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jan.mevis(at)informavia.b
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 Posted: Wed Jun 03, 2015 7:41 pm Post subject: Engine roughness, as in stops. starts. stops. starts. |
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Doc,
I thought that this list was aimed at discussing Yak / Nanchang / engine
matters, and this thread is about one of the misteries of these aircraft.
This coil behaviour is particular and has to be a consequence of the way
it is designed. Nobody really knows what happens.
So we all have to try and dig up as much information as we can and
fortunately there are some very knowledgeable people on this list who want
to share what they know.
And I am certainly not one of those very knowledgeable people.
It is near to impossible to get detailed descriptions from the
manufacturers.
Because it didn't work like that back in the USSR. Technical documentation
was State Secret, almost always.
Planes were delivered via DOSAAF to flying clubs without any real manuals.
Mechanics learned the trade from other mechanics.
If a local mechanic needed some specific information from the
manufacturer, the only way was to do a request via DOSAAF.
Last time when I was in Russia, I asked about some tech doc, and the
answer was astonishing: you have to ask DOSAAF!
Apparently that organisation still exists: a few old guys and girls in a
dusty office waiting for their pension.
Anyway, simply replacing parts without exactly knowing what's wrong, makes
me feel uneasy.
BR,
Jan
On 04/06/15 02:35, "Roger Kemp" <f16viperdoc(at)me.com> wrote:
[quote]
Okay, can the spear be removed now? In layman's terms the aged coil broke
down under chronic heat load from who knows why and puked a high voltage
discharge that resulted in a misfire somewhere in the bowels of the
engine that consumed enough fuel charge to make the engine stop for a
heartbeat puking black smoke out of somewhere under the chin of the
engine cowl resulting in sucking of the seat pack up mine and Mongooses
collective asses before the prop resumed making thrusties and we aborted
the flight landing at the nearest paved Terra firma! For those that have
never had the experience...it is fucking impressive! Not quit as
impressive as a main bearing failure in a GE 100 though. Luckily that
came on engine start. Shut that puppy down and we handed the keys back to
chief and stepped to the spare.
Anyway as I said in my one liner early in this diatribe of a
thread...change the fucking coil or both coils...it will fix the problem
and you will sleep better knowing your little magnetos are again making
voltage for your spark plugs in the normal firing order so you can break
the bonds of Terra firma and look down on all the poor schmucks stuck on
the interstates trudging along never knowing the pleasures of dancing
with the wind and cloud chasing !
Nuf said.
Doc
Sent from my iPad
> On Jun 3, 2015, at 10:16 AM, Bitterlich, Mark G CIV NAVAIR, WD
><mark.bitterlich(at)navy.mil> wrote:
>
>
><mark.bitterlich(at)navy.mil>
>
> Jan,
>
> I never considered a corona in action. Just for the sake of
>discussion, I'll mention that I measured the heat rise in a MSD Blaster
>II coil using an infra-red gun and it is significant (and it is also oil
>filled), which is kind of why I started wondering if it really is just
>engine heat that is involved. No doubt heat is contributory, but while
>it might be an insignificant point, I question whether it is all engine
>heat and not just self-induced, or maybe a combination of both.
>
> So I am trying to get my mind around this. Without creating an actual
>arc, the corona should rob energy from the coil correct? Not to
>mention if there is moist air...... there should be the formation of
>nitric acid, although since the premise is that there is such a small
>amount of air and water available, that might not be much ... but
>never-the-less there should be a chemical reaction that also would be
>contributory to insulation loss.
>
> Another thought is that the high voltage potential necessary for a
>corona to form would not be present throughout the whole coil but
>instead only near a certain percentage near the end where the voltage
>becomes "high enough" voltage to create corona loss.
>
> The problem I have with this explanation is understanding why it would
>make the engine run rough, cough, lug, etc., with the opposite mag
>operating properly? I can see where it could cause the engine to run
>rough or misfire on that one mag, but how would it do it with both
>operating?
>
> Mark
>
>
>
>
> --
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pfstelwagon(at)earthlink.
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| Posted: Wed Jun 03, 2015 7:55 pm Post subject: Engine roughness, as in stops. starts. stops. starts. |
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As an aside, in racing for years the magneto of choice was the Vertex which
had the coil internal. When Mallory came out with their magnetos they used
an external coil. Eventually Vertex went to the external coil. The MSD
magnetos used in top fuel racing use external coils and they are extremely
high output. Just for what it is worth.
Frank
---
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