|
>>So, when we talk about 'anecdotal' information,
it seems to me that the reports linking engine damage and auto spark plugs is
the true anecdotal information.<<
Except that the failures are not, at least from my
perspective, anecdotal. Good engine shops with whom I do business
every day have seen the problem engines - - and have changed their conduct
accordingly - ie, refuse to build engines for EI/automotive plug
installations. I have seen enough of the evidence to be satisfied
there is a real problem.
But leaving that aside, your comment that: "
Still, there are many auto plug installations that run just fine"
goes to the heart of the matter.
In aviation - - a lot of things
"work" or "run" just find as long as and so long as they
operate in the "center" of the operating envelope. The problems
always happen when airplanes or engines are required to operate at the edge
or boundary of the envelope. (Think of O- rings and 32d F OAT's and
the Challenger disaster).
And nobody knows where the boundary of the envelope is
with respect to automotive plugs (and even as to where it is with respect to
WHICH brand, make, or model of automotive plug).
When you say "... that still is not evidence or proof
that they should not be used." you have, in my judgment, reveresed
the question from its proper form.
The question about components in aviation should never,
in my judgment, be: "does anybody have any evidence to
show the [component] is 'bad'" .
Rather the question should be: "... does anybody
have the data to show that these spark plugs will work competently and
free of pre-ignition across the known anticipated operating envelope of
the engines into which they are to be inserted."
Regards, George
George,
I
appreciate what you are saying (and especially appreciate of the
engine-education that your company has done, particularly in the area of
LOP operations). Still, there are many auto plug installations that run
just fine. I don't find this more than a simple reliance on
hope. There is no empirical evidence that auto plugs are not up to
the task, at least for most GA applications. You advise that you
don't know what temp that auto plugs run at and whether it is within
their design range. So, when we talk about 'anecdotal' information, it
seems to me that the reports linking engine damage and auto spark plugs is the
true anecdotal information.
Engine
damage caused by pre-ignition (unrelated to the plug), mis-timing or simple
bad-luck with failure of a mechanical component at the same time that an auto
plug was near-by, is equally, or even more likely, the cause of the damage
rather than the presence of the auto plug. I'm sure you would agree that
guilt by association doesn't work for crime or mechanical
failure.
In
short, there still seems to be a lack of information, data or proof that
auto plugs, when used in similar applications to those already proven,
do not present an elevated, quantified risk, though it is your considered
opinion (not to be dismissed out of hand) that it is not a good idea. With
that said and as stated before, I fly aviation plugs and would recommend them to
anyone that asked, but that still is not evidence or proof that they should not
be used.
Chuck Jensen
Chuck,
I'm sorry if my posting was
disappointing.
But I tried to make sure it was factual and
informative. It may not be helpful - - for those that want
to go ahead and hope that the automtoive plugs will work in their
application.
I am NOT asserting that the automotive splugs are, in
fact, unsatisfactory.
What I AM asserting is that unless someone has
meaesured the actual temperature of the ceramic in the automotive plug
inserted into the aircraft air cooled cylinder then the people using the
automotive spark plug are relying on "hope as a method" to
establish safety for the configuration of their engines.
Given that there are apparently reliable reports of
pre-ignition with the use of automotive spark plugs in common aircraft engines
- - then there is hard evidence that the heat range of the plugs is marginal
at best and unsuitable in at least some portions of the normal operating
envelope.
>> What is it about auto plugs that are
inadequate? Peak temp tolerance? Temp rate of change?
Cylinder compression? 100LL gas? Where do they fall short,
...<<
I don't know where they fall short in any or all of the
areas about which you inquire. But none of those are the one about which
I am most concerned.
The operating temperature of the spark plug ceramic under
hot day high power conditions across the full range of allowable combustion
A/F ratios is the first area of concern. If it doesn't qualify there - -
then nothing else matters.
