jan.mevis(at)informavia.b
Guest
|
 Posted: Tue Jun 02, 2015 9:09 pm Post subject: Engine roughness, as in stops. starts. stops. starts. |
 |
|
Hi Mark, Walt,
What I think that happens, is corona discharge in the coil.
Typically these coils start malfunctioning after 20, 30 minutes, when the
heat of the engine is well diffused into the coil.
Corona discharge is caused by imperfections in the insulation of the coil.
The original Russian (and I suppose the same for the Chinese) coils were
made manually (in labour camps !) and layer after layer of winding,
insulation resins are applied.
These resins are diluted with solvents for better applicance. And that's
where it goes wrong after some years.
The solvents evaporate and create tiny tunnels in the coil where moist air
can get trapped.
Then at higher temperature, you get discharging but not a real electrical
breakdown.
So once the coil cools down again, everything is normal again and
subsequent testing on the ground reveals no problem anymore.
The difficult issue in this theory is that we don't have an exact picture
of how it exactly happens.
I'd like to SEE it happen, but I don't have the money to investigate that.
Of course you can get other problems such as a failing capacitor.
This capacitor is only two tiny sheets of metal wrapped around with the
same insulation material applied in between.
The capacitance is rather low and if you measure it between different
coils, it varies substantially.
Modern ways of making coils first use high vacuum procedures to evacuate
all the air.
Then high-quality insulation products are applied under high pressure.
Since the wire of the secondary is so thin, it's an art to warrant the
insulation product being well applied everywhere. That's why making a new
coil is expensive.
In order to achieve a perfect insulation, you don't re-use the bakelite
flanges, but modern transformer cardboard that gets well penetrated with
insulation product.
Only my 2 cents,
Jan
On 02/06/15 22:16, "Bitterlich, Mark G CIV NAVAIR, WD"
<mark.bitterlich(at)navy.mil> wrote:
[quote]
<mark.bitterlich(at)navy.mil>
Walt > I have been trying to get my head around this theory of a "massive
discharge" etc. but have been too busy of late to sit down and think it
through. So far it just doesn't compute.
I concur. There is no failure mode that can occur that would increase
the intensity of the firing pulse above what it was designed to provide.
Walt > I have had only one coil failure in forty years of playing with
radial engines. That was in a Harvard with Bosch mags. That mag simply
quit
working, not intermittent, no bangs or whatever just simply and
permanently dead.
The interesting thing about the original Russian coil designs is that the
condenser is actually integral and internal to the coil itself. Rather
unusual. Since coils get hot, this also means the trapped heat is
applied to the condenser as well. The common discussion theme regarding
the topic under discussion (which is: Engine roughness, as in stops.
starts. stops. starts.) is that it is related to "engine heat".
Actually, I believe that is not quite accurate. I personally believe the
problem is related to HEAT IN THE COIL, which is not necessarily
synonymous with engine heat. In addition, since the coil assembly is
internal to the mag, there is no easy way to get rid of that heat and it
becomes cumulative.
If that premise is accurate, then emphasis might be placed on what
external factors increase heat in the coil since regardless of whether we
are talking coil windings, or condenser malfunction, heat is the enemy.
Kind of an "AHA" moment. Things such as spark plug gap, what spark plug
wires are used, point dwell (!!), etc., all would impact coil heat.
Best to you Walt,
Mark
-
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
