Yes, MOVs can fail closed (most likely in fact) but the nice thing about
the method I am using is that if the MOV does short, the EC2 goes back to
working exactly like it does before the MOV (IF that is what I end up with) was
added. The effect of this failure in-flight would be that the mixture
would go rich but not enough to cause the engine to stop. Corrective
action would be to reach over and adjust the manual mixture control.
Today's testing was interesting in several ways. I was flight testing
the simplest possible fix (a resistive snubber) and after takeoff it seemed like
the engine was quieter. Enough so that the XM radio music in my headset
seemed louder and clearer. I know that I didn't just bump up the XM volume
accidentally because doing so requires purposefully bringing up the display and
audio menu on the Garmin in order to adjust it. The power was as
good or better than ever (~100 more rpm on climbout than usual) so a weak engine
did not explain it. I started looking at other data and
soon forgot about it and wrote it off to human perception error.
After putting the Renesis through it's paces and letting the DL1
log the engine data (what a great tool!) I landed and started my post
flight inspection routine. Then my neighbor at the south end of the
runway came over and asked me what I changed to make the engine
quieter! Hmmm...
As usual, I had made more than one change to the EC2. Besides the
snubber, I had updated the ignition advance curve in view of some recent
findings but this was a very minor change and I do not see how that could
account for a change in engine exhaust sound. I haven't looked
at the DL1 data yet so maybe there will be a clue there. Or maybe me
& the neighbor are going deaf from rotary noise.
The resistive snubber worked fine, the engine ran fine but the EM2
fuel flow sucked. With the longer injector pulses required with the
snubber installed, the EM2 did not have enough range to calibrate the fuel flow
properly. Adjusted as far as it would go, it read about 30% high at
economy cruise power setting. Simple program change to correct it but
one more 'gotcha' that I had not counted on. How come nothing is ever
simple?
Tracy
----- Original Message -----
Sent: Monday, March 12, 2007 8:31
PM
Subject: [FlyRotary] MOV fail closed? was
A solution? was : The truth??? / Injector flow rate mystery solved
Hey, Joe
Get better and worry only about getting that project
done
. You and everyone is certainly welcome
to state their viewpoint on this list - don't know of anyone banned as
yet. While all viewpoints are subject to debate and counter arguments -
that's the value of this list.
More than one viewpoint gets presented and no one
arbitrarily decides when there has been sufficient discussion - but us guys on
the list. When we get tired of it - no one is going to comment further
and you end up debating with yourself. But, that's about the extent of
anyone getting "banned".
So never hesitate to throw in your 0.02, it may be
the one that saves somebody's butt - I was not aware that a MOV could fail
closed - I thought once the magic smoke went that it did no more conducting
(or anything else) but opened up.
Ed
----- Original Message -----
Sent: Monday, March 12, 2007 5:12
PM
Subject: [FlyRotary] Re: A solution?
was : The truth??? / Injector flow rate mystery solved
My original thoughts regarding a dropping
resistor were the result of being bored while lying in bed with a 102
degree fever, otherwise I would have likely been working on my
airplane. In the end, I believe Tracy is likely the best person to
devise the ultimate solution. But in fairness to Tracy, he seems to be
a rather busy person juggling his manufacturing, airplane building,
technical support, and product development may not leave much time to work
on this particular issue. So I threw my 2 cents into the ring.
My first though was an RC circuit, but thought it may not be a reasonable
solution due to its Time/Decay rates.
Last point I would like to make is anyone
considering using a MOV "Please read the
following info:"
Like any solid state device an MOV is subject
to degradation (quickly if the power through it is greater than its heat
dissipation capacity). Further, unlike many other solid state devices
that fail in the off state when they loose their internal smoke - a
MOV can fail in the ON state.
Sincerely,
Joe (Hoping I have not offended anyone, or be
banned from FlyRotary like so many others have been from the other
list.)
----- Original Message -----
Sent: Sunday, March 11, 2007 2:30
PM
Subject: [FlyRotary] Re: A solution?
was : The truth??? / Injector flow rate mystery solved
What about MOV's?
Typical transient response time measured in
nanoseconds...
<Marv>
"Steven Boese" <
sboese@uwyo.edu> wrote:
Ed and
Joe,
The diode in the EC2 allows the current from the collapse of
the
injector magnetic field to flow to the positive supply rail (~14V);
it
doesn't oppose this. A resistor allowing this current to flow
would
also result in a close delay since the current flowing is what
maintains
the magnetic field during this delay. What is needed is a way
to
decrease the rate of voltage rise just after the EC2 pulse ends
so
arcing in the A/B selection relay is suppressed. After the
relay
contacts open enough that an arc is no longer possible (which
shouldn't
take long) an open circuit condition now would allow the
injector to
close quickly. The arcing may or may not be a problem any
given tim Ed
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