X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from EXHUB003-4.exch003intermedia.net ([207.5.74.111] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTPS id 3638701 for flyrotary@lancaironline.net; Mon, 11 May 2009 12:45:41 -0400 Received-SPF: none receiver=logan.com; client-ip=207.5.74.111; envelope-from=jwhaley@datacast.com Received: from EXVMBX003-5.exch003intermedia.net ([207.5.74.45]) by EXHUB003-4.exch003intermedia.net ([207.5.74.111]) with mapi; Mon, 11 May 2009 09:45:05 -0700 From: Jeff Whaley To: Rotary motors in aircraft Date: Mon, 11 May 2009 09:45:04 -0700 Subject: RE: [FlyRotary] Re: Pulses Per Rev and the TACH: [FlyRotary] Re: John Downings Tach Thread-Topic: [FlyRotary] Re: Pulses Per Rev and the TACH: [FlyRotary] Re: John Downings Tach Thread-Index: AcnQMSpiEsvcipraRHum70ulUoUlVQCI6JOg Message-ID: References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Hi Bob, Ed, sorry for the late reply but this is my work email, so I'm not = active on the list during weekends. I'm on my lunch hour ... anyway, yes the 2 pulses per 720 degrees is correc= t and not 2 pulses per 360; the rest of my explanation about the UMA was co= rrect. It will not work properly with 2 spark plug pick-ups on a 6-cyl but = it should work just fine if connected to the Leading plugs of each rotor on= the rotary. The digital UMA conditions the spark plug pulses then drives a= 555 timer circuit creating a much more uniform pulse train, the pulse trai= n is then sent to a frequency-to-voltage convertor. So for a 4/4 or a 2/2 t= he f-to-v convertor should see 2 equally spaced pulses every 720 degrees bu= t if tapping 2:6 cylinders the spacing will no longer be uniform which tran= slates to a lower frequency, a lower voltage and a display error. Jeff -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Beh= alf Of Bob White Sent: Friday, May 08, 2009 7:00 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Pulses Per Rev and the TACH: [FlyRotary] Re: John = Downings Tach Hi Ed, "if you are just tapping one spark plug you would get 1 spark per 360 deg." I'm not quite convinced of that. Every piston fires once every 720 deg. Compression/(fire plug)/power stroke is 360, then exhaust/intake is a second 360. If I sample one plug I will see one spark for 720. From Jeff's explanation, the tach mentioned samples two spark plug wires for a 4 cylinder 4 stroke (although I think this is 1 pulse per 360 rather than 2). For a two stroke, only one plug is sampled, so still 1 pulse per 360. At least I think that's what I understood Jeff to be saying. On a 4/4 engine, the tach's that work with a coil and distributor will see two pulses per 360 as two cylinders will fire in one 360 and the other two in the next 360. If I still have this wrong, then I need more help! :) Bob W. On Fri, 8 May 2009 16:32:20 -0400 "Ed Anderson" wrote: > Hi Bob, >=20 > A four cylinder four stroke fires all four cylinders in 720 deg or two > cylinders each 360 deg (as you know). Therefore, normally if you are jus= t > tapping one spark plug you would get 1 spark per 360 deg. However, most > (but not all) tachs expect two pulses per 360 deg (frequently referred t= o > as 2 PPR (pulses per revolution -360 deg). So if your tach is expecting = two > per rev and is only getting one pulse per rev, then the period between > pulses is twice as long as what it is expecting and therefore it will > generally indicate 1/2 of the actually rpm (if its only get one pulse per > rev and is set up for 2 PPR). Now on some tachs you can set the PPR from= 1 > to a large number, but for most of the ones we use its generally 2, 3 or = 4 > for 4, 6 and 8 cylinder engines. >=20 > A two stroke two cylinder fires both cylinders each 360 deg instead of 72= 0 > of the four stroke - therefore you get 2 PPR for the two cylinder two str= oke > exactly like you get for 4 cylinders on the four stroke for 360 deg. So = a 2 > cylinder 2 stroke and a 4 cylinder 4 stroke will read the same RPM. At > least that is how I recall it works. >=20 > Ed >=20 > Ed Anderson >=20 > Rv-6A N494BW Rotary Powered >=20 > Matthews, NC >=20 > eanderson@carolina.rr.com >=20 > http://www.andersonee.com >=20 > http://www.dmack.net/mazda/index.html >=20 > http://www.flyrotary.com/ >=20 > http://members.cox.net/rogersda/rotary/configs.htm#N494BW >=20 > http://www.rotaryaviation.com/Rotorhead%20Truth.htm >=20 > -----Original Message----- > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On > Behalf Of Bob White > Sent: Friday, May 08, 2009 12:18 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] Re: John Downings Tach >=20 > Hi Jeff, >=20 > Thanks for the tip. There is something I don't understand about the > specs for this unit. It's good for 4 cylinder 4 stroke or 2 cylinder 2 > stroke. If I use the spark plug wire for the pickup, a 4 stroke > (piston) engine will see one spark per two rev. Why does it matter how > many pistons there are? If it's a wasted spark system, then one spark > per rev. just like a two stroke piston engine. There must be something > basic I don't understand. What sort of mod did it need for the V6? >=20 > BTW, what is the maximum rpm reading for that unit? >=20 > Thanks, > Bob W. >=20 > On Fri, 8 May 2009 07:48:47 -0700 > Jeff Whaley wrote: >=20 > > I like the belt and suspenders!! > > I am using a UMA digital tachometer 2 1/4" from Aircraft Spruce that wa= s > originally designed for 4 cylinder engines using an electrical impulse > pickup from spark plug leads. I modified it to mate with the Ford V6; I h= ave > modified it again to connect to the EC2 driving the R1 PRI injector. The > rotary firing system is similar to a 4 cylinder so if this tach is still > available (Part # 10-24885) it would work off spark plug impulse couplers= . > > Jeff > >=20 > > -----Original Message----- > > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On > Behalf Of Bob White > > Sent: Friday, May 08, 2009 12:14 AM > > To: Rotary motors in aircraft > > Subject: [FlyRotary] John Downings Tach > >=20 > > John is using a standard tach that is normally connected to a > distributor/coil ignition system. The straight 12V pulse used for the > > LS1 coils wouldn't activate it. I built an interface for him that > involved taking that pulse as an input and generating a shorter constant > pulse width output. I modified the tach to trigger on the lower voltage > signal, and adjusted the scale factor to read correctly with one pulse/re= v. > As John reported, it worked for about 0.8 hours, then quit. He is sendin= g > everything back to me so that I can find out where the problem is. I wou= ld > like to find a tach solution that John can use without modifying anything= . > The parameters are he has a 2 1/16 inch mounting hole, the tach needs to > read correctly with 1 pulse/rev (would be the same as a two cylinder pist= on > engine with coil and distributor), should trigger directly on a 12V pulse= . > >=20 > > I've found tachs on the web that mention working with distributorless o= r > electronic systems, but none of them were the 2 1/16 inch type. I found = a > converter, the MSD 8913, but on the Summit Racing catalog it specifically > says it won't work with the LS-1 system. It work by sensing the current > pulses to the 12V power lead on the coil. I don't know why it wouldn't w= ork > with an LS-1 coil, but it doesn't seem like a good investment when the LS= -1 > is specifically mentioned as not working. > >=20 > > Can anyone recommend a tach solution that John can use with his LS-1 Co= il > rotary engine combination? > >=20 > > On another topic, John has the only system I've heard of that has the > capability to run on either EFI or a carburettor. John posted a picture = of > his Tailwind a few days ago. It's a very good picture but considering th= e > redundancy of the EFI/carb system, I felt that the picture was lacking. = I > submit this edited version as being more indicative of John's desire for > uncompromised safety. > >=20 > > Bob W. > >=20 > > -- > > N93BD - Rotary Powered BD-4 - http://www.bob-white.com > > 3.8 Hours Total Time and holding > > Cables for your rotary installation - http://roblinstores.com/ > >=20 > > -- > > Homepage: http://www.flyrotary.com/ > > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html >=20 >=20 --=20 N93BD - Rotary Powered BD-4 - http://www.bob-white.com 3.8 Hours Total Time and holding Cables for your rotary installation - http://roblinstores.com/ -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.= html