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Hi Al,
I certainly understand your postion. I have made all
of my (many) embarrasing moments public so indeed someone has the opportunity
not to make my mistake. Might save an engine, and aircraft and more
importantly - a life.
While I may not always agree with your viewpoint or
at least to the same degree, that does not mean I am not safey concious, nor do
I advise others to ignore safety. Every adult has to made decisions for
themselves - yes, there are plenty of people who are willing to made that
decision for you. In some cases, they are experts in the area and know
what they are taking about and in other cases ... well, they basically have an
opinion or have some experience they believe provides some insight into the
situation.
However, I still maintain that if we are going
to categorize systems as such then there are (should be) specific
perameters and specific values to be assoicated with a system that mades the
dividing line between the marginal and the "safe" system. And I
would like to be made aware of them.
My personal view is that almost any system can be operated
in some condition or set of circumstances can would cause its
effectiveness to be described as marginal.
Futhermore, I have seen examples of people fixing
"marginal" areas to the determent of other areas.
As you know, sometimes folks are inclinded to "beef" up
the area of an airframe because they believe it to be "marginal" for some
reason. Of course, what they frequently do with this "beefing" up is
simply to transfer that load (or portion of it) to some other area of the
airframe that was Not designed to carry such a load. So here a
change was made because for some reason an indivdual decided it needed beefing
up - did he do this because his structural engineering background suggested it
or because he "thought" it was marginal?
Again, without specifics, marginal is simply not a
very useful term in my book. But while I have studied and used
FMEA approaches (although not to the extent you apparently have), they are only
as good as the data and understanding that is applied in using them.
Marginal is one of those "emotional" words which
simply does not a convey very operative information - in my
opinion.
Lets take a look at my system. On my temperature
gages, I checked (on my last flight) and found that my "RED bar" for
or is 210F oil and 220F for coolant temps. Now my opinion
is that of the two that oil temperatue is the more critical - mainly because its
the internal heat removal mechanism of the rotors. I have reached
200F on the oil and 220F on coolant for those hot (90F+)
days. The vast majority of the time the oil never exceeds 195F.
The nomral coolant temps on take off on those hot days is 210F. Now
the question is what makes those "Red Bar" temperatures
magic.
If I put the "Red Bars" at 220 and 240F and only hit 200
and 210F on take off would my system now be no longer
marginal? Of course, not, we both know where the
red bar is at does not necessarily mean anything about how close or far from the
margin you may be. So what does?
There is undoubtedly some heat related conditions as
reflected in oil/coolant temperature limits which if exceeded will
unquivocably cause damage to the rotary. But, What are they? Where
can we find them? and do we understand under what conditions they occur?
For what duration must they exist for damage to occur - instanteous, 30 seconds?
five minutes?
The ONLY thing I have ever found on rotary temp limits was
that published by Racing Beat in their early 1980s technical catalog. Even
in there they describe temperature limits with cavets.
For instance they give a
coolant temp limit of 185F - then they state that if the temperature
increase rises slowly engine damage is not likely to happen even if their
stated limited was exceeded by 15 F (this brings up up to 200F) on
the other hand if the temperature rise was quick due to a broken hose, lost fan
belt, etc, then engine damage is likely. So In this case there
was a 15F difference in the point engine damage was likely to happen
- depending on the conditions.
Keep in mind that these were describing the older
13B blocks - changes have been made in the castings for the housings since then
to improve cooling (mainly due to the addition of turbochargers which
considerably increased the heat they had to get rid of). Do
they necessary change any temp limits - don't know (but I suspect
so).
Furthermore what kind of damage would exceeding the
cooling margins likely bring. Well, the first item likely to
fail experience has shown is the stock coolant "O" rings around
the combustion chambers . The orginal stock "O" rings had
the look and feel of thick rubber bands. They did not look like
they would take much heat abuse (and apparently did not) and they are
what keep the combustion gases and coolant separated - so would not be too
suprising for them to fail first.
The rotary racing crowd first took action and
started using TES "O" rings which showed much more resistance to
overheating. Now, most of us no longer use the stock coolant "O"
rings at all but instead use the Teflon Encoated Silicon TES "O" rings with
much higher temperature capability.
So does this mean we can safely exceed 200F maybe so,
maybe no. My bet is if the stock O ring was first point of failure
then switching "O" rings moved the temp limit for "O" rings beyond
240F. But, even if I were correct, we don't know for certain what
the next component to fail might be? Perhaps it fails at 210F.
In that case, the 400F coolant "O" rings don't buy us much 0r perhaps the
next failure items is at 230F. If that were the case the the change of Coolant
"O" rings buy us a nicely increased margin. I
simply do not know.
Sorry to take up so much windage, but my point is we need
to better know the failure mechanisms and their limits before we can accurately
assess a "marginal" system. If a system repeated operates and exceeds the
"marginal" limits we set and continues to operate without failure mean the
system is extrodinary, the operator is lucky?(don't you just love
that word). 0r does it means the margin assessment limits might
be too low or perhaps that we do not understand the failure
mechanism.
In any case, Al. My viewpoint is your motivation is
right on the money, couldn't agree more - if I see something I personally feel
could cause damage or particularly harm, I would speak out on it. That I
may take issue with you on some points does not in any way mean I don't
appreaciate and respect your viewpoint. I think such debate does more
to simulate thinking that any dogmatic statement. There is no doubt
in my mind that after such a debate someone, somewhere has the light bulb come
on (sometimes its even mine {:>).
By the way, did you have any luck finding
clams?
Best Regards
Ed
" In there if memory services me the limits
were
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