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Sounds like the old Rotary SAG (Sparkplug Attention Getter), Dennis. Plug fouling caused by carbon (and lead - if using 100LL). What I first notice (in flight) is a change in engine sound. Then almost immediately the affected rotor's EGT starts to decrease by approx 200-240F from normal, rpm will then fall off a bit as well. If both rotors encounter SAG at the same time, then it WILL get your attention - although you can still produce sufficient power to maintain flight (at least in an RV). The longer this condition goes on, the worst it will become - will occur more frequently and for longer periods of time. The only fix I have found is to change the spark plugs (I have a bunch that I (one-day) will clean up and reuse. There are various things (oven cleaner,etc) that will get the carbon off the ceramic cone, but I have not found anything (yet) but blasting that will clean the lead off .
In flight, the only thing that seems to work, is to reduce power. This reduces pressures in the combustion chamber making it easier for the spark to jump the gap rather than follow a carbon/lead track on the ceramic. After a few minutes of reduced power, you can frequently run it back at higher power settings (for a while). So running at reduce power settings apparently "blows" some of the stuff off the ceramic.
The last time I encounter SAG, I decided to try disabling the Leading and Trailing coils while in flight. I found when I disabled the leading coil, the EGT would climb to almost 1700 (probably due to retarded timing), but that a few seconds of running on only the trailing coil and higher EGT seemed to clear the leading plugs and I could run for a number of minutes before the condition re-occurred.
During my early flights, For months, I though I was having a erratic injector problem - what with lower EGTs and power reduction and was pulling out my thinning hair - until Tracy mentioned that he had encounter SAG and had a fix (change spark plugs). Now, its just an aggravation but no longer a cushion cruncher when it occurs{:>)
I normally get 20-30 hours on a set of plugs using 100LL, Tracy gets over 200 hours (Mogas) in normal operation. However, when you are first tuning its normally to run with rich conditions which of course more quickly foul a plug with carbon.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html
----- Original Message ----- From: "Dennis Haverlah" <clouduster@austin.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, November 13, 2006 9:54 AM
Subject: [FlyRotary] Cleaning spark plugs
I have been running my RX -8 at low power settings while finishing up the engine install details. Recently it ran very rough and changing the plugs fixed the problem. The plugs that produced the rough running engine are the RE7A L and RE9BT iridium plugs that are standard with the Renessis car. These plugs have a thin layer of slightly moist carbon on the porcelain. Any suggestions for cleaning? Can I use a standard air operated blaster like is used on A/C plugs? I believe these plugs cost around $35! Should I be using the different plugs for the Renessis in the A/C?
Ed - Thanks for the engine data from your last flight - I plan on running some full power static tests on my A/C later this week.
Dennis H.
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