genaperevedent(at)yahoo.c
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 Posted: Mon Jul 31, 2006 1:53 pm Post subject: Yak-List Digest: 6 Msgs - 07/29/06 |
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Appoligies for interruption.Issue not entirely related
to magneto coil problem. During this very hot days
occasions of fuel pump cavitation might be present.
Returning to magneto coils, defects with symptoms
identical, we cured by changing HT leads in some
instances.
Gena.
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EMail Version of Today's List Digest Archive
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| Quote: | Yak-List Digest Archive
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Total Messages Posted Sat
07/29/06: 6
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Today's Message Index:
----------------------
1. 03:58 AM - M14P misfiring (Bruce Thomas)
2. 04:27 AM - Re: M14P misfiring (A. Dennis
Savarese)
3. 03:52 PM - Re: M14P misfiring (Roger Kemp)
4. 04:21 PM - Re: M14P misfiring (A. Dennis
Savarese)
5. 04:36 PM - Misfiring (Roger Kemp)
6. 07:28 PM - MiG-21 Heads Up Display (Tim
Gagnon)
________________________________ Message 1
_____________________________________
Time: 03:58:38 AM PST US
From: "Bruce Thomas" <bvthomas(at)bigpond.com>
Subject: M14P misfiring
Hi All,
I have a problem that I will tell you about in the
hope that somebody
can throw some light on it.
Last Wednesday Garry Mitchell of Australian Air
ferry and myself took
off from White Waltham Airfield In the UK in my
newly acquired Yak 18T.
We were bound for Genoa Italy as the first leg of a
long trip which was
to end in Melbourne Australia.
After 30 minutes flying we cleared English airspace
and were handed to
Paris control and were given clearance to climb to
8000 ft. from 2500ft
over the English channel, shortly after passing
through 3500ft the motor
at climb power,82%, the engine gave one cough as if
power was completely
turned off then instantly back on.
This concerned us, but it continued to run well and
smoothly, Ok as
smoothly as a M14P can , then about one minute later
all hell broke
loose; It began coughing and popping and loosing
power. The fuel and oil
pressure gauges were oscillating to zero then almost
instantly back to
full pressure again ( I don't know if this was a
cause or an effect )
however it continued to run albeit without much
power, Garry tried
various minor adjustments without being too
adventurous as we were over
water at this stage and didn't want to kill what
power we had.
.
We declared an emergency and London control vectored
us back towards
Shoreham airfield at Brighton, about 12 miles back,
luckily we made it
having lost about 2500ft.
As we dropped the gear and flap then went to full
fine pitch prior to
landing, the banging and backfiring stopped and we
were able to land
normally, the motor ran well during taxi and also
ran cleanly at 65% for
30 sec, at shut down.
We rang Russian engineering at White Waltham and ran
the symptoms past
Genna and Atur
and they thought it was magnetos, and bought two new
units to Shoreham
next morning and fitted them. Did comprehensive run
up checks and
pronounced it cured,
Alex Berry , the previous owner, then flew her back
to White Waltham,
without incident, to be dissembled and packed into a
container to be
shipped to Australia as both Garry and I at this
point decided that we
didn't have the confidence to attempt another 12000
mile trip again.
On reflection we are inclined to think that it was
fuel starvation,
rather than magneto's that caused the problem, and
will disassemble the
entire fuel supply system when it gets here.
This is where I am looking for assistance, has
anybody out there had a
similar occurrence,
or has any suggestions on what it may be and how to
cure it once and for
all.
One other point, I fitted an ignition harness from
Dennis prior to the
flight and the engine checks
at the 100 hourly indicated smoother running,
however this is not the
cause as it has done the same thing previously, but
was put down to
carby icing, a reason that I accepted at the time
but which I now do not
believe. Incidentally at the time it was CAVOC and
30o C so icing was
impossible on this day as it was on the previous
occasion. I have since
found out that the last time it was 24o C and fine.
Sorry about the long winded explanation, but it has
me stumped and I
hope some of the vast knowledge available on this
list will point me in
the right direction to avoid repitition when she
arrives home.
Kind Regards Bruce Thomas
________________________________ Message 2
_____________________________________
Time: 04:27:35 AM PST US
From: "A. Dennis Savarese" <dsavarese(at)elmore.rr.com>
Subject: Re: M14P misfiring
Bruce,
I have seen this problem several times before. When
it happens, it
typically happens somewhere between the initial 20
and 35 minutes of
flight. It has always been a bad coil breaking down
in one of the mags.
The symptom is an engine "cough" which feels like a
complete engine
shutdown for a half second or so. It DOES get your
attention. You will
have fly the airplane over your airfield for 20 - 40
minutes hoping the
engine cough will show up again. When it does,
switch to one mag then
the other. Whichever mag coil has failed will
definitely be
discernable. Remove the suspected mag and replace
the coil. Bench
=== message truncated ===
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