Today's Message Index:
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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
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| Subject: | 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" <VE3LVO@rac.ca>
> 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
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| Subject: | 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" <VE3LVO@rac.ca>
>> 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
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| Subject: | 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
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| Subject: | Re: 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
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| Subject: | Re: corvair engine |
thanks.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=139830#139830
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