---------------------------------------------------------- Engines-List Digest Archive --- Total Messages Posted Sat 10/13/07: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:37 AM - Re: Engines-List Digest: 14 Msgs - 10/12/07 (Gary Casey) 2. 05:37 AM - Re: Ring flutter? (Gary Casey) 3. 05:40 AM - Re: Knock sensors? (Gary Casey) 4. 06:51 PM - Re: Knock sensors (AzevedoFlyer@aol.com) 5. 07:07 PM - Re: corvair engine (SockPuppet61) ________________________________ Message 1 _____________________________________ Time: 05:37:31 AM PST US From: Gary Casey Subject: Engines-List: Re: Engines-List Digest: 14 Msgs - 10/12/07 I've heard this before, but consider this: The piston rings run at no load half the time regardless of manifold pressure (BMEP). During the exhaust and intake strokes the pressure is very low, so if the rings were going to flutter why don't they do it then? Gary > > Time: 06:37:28 AM PST US > From: "Fergus Kyle" > Subject: Engines-List: Ring flutter? > > > Piston Ring flutter: > `....seems to me we had the same problem on the Super Connie (Old > Bob may comment here). This aircraft was named the largest 3-engined > airliner on the Atlantic. So. on pain of death no Driver, Airframe, > would > ever reduce the Brake Mean Effective Pressure (BMEP) below 90 with > the RPM > at cruise or descent because the condition would induce 'ring > flutter' and > an earlier engine change was inevitable. > I suspect my employer's profit was based more on engine changes than > seat mileage. > Cheers, Ferg ________________________________ Message 2 _____________________________________ Time: 05:37:58 AM PST US From: Gary Casey Subject: Engines-List: Re: Ring flutter? On Oct 13, 2007, at 5:27 AM, Gary Casey wrote: > I've heard this before, but consider this: The piston rings run at > no load half the time regardless of manifold pressure (BMEP). > During the exhaust and intake strokes the pressure is very low, so > if the rings were going to flutter why don't they do it then? > Gary > >> >> Time: 06:37:28 AM PST US >> From: "Fergus Kyle" >> Subject: Engines-List: Ring flutter? >> >> >> Piston Ring flutter: >> `....seems to me we had the same problem on the Super Connie (Old >> Bob may comment here). This aircraft was named the largest 3-engined >> airliner on the Atlantic. So. on pain of death no Driver, >> Airframe, would >> ever reduce the Brake Mean Effective Pressure (BMEP) below 90 with >> the RPM >> at cruise or descent because the condition would induce 'ring >> flutter' and >> an earlier engine change was inevitable. >> I suspect my employer's profit was based more on engine changes than >> seat mileage. >> Cheers, Ferg > ________________________________ Message 3 _____________________________________ Time: 05:40:55 AM PST US From: Gary Casey Subject: Engines-List: Re: Knock sensors? I suspect you are right - the market is very, very small. The knock sensor itself usually is tuned to respond to the knock frequency of a particular engine and the frequency of a large-bore aircraft engine is almost certainly a lot different than a car engine, preventing the use of a cheap readily available sensor. Any knock control system is software-intensive, with the algorithm being carefully worked out during lots of experimentation (running on the dyno for lots of hours). At high power settings the knock is often undetectable as it is drowned out by the other noises (the car engine systems that I was familiar with years ago essentially shut off at high load and relied on the timing acquired during light load operation). And then the real kicker is that on an aircraft system you want some kind of fault tolerance - how do you protect against some fault in the system that over-advances the spark? What do you use to check it? The combination of all these things will, in my opinion, prevent the use of a vibration-based knock system in an aircraft engine for some time. The optical system is perhaps a different matter. Gary Casey > > Time: 06:26:19 PM PST US > Subject: Re: Engines-List: Knock sensors? > From: azevedoflyer@aol.com > > > Maybe we should try again! > Piston slap is a repeatable, rpm-correlated event. Detonation has a > high frequency > and fast-decaying "signature". Can be easily tracked and filtered. > Never had > problems with these two. Aircooled engines complicate things a bit > because > of the finning which radiate vibration in a very ample spectrum. > Despite the apparent > complexity, I am sure someone can develop a reliable knock sensor for > aircooled engines. What about PORSCHE engines? > The problem might reside more in the lack of a large enough market > for such product > than anything else. ________________________________ Message 4 _____________________________________ Time: 06:51:36 PM PST US From: AzevedoFlyer@aol.com Subject: Re: Engines-List: Knock sensors Dean and All, No question that an electronic means of knock detection is the preferred route, given its sensitivity and ease of integration to the electronic ECU. For altogether different reasons, I developed (...and have a Form 337 granted by FAA) what I call an Engine Health Monitor Indicator (EHMI) and have it in my instrument panel. Among several other factors, detonation beyond light (light as defined as a ping or two here and there or continuous, barely audible in a test cell) will cause ring flutter. Flutter will change blowby emission. The EHMI monitors (passively) the blowby emitted. On a modified meter, there are bands colored Green / Yellow and Red. During take off you have the worst condition in which detonation could become a problem. That sets your upper limit of your Green band. If, at any time, you see a trend towards this upper value, for sure something is steadily deteriorating and you should do something about it regardless of the source. You know it is affecting your PCU (power cylinder unit), so its bad news. The great thing about monitoring BBY is that it is the first variable to indicate something going wrong. For example, our engines are prone to ring and valve sticking. If a ring is intermittently stuck in its groove, not even JPI exhaust temperature indicators will catch it, as exhaust temps will remain the same. But the BBY will be affected...and EHMI will catch it! I've been flying with this indicator in my plane for the last two years. I can tell when oil reaches the upper parts of the cylinder after a cold, long inactivity. I can tell when oil has reached an ideal operating temperature. I can use it as a leaning indication instrument. I can tell if a plug has shorted or I left mags on Left or Right and not in BOTH. I can distinguish between Left and Right mags firing. I can...(still learning...) The guys at the local FAA FISDO were sufficiently impressed to say "...you have turned $4-$5K instruments out there obsolete! Yours should be a required instrument in every new piston engined plane". Felt complimented! Anyway, this is not a commercial/propaganda email. Purpose is to say that if we satisfy ourselves with less than perfection, something can be done on the cheap to improve engine health monitiring. Sorry for the lengthy mail. Just got carried away I guess. Miguel PA22/20-150 N8714D ________________________________ Message 5 _____________________________________ Time: 07:07:27 PM PST US Subject: Engines-List: Re: corvair engine From: "SockPuppet61" thanks. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=139830#139830 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message engines-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Engines-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/engines-list Browse Digests http://www.matronics.com/digest/engines-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.