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<No Sube that I know of had 2 crank sensors
All modern Subaru OEM ecu's use the method I described. They measure
integrity of sensor as described. They dump the CAS sensor if it's unstable and
use the cam sensor instead. No limping involved. I mention this because it's
such a safety advantage. It's an extremely important principal.
Obviously you can replace the cam sensor with a second CAS that's offset x
degrees. Many of the aftermarket ecu's allow such an offset. Perfect for rotary.
More important, you can do this with all sensors that can result in shut down.
For example, they'll dynamically adjust mixture unless sensor is behaving
strange. Then they use tables created when sensor was working ok. I know, you
use tables. I'm describing the concept of measuring sensor integrity, compare to
history, they go to plan B.
<Subaru also changes their crank sensing scheme more often than any
others
Yes, I've heard.
<dead in the water if the crank sensor fails.
Not true with any of the modern engines. You can prove it, just have
someone pull the plug.
-al wick
----- Original Message -----
Sent: Tuesday, September 13, 2011 1:26
PM
Subject: [FlyRotary] Re: The good news
and the bad news......
Depends on what OEM guys you are talking about.
No Sube that I know of had 2 crank sensors
except for the EG-33 six cylinder (RIP). SOME of the piston OEMs make it possible
to limp home on the Crank sensor IF it's the cam sensor that fails. In
all but one example I know of, you are still dead in the water if the crank
sensor fails. All Subarus 2005 and later are this way and most of the
ones before. Subaru also changes their crank sensing scheme more often
than any others which is a PITA for me : ).
Rotaries lack a cam sensor for obvious reasons so the partial backup
scheme is not an option.
Tracy Crook
Sent from my iPad
<An open CAS would cause instant shutdown
The Oem guys have such a brilliant solution for
this. They know from history that sensors occasionally fail. So they plan on
it. Every revolution they count the number of pulses they saw from the CAS.
So normally they see 16 pulses, with 2 breaks. The toothed wheel is missing
teeth at two different spots. One area missing 3 teeth, one missing 4 teeth.
So when they see TDC, they say "Hey, how'd the sensor do last revolution?
Did we get 16 total pulses? Did we see both a 3 tooth break and a 4
tooth break? No? Ok, then let's use the backup sensor and turn on the fault
lamp.
They also measure the integrity of the backup
sensor. Pretty simple really, it's just software calculations. Comparing to
history. The other cool thing, once you develop this logic, you have it
forever. Every future pilot has a ton of extra safety if he needs it. They
do this with all critical sensors. Oh, yeah. The other cool thing is that
the engine takes longer to start. So the user doesn't just get fault light,
they also get poor starting feedback. It's just so brilliant.
There's another important lesson here: The KISS
concept. So often true, but every once in a while it's a big mistake. Not a
good idea to blindly adopt a philosophy. Depends on the details. Two CAS
sensors are much safer if you compare readings to history, make a decision.
-al wick
----- Original Message -----
Sent: Saturday, September 10, 2011
7:09 AM
Subject: [FlyRotary] Re: The good
news and the bad news......
I agree that it sounds like electrons Bobby. An open CAS would
cause instant shutdown but I've never heard of a Mazda CAS going bad.
Have had reports of bad Subaru CAS's.
BTW, apologies for the confusion about your fuel system. I was
confusing you with Sam Hoskins who also had a recent power failure.
His sounded like fuel system problem but no further word from
him.
Tracy Crook
Sent from my iPad
What was the system voltage during run up? At what voltage does the
EC2 shutdown? Not a likely candidate.
What happens when the CAS circuit goes open? Does the EC2 stop
firing?
Will a exhaust blockage of ?% stop the engine completely? Steve's
testing showed a partial blockage has a major effect on power. Bill's
muffler had to be full of crud for that much to end up back in the
engine. If the HP2 lower cone was partly intact and came loose then a
major blockage is very possible. It would trap all the little pieces
that had been collecting in the muffler. My first HP had large chunks of
cone still intact along with all the little pieces. My second HP seemed
more intact when my incident occurred. Meaning less large chunks
appeared to be loose but plenty of the small crud. The outlet cone was
loose but more intact. I had hoped that moving the second muffler to the
belly would extend it's life but it didn't. In fact it may be more
dangerous since the small pieces can't be discharged as easily. My under
cowl muffler was mounted at a downward angle. Belly mount is almost
flat.
I agree Ed that electrons seem to be the most logical cause but may
be impossible to validate.
Bobby
Sent from my iPad
We still don't know (and may never),the causes,
but Sam's and Bills incidents based on initial information would
appear to me to be two different causes.
Sam's engine kept running - although
sputtering and producing no power - this to me sounds like a fuel
related problem (possibly vapor lock, possibly something else - could
be muffler blockage). Bill's on the other hand quit suddenly and
without any warning - that to me sounds more like an electrical
problem - either the firing pulses to the injector stopped or the
spark stopped.
If I were Bill, I would use the EC2's diagnostic
modes to check out each circuit - if one doesn't check out then that
is probably the answer. If both check OK then more head
scratching.
Ed
Sent: Saturday, September 03, 2011 9:43 AM
Subject: [FlyRotary] Re: The good news and the bad
news......