And so far as I can tell - - nobody in the experimental
aircraft world knows the answer to that question. They may be just
fine and run along at a cool 1200d F. Or not. But everybody keeps hoping
"yes" but nobody knows and nobody has the data. I assume that you agree
that hope should not be a method of assurance for safety critical items
in aircraft.
The fact that some people have run automotive plugs
successfully in some engines - - is a lot like saying that some people
have successfully used car gas in their aircraft engine.
Unless you know that they have used that gasoline under
the worst case conditions that YOU will ever encounter with your engine and
that your engine is "less critical or the same" as the engine that someone
else used - - and that when you buy your automotive gas from your local dealer
that it will be the same or equivelent gas bought from the earlier
supplier for the earlier test - - - then you really are just following
the "hope as a method" concept for assuring that your use of similar car
gasoline would work in your particular application.
I can go out and run a 350 Hp Navajo Chieftan
turbocharged engine all day at 210 Hp and do it on premium car
gas.
But if I try to run it at 230 Hp on a hot day with hot
cylinders in a single engine climb - - it is going to
detonate.
Or if I try to run it at 270 Hp on any day, it is going
to detonate.
But if I just told people that " I have run a TIO-540J2Bd
engine on car gas" - - - then it is likely that someone else will decide
to follow the "hope as a method" concept and try the same thing - - with
disasterous results.
I know what the actual heat range for the aircraft plugs
is in the high performance aircraft engine and the temperature margins that
are present.
But if I were to insert an automotive plug into a bushing
screwed into the cylinder head of my air cooled aircraft
engine I would have to merely "hope" that it was going to work
based on a mixed set of anecdotal testimonials about their successful and
unsuccessful use in aircraft engines reported by others.
That is all I am saying.
Hope is not really a method.
Regards, George
From: Lancair Mailing List
[mailto:lml@lancaironline.net] On Behalf Of Chuck
Jensen
Sent: Friday, May 30, 2008 6:06 PM
To:
lml@lancaironline.net
Subject: [LML] Re: Electronic ignition spark
plugs
George,
Your
postings are quite surprising, and a bit disappointing. You point out
that auto plugs are different that aviation plugs. You point out that
you know the temperature of the aviation plugs during operations. You
point out that auto plugs enjoys a heat sunk environment. You point out
that the aviation plug was designed for the aviation
environment.
All
of these are true, but unfortunately, you leave us to 'conclude' that that
somehow means that the auto plug are unsatisfactory in the aviation
environment. I don't like having to bridge such gaps in data.
What is it about auto plugs that are inadequate? Peak temp
tolerance? Temp rate of change? Cylinder compression? 100LL
gas? Where do they fall short, other than they are 'different' from
aviation plugs?
Personally, I run aviation plugs on both my mag and EI, but many have
run auto plugs without problems. Why, or how, were they successful when
there are so many implied deficiencies with auto plugs?
Thanks,
Chuck
Jensen
Colyn,
Other than curiosity - - it is not,
frankly, important that I know what the number is supposed to be - -
What is important is that nobody has a clue
as to what the number is for the automotive spark plug mounted in
the aircraft application.
Keep in mind that the automotive spark plug enjoyes
being "heat sunk" into a massive water cooled cylinder head that is
held at constant temperature from a thermostat.
By
contrast, the aircraft spark plug is desgined for the much more variable
environment of the air cooled cylinder head which can have temperatures more
than twice as high as the automotive cylinder head.
There is a casual acceptance of a substantial
level of "under-investigation" that is associated
with some of these often routinely accepted recommendations to use
components that have not undergone thoughtful testing at the
boundary conditions of realistic operating
environments.
Regards, George
PS> The answer to your question is in some
of the APS class materials. We made a power point slide that detailed
the aircraft spark plug ceramic temperature as a function of A/F
ratio.
George said
I can tell you the answer to that question with
respect to an aviation spark plug.
okay, what's the answer? say, 50 dF LOP 32"
TSIO-550 ....or whatever you actually
have.
|