---------------------------------------------------------- Engines-List Digest Archive --- Total Messages Posted Thu 10/11/07: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:05 AM - Re: Engines-List Digest: 5 Msgs - 10/10/07 (Gary Casey) 2. 11:57 AM - Re: Ring Flutter? (teamgrumman@aol.com) 3. 08:11 PM - Knock sensors? (Fiveonepw@aol.com) ________________________________ Message 1 _____________________________________ Time: 06:05:29 AM PST US From: Gary Casey Subject: Engines-List: Re: Engines-List Digest: 5 Msgs - 10/10/07 I'm not a certified engine expert (although I am probably certifiable in other catagories...:-), but in my experience "ring flutter" is something the engine builder will use to explain broken rings found after a teardown. The owner will then nod and pay the bill. Presumably the the ring starts to vibrate away from the cylinder wall in waves. Some will say it can happen at very high piston speeds or with a cylinder that is badly worn - or if the cylinder pressure is rapidly changing as in a detonation event. Regardless, it is the result of something bad, not the cause of it. How someone can diagnose "ring flutter" without having torn down the engine I don't know. I certainly wouldn't lose any sleep over it, but at the same time keeping the timing correct will maintain a margin against detonation. Most naturally-aspirated aircraft engines have a robust margin anyway, except when overheating while running on one mag. Gary Casey > > Time: 04:38:19 AM PST US > From: Fredrick Kerfoot > Subject: Engines-List: Ring Flutter? > > > What is piston "Ring Flutter"?? I have an IO360. Just how > concerned shoul > d I be? > > Fred K ________________________________ Message 2 _____________________________________ Time: 11:57:33 AM PST US Subject: Re: Engines-List: Ring Flutter? From: teamgrumman@aol.com Finally, someone who paying attention. Ring flutter is very rare. Especially at less than 2700 rpm. Piston ring seal depends on a balance of four forces: combustion pressure, ring inertia, the rings radial expansion pressure and crankcase pressure. Ring flutter is uncontrolled oscillation due to an imbalance of those forces. Once a pistons rings go into flutter, their ability to scrape oil off the cylinder wall as the piston moves downward is impaired, blow-by increases and oil consumption rises dramatically. The combination of high rpm and low crankcase pressure typical of low engine loads causes those four forces to become imbalanced. The small amount time the engine sees regular, high-rpm, light-load operation, is rare. Even so, if that happens, you may experience ring flutter and high oil consumption, but not likely. -----Original Message----- From: Kelly McMullen Sent: Wed, 10 Oct 2007 6:43 pm Subject: Re: Engines-List: Ring Flutter? I guess I just don't see how you relate a question about theoretical ring flutter with engine timing or age of fuel. I'm missing the connection. Actually a 180 only requires 91-96 or 91 mogas with STC. Only the 160 and the 200hp versions need the extra octane. On 10/10/07, Gene Smith wrote: I would be concerned...I suggest you check your engine timing...Also if your fuel is old, it has lost some of it's volatility, and I would drain it and replace it with "fresh" gasoline...Are you burning Auto Gas?..The book says that 360 needs 100LL (all of them, 160 and above require it.)....................Good Luck.......................CHEERS!!!!.............................Gene Smith. ----- Original Message ----- From: Fredrick Kerfoot To: engines-list@matronics.com Sent: Wednesday, October 10, 2007 6:37 AM Subject: Engines-List: Ring Flutter? What is piston "Ring Flutter"?? I have an IO360. Just how concerned should I be? Fred K Help yourself to FREE treats served up daily at the Messenger Caf. Stop by today! href="http://www.matronics.com/Navigator?Engines-List"> http://www.matronics.com/Navigator?Engines-List href="http://forums.matronics.com"> http://forums.matronics.com -= the many List utilities such as the Subscriptions page, ronics.com/Navigator?Engines-List" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> http://www.matronics.com/Navigator?Engines-List k" onclick="return top.js.OpenExtLink(window,event,this)"> http://forums.matronics.com ========== ________________________________________________________________________ Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com ________________________________ Message 3 _____________________________________ Time: 08:11:54 PM PST US From: Fiveonepw@aol.com Subject: Engines-List: Knock sensors? We've had knock sensors on cars for many years that retard timing in the event of detonation to keep engines running at peak fuel efficiency. Since it is almost impossible to detect thru conventional aircraft engine instrumentation that I'm aware of, or audibly, (such as in cars) that such a device would be very useful in planes, but I've never heard of such a critter. I'm kinda guessing that it is difficult in an air-cooled engine or because of the large cylinder displacement. Anyone aware of any attempts to do this on Lycs or Conts? 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