Bill,
I'm sorry to here about the damage but glad you weren't injured.
I don't know at what percentage of exhaust blockage the engine would
stop running. Also no reports on the condition of Sam's HP2 muffler.
Three aircraft experiencing very similar problems this year is too
many. If you have leading / trailing plugs and primary /
secondary injectors on separate power feeds then it should have kept
running. That leaves fuel delivery (vapor lock), CAS circuit,
Controller power, A side computer issue or muffler? I believe Sam did
switch controllers during his incident. I didn't and had plenty of
time to do so. It's now the second item in my emergency
flow.
One common item can be eliminated be removing any muffler that
has packing. Especially Hushpower 2 since they are common to all three
incidents. I'm assuming Sam's muffler also had loose
internals.
Bobby
Sent from my iPad
I
have been holding up reporting this until all the facts are in, but
that might never happen, so here we go.
Good news: No
injuries.
Bad news: I have some work to
do.
Photos at: http://www.tiny9.com/u/2101
On August 16th at 10
AM, I lined up for takeoff at my home airport (3600' paved) into a 5
knot headwind. I had just finished changing the oil and filter
and plugs. Run-up was fine, so off I went. Approximately
mid-field, and a couple of hundred feet in the air, it suddenly and
without any warning became very silent.
Hit the big switch
which puts direct battery power to everything engine, but no
noise. No more time. At this point flying the machine
becomes THE priority. Dropped the nose and was amazed to see a
little bit of runway under the nose! I had fully expected to
land in trees, houses or the river, so I dove what seemed like
straight down to capture as much runway as possible while (somehow)
holding the electric flap switch long enough to get full flaps
(noticed this later). Pulled probably my best round-out ever -
no bounce. Brakes to max and tail up for weight. I think
my sub-concious put it all the way on the nose to try to prevent
going through the fence and down the hill. Wheel skid starts
about 200 feet from the stopping point. Skid marks from the
wheel pants, cowling and prop run about the last 50 feet. It
stopped nose down just off the end. The tail was still over
pavement. Pushed the slider canopy UPHILL, stepped out and
down. Noticed that I was not even scared by the whole
event. Interesting. Never even considered trying to turn
around. Pre-thinking that non-option apparently paid
off.
More good news. No FAA or NTSB as it was a
non-reportable incident. Didn't even bend the gear legs.
Also, my neighbor crashed in a Challenger about 10 minutes earlier
at the city airport about 10 miles away. The police and rescue
types were headed that way (they had injuries) and were not
interested in my minor mishap.
As for the engine. When
we got it back to the hangar, the prop would turn only
haltingly. You could feel grinding going on inside.
First try at turning had it come up hard and stop. More
fooling with it and it gradually came looser and would turn.
Really looked like something came loose in there. Pulled a
plug from each rotor and did a compression test. Rotor 1 was
80-80-80. Rotor 2 was 2-2-2. More proof that something
had come loose. With that evidence, the insurance company
allowed me to remove the engine for inspection. What I found
was a pile of ground up ceramic junk. All the seals were still
fine. Lots of time went in to finding where that stuff came
from. Went through every inch of the induction system.
Finally Jason Hutchison (my other on-airport rotary guy) broke the
code. While the RV was standing on it's nose, this crap from
my burned-out Hushpower II ran back up the manifold and in the
exhaust port. That is what was grinding. Crap. Now
the entire thing is off the firewall including the engine
mount. All the wiring is disconnected (did not find anything
loose or missing). I spent the morning looking under the panel
for any loose or broken wiring, but found none. When I get the
EC-2 out, Jason wants to plug it into his plane and we'll do the
plugs and injectors test. If that checks out, Tracy, it is
coming to you for a good look. I don't know what else to
check. The engine quit just like somebody reached over and
turned off the ignition. No stumble, no hiccup, just instant
silence. I honestly do not know if the prop was turning or
not. I suspect not, due to the silence and the fact that one
blade is untouched.
As you can see from the photos, there was
something going on with Rotor 1. Wear is apparent down stream
from the plug holes and all 3 apex seals are starting to chip in the
center. There is quite a lot of carbon also on the rotors
after 170 hours.
Going forward, I have decided to look at
resale value for if/when my RV-12 days arrive. This means
putting a (gasp) IO-360 on it. The rotary has given me a safe
10-year run (til now, of course), so I have no regrets, but this is
an opportunity to make some changes, and parts are already on the
way. I will still be hanging out at the engine tent at S-n-F
and wherever else gatherings happen. Hope to be flying by the
first of next year....
I'm sure some of you will have
suggestions about what might have gone wrong, and I welcome any kind
of speculation, but bear in mind I am just looking at a pile of
parts and wires at this point. Both fuel pumps were on, tanks
were over half full, crank angle sensor worked fine.
Guess
it's obvious that I now have a RD-1A, EC-2, EFI Monitor
(Ed's), Felix 68/72 and Props Inc 68/72 wood props and LOTS of
engine parts (my whole 14-year stash) available! And priced to
sell!
Bill Eslick
RV-6 13B/NA EC-2
RD-1A
750
Hours
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