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Believe me, I understand, Finn.
NO ONE wants to know the reason more than
yours truly. I mean I missed the only tail wind I ever had
to Florida. It would be easy to say "foreign object , poor Ed
should have used a filter" {:>) (and I'm going to), however, I can find
no evidence of a foreign object - no nut/bolt heads impressed into the
rotor/housing, etc. The only scrape on the rotor looks to me as if
something the size of a piece of apex seal got slid along the rotor as that area
was being compressed. It actually plowed up a small ridge of metal ahead
of it - I'm convinced that was caused by the broken seal. Now even if I'm
correct about that does not mean that the seal could not have been
originally broken by a small foreign object - long departed.
But lacking evidence of a foreign object and
finding both the apex seals and the slots worn past the specification limit - I
lean to an apex seal which broke under stress and angles of forces that it was
not designed for.
If you believe it was foreign object damage, my
suggestion is put a filter on your intake and sleep well - I certainly can't
prove it wasn't. Certainly the fact that I seem to be the first/only
flying rotary to have tried to digest an apex seal (Chuck Dunlap tried to digest
a bolt - doesn't count), then its not something that seems to be ready to happen
everywhere. Could have been just the right circumstances all occurring at
the same time that caused my failure.
Ed
----- Original Message -----
Sent: Saturday, April 23, 2005 10:13
AM
Subject: [FlyRotary] Re: All Parts have
arrived, Whew!
Thanks Ed.
Well, if it were the brittle seals breaking
then we should be safe with Bruce's & RWS's seals, even with excessive
wear.
I just hate a major failure like that without a positively
identified cause.
Finn
Ed Anderson wrote:
Well, a bit of wobble can indeed break apex
seals - that is one of the failure modes. Its just I didn't think my
seal slots were that worn - however after finding the were in some cases
past the 0.15mm limit set by Mazda, I think it possible that the stresses
from the "leaned over" profile broke the brittle seal. I had not
measured the compression since last year at the annual inspection - so don't
know what it was, but I agree it seemed good based on the rpm and
power. However, a slop apex seal slot will not necessarily show up as
low compression - it may still seal - but under more stress due to the
angle.
However, it could have been an foreign object,
don't know what it would have been at 7000 msl. Don't see where
anything could have laid around in the intake through my max power
take off and then break loose. Besides, there is nothing
missing. The things it could have been was a chunk of my plastic
manifold - no pieces missing, the epoxy shaping the secondary intake ports
in the lower manifold - inspected and all there.
I could find not scrape mark or impression on
the rotor housing with the broken seal - which surprised me. I will
inspect the rotor housings more carefully after I get the engine back
together in case I missed it.
I looked at the four spark plugs again
yesterday for missing pieces of ceramic cone, chunks of electrode,
etc. These are Racing plugs and seem fairly well constructed and
nothing was missing. I will be sticking them back in the new
engine - after I found their electrode is at least 5mm from the
combustion chamber. Just a coincident that the engine broke right
after I put the new spark plugs in - perhaps I was generating more power
with the new unshrouded plugs and broke the seals {:>).
So may never know for certain - could have been
just a combination of things adding up, weak fractured seal, sloppy apex
slot, etc. could have been the dust.
Ed
-----
Original Message -----
Sent:
Friday, April 22, 2005 11:27 PM
Subject:
[FlyRotary] Re: All Parts have arrived, Whew!
You all have to remember that Ed has a knack for finding
and exploring all possible failure modes - known, unknown, and yes,
even the impossible :)
Something that no one has memtioned is the
gears (end housings/rotors).
Also rotor bearings/e-shaft
clearance.
What's the consequences of out-of tolerances here?
I just
can't see that a bit of wobble of the apex seals in their grooves could
cause a seal to break.
Also, how could you have such excellent
compression with worn seals/grooves?
Sounds more like a fluke or
foreign object to me. Any chance that some carbon build-up near exhaust
ports could break loose and get jammed between seal and edge of exhaust
port?
Any telltale on the rotor housing as to where the seal
broke?
Did you *thoroughly* inspect the four sparkplugs? Any piece of
metal or porcelain missing at all?
Finn
Ed Anderson
wrote:
Well, George, I would not take
the conclusion that far. We have folks flying with several hundred
more hours than I have with no apex seal failures. In fact to the
best of my knowledge, I am the only one I am aware of other than Chuck
Dunlap who's rotary engine swallowed a 1/4" dia steel bolt (it was
retained - so we know) to have an apex seal failure in an
aircraft. However, I do believe that folks need to be more aware
of the true condition of their used engine components - I know all
probably did was look at it and not seeing any obviously defects or
dings said - "good to go!"
As you know, Leon is convinced my
apex seal failure was also due to foreign object ingestion - I certainly
can not prove it was something else (like the apex seal slop)
although I don't believe a foreign object to be the case -
belief is not a fact {:>).
Ed
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