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From: "George Lendich" <lendich@aanet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-3636649@logan.com>
Subject: Re: [FlyRotary] Re: Pulses Per Rev and the TACH: [FlyRotary] Re: John Downings Tach
Date: Sat, 9 May 2009 09:51:13 +1000
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> 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.
Bob,
Don't we all!
George (down under)