Jim,

I think the answer may be two fold.  1.   I believe most  racing events now
prohibit the use of leaded gasoline which certainly acerbates the problem
and 2.  Racers tend not to use stock "shrouded" spark plugs which I believe
restricts the "cleaning" effect of combustion gases scouring the carbon/lead
off the center ceramic cone.

I keep intending to stick in some of the "Unshrouded" plugs that Al has
mentioned several times just to see if it makes a difference.  Perhaps I'll
purchase a set today for "next time".

Just an opinion of course.

Ed A

----- Original Message -----
From: "Jim Sower" <canarder@frontiernet.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, March 15, 2005 12:53 AM
Subject: [FlyRotary] Re: SAG Report


> I have no doubt that the SAG phenomenon is exactly as described, caused
> by as described.  I am wondering when I missed the part about it
> happening in cars or race cars or other applications.  I'm given to
> believe that there are lots of rotarys in boats and such.  I've never
> heard of it happening in anything except airplanes.  Are we running a
> little bit different ignition system?  I understand that it seems to
> have something to do with shrouded plugs, but doesn't anyone else have
> this problem with unshrouded plugs?  Would a CD ignition or something of
> the sort help?
>
> At a loss to figure out why aviators seem to be the only victims ... Jim
S.
>
> Ed Anderson wrote:
>
> > Hi Folks
> >
> > Just got back from Florida where spent weekend with Tracy and Laura.
> > Tracy and I flew to the Leeward Ranch RV Flyin on Saturday.  On the
> > way there I encountered the worst case of spark plug "SAG" ever.  We
> > were cruising at 4500 MSL when the old EGT started south dropping from
> > around 1650 to below 1400 F.  First on the rear rotor then on the
> > front rotor.  Most of the time it only happens on one rotor at a time
> > and will frequently go away after a few minutes  - not this time.
> >
> > I began getting a little concerned when both rotors were in SAG and
> > seemed content to remain there.  I tried backing off the throttle,
> > switching injector sets on and off with no avail.  This had been going
> > on for several minutes (longer than normal) when I noticed something I
> > had never noticed before - either because the SAG had never remained
> > that long on both rotors OR simply had not scan the oil and coolant
> > temps in previous sags.
> >
> > In any case, I was surprised to find the oil at 190F and the coolant a
> > 210F when with the OAT and power setting I was carrying they should
> > have both been around 165-170F.  So it clearly looked like the same
> > symptoms as overly retarded ignition timing.   This must have lasted
> > approx 15 minutes or more.  Finally on let down to the Flying location
> > the SAG went away and temps came down.
> >
> > So on the ground I took out the sparkplugs and it was clear the
> > ceramic white center was completely coated in lead/carbon - you could
> > see the lead crystal glint in the sun.  Both leading and trailing look
> > about the same - there was little to no detectable wear on the
> > electrodes just the ceramic cone black.
> >
> > Installed new spark plugs and flew it back to Tracy's and on home
> > today without further incident.
> >
> > Just wanted to pass this on because it can sure cause you to think you
> > may have fuel system problems when in reality its the spark plugs -
> > especially for any of you using Avgas as I do.
> >
> > Had a great weekend (as always) with the Crooks and was happy to join
> > them both at a birthday dinner for Laura's father on Saturday evening.
> >
> > Best Regards
> >
> > Ed
> >
> > Ed Anderson
> > Rv-6A N494BW Rotary Powered
> > Matthews, NC
> > eanderson@carolina.rr.com <mailto:eanderson@carolina.rr.com>
>
>
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