Thu Aug 03, 2006 12:39 pm Post subject: Alternator failure quits engine |
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Thank for sharing this story. Seems we were recently discussing bearing
failures.
I've never believed in dual belts for most applications unless the load
was clearly way too high for one belt. It tends to increase bearing
loads (especially if they are not well matched) and if one belt fails it
may take out the other anyway. I've never had a belt fail although I do
replace them about every 4 years or 60k miles (100k km.) on my cars and
check the tension occasionally. I did use separate belts for each of my
alternators, make sure that the pulleys were aligned, and use solid
alternator mounts, but I don't consider a single belt to be a
reliability concern. I have even accepted a very small risk that a
failed belt (for whatever reason) could foul my EJ22 camshaft belt.
Ken
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paulm(at)olypen.com
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| Posted: Thu Aug 03, 2006 1:49 pm Post subject: Alternator failure quits engine |
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The original application of the NSI dual belts was to lower the side load on
the water pump as well as belt slippage. The result was the ability to use
much lower belt tension which is a good thing. Doubles the friction and
permits lower tension with no slippage.
The NSI supplied belts are matched. Replacement belts may not be matched. I
agree mismatched belts can be a problem as well as excessive tension.
To me the issue is the widespread use of rebuilt alternators which often
have well used and or the lowest cost bearings available as rebuilders are
cost driven.
Both Vans and NSI have used rebuilt alternators. And as I have found out
rebuilt alternators is a false term in my opinion as they are only repaired
to "used auto standards" not rebuilt to "like new" standards. There is a
huge range of bearing quality for example. If the bearing is not excessively
noisy its not replaced.
The flag I see is not dual belts but the quality of rebuilt alternators
which in my opinion have no place in an aircraft.
Buy a new internal reg ND or buy a new external B and C. This incident
should be reason enough.
Paul
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