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al p wick wrote:
There are three components that define RISK. Most of your comments
address only 1 of those, the failure rate. But that's the one you use to justify dismissing the parts count in a Soob. Yes, it's a little tough to nail the fail rate on the rotary engine. I think it's a LOT tough to nail down in ANY aviation application - Lyc, Soob, V6, whatever. The other two components have equal weight. What EFFECT the failed component will have on flight. How likely to notice the defect before flight. It's not too difficult to assess those two components accurately. Those two are the no-brainers. We don't need a lot of schooling to figure out that a single CAS is a show stopper, water or oil pump is a serious but manageable situation and Oil Pressure Switch a minor annoyance. So if we have the discipline to use these methods, we've got most of the risk equation nailed. I'm getting lost here. How does mastering the no-brainers but still largely clueless on failure rate get MOST of the equation nailed? Therefore, we don't have to be precise in defining the fail rate. We just have to do our best to be moderately objective. Which brings us right back where we started. Consequence and pre-flight detection are no-brainers. We can guess at the failure rates without seriously compromising the process. Our only remaining obstacle is to become moderately objective and we now have you to impart that skill to us. Can I be forgiven if I suggest that we already have one or two moderately objective souls amoungst us, and further, that we pretty much know who they are?
But you know what this is essentially about? If we use our natural method What might this "natural method" look like? Would mine look a lot like or a lot different from yours or Cletus Johnson's? of determining risk, we make substantial judgement errors. You know
what's worse, we don't have any feedback to tell us how wrong we are. Now I'm REALLY getting lost. Up until now, I thought we were (individually and collectively) up to our ass in feedback. Folks helpless to stop telling us how wrong we are. BOY! Was I ever reading this list wrong! We tend to put more emphasis on items from recent memory, like anecdotes we heard recently. We attach significance to emotional appeals. I'm thinkin' that part will vary a lot from one individual to another. For my own part, I've been drawing lessons from the blunders (real or imagined - but often fatal) of my brethren for upwards of forty years. I like to think there are a lot of rational, level headed individuals on this list. If there is a shortage of anything, I'd say it is of hysteria. It's difficult to realize these truths. The Japanese analyzed design judgement errors, and found if they followed the FMEA approach, there were fewer failures. No doubt. But getting back to the issue at hand, what did their data look like? Were they working with two legs of the stool out of three (no data)? Or did they have ALL their shit together?
Here's an excellent example. I've seen people describe their reasoning
for going rotary. Often I would hear: "It only has three moving parts,
therefore it's safer". I suspect that 80% of you believed that. That is a gross error in perspective. No maybe, it's a huge distortion. But then again, maybe it's not. Maybe there's something important there. If it really IS a huge distortion, perhaps there's some readily available, compelling evidence to support that notion. It's a
wonderful theory, it has a component of truth in it, but totally fails
the tests for significance. This part (only my personal opinion) smells like one of those sweeping, unsupported generalities that my daddy warned me about. If a logical theory is not significant, you dump the theory. But first, you'd do well to have some really compelling evidence to support its insignificance.
When you assess risk, at some point you have to look at the whole
picture. Converting a rotary engine is extremely risky because there are
so many creative activities you are doing. As opposed to converting to a ??? (Soob? V6? Inline-4? - you pick one) engine that is devoid of/has dramatically fewer creative activities? Each has many potential
oversights, so the oversights occur. You have lot's of evidence that
describes this. The ratio of dead sticks, the number of alarm conditions, whatever you choose. But you need the courage to face the truth. It's not easy. Now I won't argue that perhaps Soob or V6 has fewer dead-sticks per installation than rotarys (largely because I don't have the data to support such a position). Can we entertain the notion that some of this might involve: a) we (the rotary community) are operating much closer to the rated peak performance of our engines than, say, your Soob; b) we are eschewing critical factory components for what we feel are [potentially - key word here] superior, more robust custom components? I can understand that such activity would increase risk initially. The (widely held, I think) hope is that these efforts will produce a more robust, reliable fuel control (for example) that will advance the state of the art down the road. The goodness or folly of that notion rests with the individual IMO. Stipulating the added risk, I must point out that the significance of such risk (not by any means quattified at this stage) must be determined by the risk taker - not by som
e umpire with a clip board.
Now if we can take VERY effective action on those risk items, the ones we have all the failure data on? Or the ones we can inutit are obviously risky? then we have a power plant that has some real potential. Many of it's failure modes are gradual, thus reducing the EFFECT of the failure. Basically giving us more time to land safely. In theory, the rotary is less prone to torsional risks...although there are indications can you share some of those? that too fails the significance test. Unless we were to include Lycs with all their crankshaft ADs, or Ivo props, or gawd knows what we'd find if the Soobs and V6s were run at or above rated rpm. We get the satisfaction of being different and thumbing our noses at nay sayers. Any auto conversion qualifies here. We contribute to what can very likely be a viable alternative that exceeds Lycoming performance on all levels. And here too.
