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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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