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Al,
There's reasons for my enquiry, which involves castings for
Aviation use. My initial challenge was a multi use bellhousing to
accommodate Aussie PSRU and that of Tracy's unit.
It doubles as a engine mount and accommodates 5 ( maybe
more) starter types and has to be light and strong. This requires strong thin
wall castings.
Usually thin walled castings require pressure injection
technology. This is expensive and not cost effective because of the projected low demand, probably one to 2 hundred (at most), in an
initial 2/3 year period.
I settled on sand cast technology, but because of the
thinness of some of the pattern, the aluminium is heated beyond it's recommended
melting temps, to allow for easier running into thinner area before the temps
are reduced by the sand casting process.
The initial trial did identify obvious porosity, throughout
the pattern although later trials, being carried out in the USA have yet to
identify any significant reduction in the projected strength
requirements.
My development partner in the States, Butch as he is
affectionally know throughout the Industry - is an Aviation
Engineer.
This design has been thoroughly tested on Finite Element
Analysis, was CAD designed, with myself making the pattern to exacting
tolerances, due to design restrictions and as Butch's exacting demands - he's a
hard man to please!
Although this took some considerable time ( approx 12 months)
the pattern was completed and the prototypes done, by a very competent
foundry.
If I can quote Butch's recent remarks to me " The
Bellhousing arrived safe and sound (Excellent Packaging)..... Very Robust to say
the least, should be able to handle 800hp at least. It has been Ultrasonically
analysed for density and voids, point load tested and torque twisting along
both the horizontal and vertical axis.
Needless to say it passed with "Flying
Colours!!
Do you see a pattern developing here? Research design and
testing by competent authority!! - even the packaging!
To a unenlightened onlooker, on initially first seeing this
bellhousing, their response might be this design might not meet what we
normally accept as a bell-shaped design i.e. form not meeting design
requirements etc. etc.
This is the type of development work carried out by many
Experimental designers - but not necessarily communicated to everyone to
this degree. I won't say this is true in all Rotary installations, but I will
say there is much in the way of skilled and talented builders involved in the
process of the Rotary development.
The point I'm trying to make is, although I believe your risk
analysis is valid, I believe it is only valid when the information you base your
assessment is correct and complete. Often a valid assessment can be completely
turned on it's head when seemingly correct information is found to be
incomplete, therefore making the initial assessment completely useless. I
believe some assertions, on this discussion group, have pointed to this
possibility.
BTW I'm on the look out for any good foundries
around the East Coast Nth of Washington, who could carry out this
Bellhousing work ' Cost Effectively', for the US market, if you know
of any I would love to hear about it. One of the problems on supply to the
USA, is the 'Tyranny of Distance'.
George ( down under)
I only did hydrogen experiments with permanent mold
castings(thick wall parts), so unsure if it applies to other types. But the
experiments were conclusive. Hydrogen was absolutely trivial. It was shrinkage
porosity which dominates the mechanical properties. Hydrogen porosity develops
round voids, shrinkage voids tear.
I suspect the myth continues regarding hydrogen. I did those experiments
over 10 years ago. It gave us huge advantage over competition. We focused on
methods to reduce shrinkage defects. Ended up out performing our competition.
That was a blast. I miss those challenges.
-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
I've had a look at Al Wicks approach and for me it leaves
a lot of unanswered questions. I have the benefit of being a ( now retired)
Government Logistics manager, trained in Quality Assurance,
Occupational Health and Safety, Risk management and of course procurement. I
had a good deal of experience within the medical logistics
field.
This basic approach gives a basic guide provided you
get your facts straight and work on with the right information - I can't see
this being done with the Rotary. Perhaps he has done quite well with the
Subaru - who would know.
Al if your on here would you please elaborate on the
statement on Aluminium - the information to me is that Hydrogen is indeed
the major problem with non- injection cast aluminium. Especially if it
involves elevated thin pour castings - the elevated temperature draws
hydrogen from the air and releases it as bubbles in the aluminium, the
higher the humidity the greater the chace of Hydrogen porosity.
As we all know porosity is the primary cause of strength
reduction in a cast aluminium piece. I understand there are other causes of
porosity, but am unsure of what they all are.
George ( down under)
Ernest
Christley wrote:
Jim, Al is not
following his own process (I think I alluded to this previously). First,
you have to ask, "How many failures have accurred due to a faulty
CAS?" That's a fair question. Do you
know? Does anyone? If so, Who? Seems there was a
thread around that just a month or two ago. Intuitively, I would
say that CAS would be a single point of failure, important enough to be
remediated. The text below is copy and pasted from http://www.maddyhome.com/canardpages/pages/alwick/risk.html
The key phrase is the last sentence.
We are going to do an FMEA.
What is the goal we are trying to achieve with this process? It’s to
make sure we place our efforts on the facets which need it. Put another
way, it’s making sure we don’t waste time and effort on insignificant
items, while ignoring the truly important items.
There are only
three pieces to the puzzle. In the case
of CAS (just my guess)
1) If the component failed, how
serious would that effect the airplane? catastrophic
2) What is the probability of
the component failing? Undetermined. Start
with doing some research at NAPA et al and repair shops around how many
they sell.
3) What is the likelihood that you would notice
the problem before failure? I'd guess very
VERY remote.
You may have heard statements like “You have
to replace component x on your engine before installing into an airplane
because it represents a single point failure”. Meaning that if x fails,
there is no backup component. That statement is not meaningful until you
assess all three questions above.
Exactly.
Al's question is "... to what extent are "we" using his
methodology. My own guess would be "not much ...". Single
point(s) of failure in Tracy's ignition (and fuel control) systems - if
there are any - would be a case in point. As would redundant fuel
pumps powered by a single source, and charging systems that are not
sufficiently redundant and with appropriate indicators. If one
DOES have a single point of failure (and there are inevitably many) we
must be sure that that component is sufficiently robust to give us all
confidence that it will NOT fail.
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