|
|
You are correct, George. SAG is not really a problem with the ignition system itself.
SAG (Sparkplug Attention Getter) appears to be a result of spark plug fouling. I fly using 100LL and get 20-30 hours on a set of stock plugs before SAG starts to occur. It generally starts out infrequently and for short duration. The symptoms include:
1. First notice is a change in engine tone
2. EGT on the affected rotor will generally decrease approx 250-300F
3. RPM will drop approx 200-300
Initially it happens at high power settings (like on take off - just the place you don't want any seat cushion puckering events), but gradually as the condition gets worst (presumably more fouling of the plug) , it happens at lower power settings including cruise.
Replace the spark plugs and the conditions immediately disappear. Folks who use un-leaded/Mogas generally get considerably over 100 hours. Tracy has reported over 200 hours using the new iridium spark plugs and Mogas.
It appears to be cause by lead deposits on the ceramic center cone which cause voltage leakage leading to a weak or non-spark event at the electrodes. High power settings result in higher pressure in the combustion chamber which impedes any spark and makes it more likely to bleed off over the lead encrusted center cone.
I once had it happen right after take off with a full load of fuel and camping gear on both rotors. My heart was a pumping and the seat cushion was being punished as my rate of climb dropped to 500 fpm until I realized that in the old Cessna 150 I flew in my early days was doing good if it got 500 fpm. I circled the airport until I got high enough to feel comfortable pulling back on the power (yes, I know probably should have done it sooner - but when you don't have much altitude its sort of hard to pull the power lever) which cleared up the problem (temporarily) and continue my flight to Memphis, TN.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html
----- Original Message ----- From: "George Lendich" <lendich@optusnet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, April 28, 2008 1:51 AM
Subject: [FlyRotary] Re: three generations of ignition
Michael,
Well if it's good enough for George Graham it's good enough for me.
On the SAG issue, I was under the impression that was from fouled spark plugs. Did I get that wrong somehow?
Good to know that it uses vacuum for adjustment. The electronic points are used on the Harley and I never once had a problem with them.
That's another problem solved!
George (down under)
George:
It has a has 2 vacuum devices just like the old points system to adjust the
timing as the engine accelerates. The electronic pick-up units just replace
the points. I know George Graham ran it on his Canard and was very satisfied
with it. But he had more room to run the tall unit than I do. We exchanged a
few emails before he passed and he said it was not the best and he knew he
was leaving performance in the table but it ran so well he was reluctant to
mess with it and had the added advantage of not suffering from the dreaded
SAG issues. Sure wish he was still around so I could pick his brain a bit
more. I have read his reports in Contact Magazine as well as his posting
here many times over to learn all that I can.
Michael
----- Original Message ----- From: "George Lendich" <lendich@optusnet.com.au>
Question,
How do the electronic distributor handle advance?
George ( down under)
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
-- No virus found in this incoming message.
Checked by AVG.
Version: 7.5.524 / Virus Database: 269.23.5/1400 - Release Date: 27/04/2008 9:39 AM
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
|
|