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Hi Steve,
No problem, all appreciate the new perspective you have
brought to the topic of SAG and the hours and money you have invested. I
think this type of discussion greatly helps educate us all in whatever topic is
being discussed. Heck, sometimes we even figure out what the problem
really is which is always a plus {:>)
I got to thinking about the rise in Coolant and Oil temps
- which does support the detonation part of your theory, and I wonder whether
there is an alternate explanation since few if any seem to find evidence of
detonation - even on the plugs.
I may be one of the few flyers that have actually
experience detonation with an N/A 13B. I am 90% confident it was
detonation based on the following:
1. I inadvertently set my ignition static timing to
45 Deg BTDC (well, you don't think I would do it on purpose, do you? {:>))
and went flying
2. In those days, I couldn't get much above 5000 RPM until
after take off
3. After airborne I decided to do a WOT run - within 5 -10
seconds after opening the throttle, I noticed the exhaust note changed from its
usually roar to a clearly staccato Popping sound. I listened to it perhaps
10-20 seconds before deciding that something was decidedly different and
retarded the throttle. Landed and took the sparkplugs out.
The conditions of my plugs after experiencing detonation
were appalling.
The leading spark plugs were destroyed. The heavy
ground electrode had eroded almost back to the wall, the center electrode had
receded approx 1/8" and the ceramic cone was missing. Yes, as in GONE back down
at least 1" into the plug.
The trailing plugs were less damaged but electrode
erosion was clear and the ceramic cone on one was cracked and the second
trailing plug had a chip missing from the cone. As best I could determine
there was no damage to the engine, but that may have occurred had I not retarded
the throttle after the short duration in detonation.
Unfortunately, I was not monitoring the temps so have no
additional evidence that the engine was in detonation - but give the condition
of the spark plugs and the popping exhaust, I am convinced it was
detonation.
I know when I disable the leading plugs and just run
the engine on the trailing plugs my EGT climbs above 1700F whereas it is
normally between 1500-1600F. I suppose this is because less fuel is being
burnt in the combustion chamber and more burning in the exhaust header.
Next time I fly, I'll disable the trailing plugs and note the coolant/oil
temps and then try it with the trailing plugs disabled and see what the
temperature conditions are flying on just the leading plugs. The objective
is to see how much (if any) the running on only one set of the pair effects
coolant/oil temps under normal (non-SAG) conditions.
Ed
Sent: Thursday, September 30, 2010 10:29 PM
Subject: [FlyRotary] lead fouled plugs
The following is an exchange between Ed and me earlier today. I
hope Ed doesn't mind my forwarding it to the list.
For some reason, my replies to the list are unreasonably
large and cannot be read (at least by me) in the archives. I hope that I'm
not distributing a virus and that creating new messages instead of simply
replying works OK.
It has occurred to me that it may be possible to initiate
SAG by going to a hotter plug instead of waiting for a used one to
malfunction. If I can do this with the engine on the test stand, that
may enable studying the SAG phenomenon with less risk (to me- not necessarily
the engine). A starting point may be using stock leading plugs (BUR7EQ) in
all four locations.
Steve Boese
Ed and all,
The replacement colder plugs I thought I'd try
are:
11524-NGK Spark Plug<br>BR10EIX Racing @
9.44
as copied from the order to
Racing Beat.
As I mentioned in the talk at Paducah, I
tried all sorts of chemical cleaning methods and the lead remained on the
insulator. My thought is that the lead may
be incorporated into a glass type of phase that has
significantly less thermal conductivity than the alumina insulator. I
agree that the fact that the room temperature resistance of the material on the
insulator being over 10 raised to the 13th power ohms with the connecting points
as close as possible (about 0.030" apart) does not mean that the material
does not become conductive at higher temperatures.
The fact that the EGT drops
and the coolant and oil temperatures rise during SAG whereas
the EGT rises and the coolant and oil temperatures drop when
disabling either the leading or trailing ignition coil suggests to me
that SAG is not a result of the spark plug misfiring.
I have not seen the kind of damage to
my spark plugs that the photo of the pre-ignition shows
either.
Alternative explanations for the
observations are more than welcome and I am willing to try to test these
alternatives as much as I am able and encourage others to do the same within the
limits of acceptable risk. I have no personal investment in one theory
over another, but am just interested in understanding what is going
on.
Steve Boese
From: Ed Anderson
[eanderson@carolina.rr.com]
Sent: Thursday, September 30, 2010 11:39
AM
To: Steven W. Boese
Subject: Lead Fouled
Plugs
Hi Steve,
Was looking into colder plugs myself and came up on this
at the Champion SP site
Lead fouling can be difficult to diagnose. Although it usually
appears as yellowish brown deposits on the insulator nose, some fuel additives may also
cause similar discoloration (and are harmless). Also, a fouled plug can
typically be detected with a simple resistance tester, whereas a lead fouled plug will read within specs
(while at room temperature). Also, the ease of fouling will vary on different engines even with the same lead
exposure; this is because lead compounds combine at different temperatures.
Those formed at 370-470°C (700-790°F) having the greatest likelihood of causing
lead resistance ( fouling) on a plug.
I thought this was interesting , I know
you attempted to measure the resistance of the Lead coating. It
appears (if I read this correctly) that while normally (carbon?) fouled plugs
will give you a lower resistance reading, it appears that Lead fouled plugs will
give a normal resistance reading at room temperature. So apparently the
lead conduction (fouling) must take place at elevated (running )
temperatures. Just thought I would throw it in the hopper
{:>).
Here is a photo of what they say a pre-ignition plug looks
like - My plugs never looked like that except for the one time during first 60
hours of flight when I inadvertently set the static ignition timing to 45 Deg
BTDC. Sagged plugs never approach this condition in my
experience.
Ed
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plug damaged due to Sustained
pre-Ignition |
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