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Bill, The only time I have ever encountered "detonation" in a NA rotary engine was early on with the 86 NA engine I was flying with. I screwed up and by mistake set the ignition advance to something like 40-45 degrees BTDC. Take off and climbout were OK but when I tried to open it up and the rpm's increased I encountered a "shuddering" vibration and backed off. When I landed I took out the spark plugs and found them severely damaged. The two leading plugs had 1/2 of the ceramic center cone gone (split and broke off), the ground electrode (this was a type that had only one ground electrode) was badly eaten and gone in one case. The distance between ground and center electrode had grown to approx 1/8 -3/16". The trailing edge plugs had cracked ceramic also and the electrodes showed erosion similar to the lead plugs - just not as bad. I still have the plugs as a reminder not to over advance the ignition
However, at least on that occasion the three piece 2mm apex seals survived.
Ed
----- Original Message ----- From: "BillDube@killacycle.com" <billdube@killacycle.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, May 08, 2005 12:56 AM
Subject: [FlyRotary] Detonation? (was: Seal Hrdness)
It occurred to me after I sent the last note that perhaps detonation cased the apex seal grove to wallow out and the apex seal to fail. This is just a guess on my part.
On a piston engine, I have seen severe detonation shear the ring lands right off the pistons. This happened on a supercharged small block with stock pistons. The detonation was very severe, but brief (drag race.) The tops of the pistons did not have time to burn and melt like they would with more marginal, but long-term, detonation conditions. The force of the detonation did the damage directly rather than the high combustion temperatures.
Just a though.
Bill Dube <LED@Killacycle.com>
http://www.killacycle.com/Lights.htm
Homepage: http://www.flyrotary.com/
Archive: http://lancaironline.net/lists/flyrotary/List.html
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