So this guy that spent all those years looking into the root causes of
failures, hopes he'll eventually be able to explain these things well
enough, provide enough facts, that a life or two will be saved. I suppose that sounds corny, but that's my view. My view is that the pivotal aspect of his investigation was reliable failure data. Seems to me we can all pretty much agree that the rest is pretty intuitive and not at all difficult to master (even without taking night courses).
-al wick
On Mon, 06 Jun 2005 17:27:06 -0500 Jim Sower <canarder@frontiernet.net>
writes:
<... in my book, redundancy is job one ...>
The engine has demonstrated its ability to get you to the next
airport
without coolant or oil. Ignition and fuel are another matter. Dual
EWPs might be necessary for TO and climb and redundant in cruise.
Redundant oil pumps seem to me a whole lot more trouble than they're
worth.
As for CAS and the like, NAPA, dealerships etc. could provide the
least
UNreliable available as to what needs to be backed up and what
doesn't. Might even discover that you need to back up the MAP
sensor or
something of the like before the CAS on account of they fail all the
time. My point is: *who knows??*
In my view, Al's discipline and methodology work beautifully in a
factory where the same machines are doing the same thing hundreds of
thousands of times a day. It works less well for say, cars because
it's
so much more difficult to gather accurate data. How you gonna
determine
how many of some component failed after how much use? Dealerships
are a
help - they track what failed and when - but the independent shops
do
not and I'm pretty sure they do the great bulk of the repair
business.
On top of not knowing with any degree of reliability what failed and
when, we are totally clueless as to fleet mileage. Therefore MTBF
is
impossible to track unless you assume (remember that acronym) that
the
fraction of data gleaned from dealerships reflects the entire fleet
accurately. Bit of a stretch IMO.
So here we are examining airplanes. Homebuilts no less. How in
hell on
earth are you gonna' get data around failures? Al got his little
slice
off the Canard or Cozy list(s), but it was a *tiny* slice of reality
submitted by volunteers. Just for openers, I'd have to question the
*motives* of the guys who participated in his little study - and the
guys who *didn't* as well. Beyond participants' agenda, the small
size
of the sample is troubling. If one could identify all of the
suppliers
of parts and components, one might estimate MTBF of this component
relative to that component, but life expectancy in actual hours is
still
an impossible dream. Add to that the fact that Lycs on planes that
fly
all the time (like instruction, air freight, air taxi and the like)
almost always make it to TBO while the same engines on privately
owned,
rarely flown planes almost never do. Quantify *that* Tarzan! Does
that
phenomenon apply to auto conversions too? Does it matter? Damned
if I
know.
I may be mistaken here, but it seems to me that the very soul of
Al's
methodology is accurate data around the incidence of failures. He
can
speak to that better than I can, and I sure hope he does.
Additionally,
only he can speak to the degree to which data that is dirty and/or
unreliable skews the results. Basically, it seems to me that Al is
trying to quantify something that's qualitatively intuitive to
everyone
on the list. We can guess which components need attention and set
rough
priorities as to which ones to address first. The main issue is
quantifying these occurrences failure. At this juncture Al simply
does
not have the data to do this with a lot better reliability than we
could
do with educated guesses. He needs a *lot* of *good* data IMO.
I'm wondering if it's possible that he will ever get it ... Jim S.
-------------------------------------------------
Was said ...
I see guys doubling up on water pumps (2 EWP in some cases) yet
because
there hasn't been a CAS failure (that we know of) they are not
worried .
If you want true redundancy, you must double up on the systems that
have
a possibility of killing you engine (and you,no matter how remote)
The
CAS failure could be between the ECU & the CAS due to our
application.
Not to be too critical, but I've seen some pretty scary (sloppy)
installations. If you follow the certificated aircraft procedures as
far
as securing, protecting & routing wires, hoses, pipes & components
you
can be on your way to a safe installation.
Georges B. (in my book, redundancy is job one)
and ...
I fail to see how installing another CAS will 'dramatically' reduce
risk of all ECM causes.
We have already said we have no history of failure of the CAS, how
can
installing another CAS (with no history of failure), 'dramatically'
reduce the risk of failure?
And how can installing another CAS have any influence on "the risk
of
all ECM causes" ?
I also have great respect for redundant systems, but I cannot see
your
logic in this one. It is the 'dramatic reduction' that troubles me.
Homepage: http://www.flyrotary.com/
Archive: http://lancaironline.net/lists/flyrotary/List.html
-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
Homepage: http://www.flyrotary.com/
Archive: http://lancaironline.net/lists/flyrotary/List.html
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