X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.4c2o) with ESMTP id 4890638 for flyrotary@lancaironline.net; Fri, 04 Mar 2011 10:12:36 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.1 cv=pepdxKapwHuwCZNFD5uob2wvham6E+RljB0uXw08FdQ= c=1 sm=0 a=81MsLKu5UWQA:10 a=rPkcCx1H5rrOSfN0dPC7kw==:17 a=dqvRKdyRPBwRqD-fqJoA:9 a=Brzn9ZNgZ8F069xvOzIA:7 a=yM7GU0jtHUrUP-NDPG-bhwzj5IwA:4 a=wPNLvfGTeEIA:10 a=glYVDZ00AAAA:8 a=Ia-xEzejAAAA:8 a=HAW3EHHh90OLdOLUDFYA:9 a=hH5Q4KKd6VdZis32WBMA:7 a=U7ItE9tP40DJfurLwFtLo51wPpQA:4 a=XCwpvLtFMdsA:10 a=EzXvWhQp4_cA:10 a=rPkcCx1H5rrOSfN0dPC7kw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.167.5 Received: from [174.110.167.5] ([174.110.167.5:50768] helo=EdPC) by cdptpa-oedge03.mail.rr.com (envelope-from ) (ecelerity 2.2.3.46 r()) with ESMTP id 17/84-19545-141017D4; Fri, 04 Mar 2011 15:12:01 +0000 Message-ID: <8842C8010C9444AFA1D05A4EFAF946F4@EdPC> From: "Ed Anderson" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Knock sensor and indicator Date: Fri, 4 Mar 2011 10:11:49 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000D_01CBDA54.934F8000" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_000D_01CBDA54.934F8000 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Chris, You are about to undertake a project of some magnitude, = regarding a knock sensor. In concept the idea is quite simple, in execution it gets quite complex. = =20 1st if you do not tie it in to some automatic anti-knock method (such as = automatically reducing ignition advance, blowing the waste gate, etc) = that reacts very quickly, your human response to the warning and time to = take action - may be too late to avoid damage. Most systems respond by = reducing ignition advance (probably the fastest thing that can be done). 2nd Separating out the specific frequency (out of all the ongoing engine = noise) that indicates a detonation can be done with a notch filter = providing (important provision) you know that specific knock signal = frequency and magnitude. That generally takes electronic circuits and = sometimes pretty advanced digital filters to separate out the signal = from all the engine noise. =20 If you are bound to pursue this - then the place to start is probably = with the knock sensor system on the Rx7/8. The "microphone" you screw = into the block would probably be a good place to start, but the rest of = the anit-knock system I would hesitate to take on. Even then, the = sound spectrum from a rotary in an automobile installation and that in = an aircraft may be considerably different - so the filter has to be = "tuned" the the noise environment it will function in. Now the old brain can be a pretty sophisticate noise filter and complex = processing unit - I am told, but never tried, that hooking up a knock = sensor microphone to a relatively simply audio frequency type amplifier = - that with Practice, one can learn to distinguished the sound of a = knock. The problem with this approach is two fold as I see it - one, = your engine has to go into detonation in order to train the ear/brain = (the very thing you are trying to avoid) and two, you still have to be = able to recognize it and react quickly enough to prevent damage. =20 There are probably other steps more easily taken to reduce likely hood = of detonation. Like ensuring your static timing is accurately set, = boost levels (if using turbo/super chargers) are kept very modest, = Engine temperatures are kept within bounds, intercooler is used to cool = intake air, etc). =20 But, I certain wish you success and it would undoubtedly be an valuable = addition to the rotary community (especially those flying with forced = inductions systems) body of knowledge and tools. Good Luck Ed From: Chris Barber=20 Sent: Friday, March 04, 2011 9:43 AM To: Rotary motors in aircraft=20 Subject: [FlyRotary] Knock sensor and indicator Since I have had an issue with detonation, I am contemplating adding a = knock sensor. What do y'all know about this addition. I do not believe = Tracy's EM has a provision for a reading, so, what might be a good route = to take. The brief research I have done shows different frequencies, = types etc. What would be correct for a rotary, both as to a sensor and = something to notify me in the cabin? Thanks. I am about to replace ALL = my apex seals and soft parts and hopefully finally lick this = issue....hopefully....did I mention = hopefully...determinably...persistent? (heck, I wasn't planning anything = else this weekend ) Chris ------=_NextPart_000_000D_01CBDA54.934F8000 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Chris, You are about to undertake a project of = some=20 magnitude,  regarding a knock sensor.
 
In concept the idea is quite simple, in = execution it gets=20 quite complex. 
 
1st if you do not tie it in to some automatic = anti-knock=20 method (such as automatically  reducing ignition advance, blowing = the waste=20 gate, etc) that reacts very quickly, your human response to the warning = and time=20 to take action - may be too late to avoid damage.  Most systems = respond by=20 reducing ignition advance (probably the fastest thing that can be=20 done).
 
2nd Separating out the specific frequency (out = of all the=20 ongoing engine noise) that indicates a detonation can be done with a = notch=20 filter providing (important provision) you know that specific knock = signal=20 frequency and magnitude. That  generally takes electronic = circuits and=20 sometimes pretty advanced digital filters to separate out the signal = from all=20 the engine noise. 
 
If you are bound to pursue this - then the place = to start=20 is probably with the knock sensor system on the Rx7/8.  The = "microphone"=20 you screw into the block would probably be a good place to start, but = the rest=20 of the anit-knock system I would hesitate to take on.  Even = then,=20  the sound spectrum from a rotary in an automobile installation and = that in=20 an aircraft may be considerably different - so the filter has to be = "tuned" the=20 the noise environment it will function in.
 
Now the old brain can be a pretty sophisticate = noise=20 filter and complex processing unit - I am told, but never tried, that = hooking=20 up a knock sensor microphone to a relatively simply audio frequency = type=20 amplifier - that with Practice, one can learn to distinguished the sound = of a=20 knock.  The problem with this approach is two fold as I see it - = one, your=20 engine has to go into detonation in order to train the ear/brain (the = very thing=20 you are trying to avoid) and two, you still have to be able to recognize = it and=20 react quickly enough to prevent damage. 
 
There are probably other steps more easily taken = to reduce=20 likely hood of detonation.  Like ensuring your static timing is = accurately=20 set, boost levels (if using turbo/super chargers) are kept very modest, = Engine=20 temperatures are kept within bounds, intercooler is used to cool intake = air,=20 etc). 
 
But, I certain wish you success and it would = undoubtedly=20 be an valuable addition to the rotary community (especially those flying = with=20 forced inductions systems) body of knowledge and tools.
 
Good Luck
 
Ed

Sent: Friday, March 04, 2011 9:43 AM
Subject: [FlyRotary] Knock sensor and = indicator

Since I have had an issue with detonation, I = am contemplating=20 adding a knock sensor.  What do y'all know about this = addition.  I do=20 not believe Tracy's EM has a = provision=20 for a reading, so, what might be a good route to take.  The brief = research=20 I have done shows different frequencies, types etc.   = What=20 would be correct for a rotary, both as to a sensor and something=20 to notify me in the cabin?  Thanks.  I am about to = replace ALL my apex seals and soft parts and hopefully finally lick = this=20 issue....hopefully....did I mention=20 hopefully...determinably...persistent? (heck, I wasn't = planning=20 anything else this weekend <g>)

 

Chris

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