Received-SPF: softfail
 receiver=logan.com; client-ip=64.102.122.148; envelope-from=echristley@nc.rr.com
Message-ID: <47AB1841.8010204@nc.rr.com>
Date: Thu, 07 Feb 2008 09:40:01 -0500
From: Ernest Christley <echristley@nc.rr.com>
Reply-To: echristley@nc.rr.com
User-Agent: Thunderbird 2.0.0.6 (X11/20071022)
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Hardwire? [FlyRotary] Re: Ignition advance
References: <list-2719290@logan.com>
In-Reply-To: <list-2719290@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Ed Anderson wrote:
> Ernest, not familiar with your EFI system.  However, your statement 
> about hardwiring it for 20 deg and then using the computer to add 
> advance caught my attention - normally that  is not how it is done.  
> It is difficult for a CPU design to "ADD" or advance ignition timing 
> from a static timing point as that implies it has to know in advance 
> (precognition but not pre-ignition - sorry, couldn't help it)  when 
> the next firing event is coming.  All of the EFI units  that I am 
> familiar will  set or "Hardwire" the static timing to the maximum 
> amount of ignition timing advance they will ever want.  Then the 
> computer is used to retard the timing from that point which is much 
> easier to do.  Tracy's EC2 uses this method and that is why his 
> instruction have you set the static ignition timing to 31-35 Deg BTDC 
> and then the CPU simply backs off to there to the "Advance" you want.
>
> FWIW
>
> Ed
http://www.megamanual.com/ms2/EDIS.htm

There is no way I can explain it any better than this.  My understanding 
is that for the EDIS system there is a basic advance set by the physical 
alignment of the parts.  That advance is then increased by a controlling 
computer with the SAW signal. 

There is precognition of sorts.  Because of the missing tooth, the 
controller knows when the cylinder is coming up to TDC.