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----- Original Message -----
From: "Tommy James" <twjames@healed.org>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, September 24, 2003 6:55 PM
Subject: [FlyRotary] Coil problem or is it?
> Hi Guys,
> Today I taxied out to test the mods made to my cooling system and ran
right
> into a new and unanticipated problem.
> During the normal pre-take off engine checks, I selected "B" computer and
> then went to the coil disable switch. Pressing the switch in one
direction
> produced zero change, but the other choice produced a very noticeable
> SILENCE. Duh? Never had that one before. Taxi back. Temperatures stayed
> around 170 during this 15-20 minutes of ground running with OAT <75*
>
> It was easy to isolate the faulty Leading coil as the culprit. I talked
to
> TC who gave me the resistance values to check out 1. the resistor, 2. the
> coil, and a diagnostic procedure. Thanks, T!
> Leading coil resistor and coil tested okay.
>
> Next we checked to make sure the EC2 was functioning okay by running a
plug
> wire to an extra plug clamped to the top of the block. Fire on both A and
B
> for the leading coil. Double Duh!
> Ran the engine again and the same thing happened again. Disabling the
> Leading coil in "B" again shut the engine down.. Called TC again.
>
> Tracy suggested that it might be a plug problem. Triple Duh?! We
changed
> the leading plugs with plugs that had been cleaned with glass bead
blasting
> but were not new. The old plugs only had a couple of hours and looked
okay.
> No wear visible. A little carbon. Insulator clean.
> Cranked her up and after adjusting mixtures on both A & B for about 2600
rpm
> we test the coils.. No Problem. a little more rpm drop on B, but
> nothing major.
>
> Now, here are the pestering nagging questions: Why would relatively new
> plugs fail when given the total load? Why would both plugs fail at the
same
> time? Is there something going on that is being overlooked? Has anybody
> else ever seen this happen? (Ed/ Eddie, are you there?) Did this happen
> because I'm so close to 2R4?
>
> Be easy, guys
> Tommy James<><
>
>
Hi Tommy,
Yes, I HATE those kinds of things. If it want to fail, well OK. If it
wants to fail on the GROUND, that's Great! But, if its going to fail, it
should stay failed! I HATE intermittent and unexplained problems.
Ok, thats off my chest. Here's a possibility, Tommy. I have noticed
sometimes if I am running the mixture a tad on the lean side when I do the
RPM check with "B" controller, the engine will not just change (normal), but
falter as if going to die. I hastely reach over and crank up the mixture a
notch and I am back in business. You don't say anything about mixture, so
don't know if this could be a possible cause or not.
Now when the "SAG" occurs, it apparently does affect both plugs. The EGT
drops 300F on the effected rotor, rpm decreases around 150-200 rpm (if its
just the one rotor, if you are so lucky as to have the SAG on both rotors at
the same time (happened to me once just after take off and before I got to
pattern, the effect is more noticable like a 300-400 rpm drop. I climbed
out at 500 fpm rather than my 1100+ so was not in any danger, but the seat
cushion needed replacing. As, I say it gets your attention.
Another possibility - because I misunderstood what Tracy meant when he said
you couldn't use straight wire for the spark plug leads to mean that I had
to use resistor wires, I ended up with resistor wires and resistor plugs
(the stock plugs are resistor type). All that appeared to hasten the time
that the plugs were not apparently getting sufficient spark energy to
reliabilty jump the gap. Once I elminated the resistor sparkplug wires,
things improved considerably.
I have had SAG with as little as 20 hours of 100LL on the plugs. I have
gone as much as 50 hours, but the average is around 30 hours.
Don't know if any of these could be the cause, but if it happens again,
reach over and crank up your mixture control a notch and see if that does
anything.
Ed the EDDIE expert {:>)
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