Steve:

Yes, excellent work and report.

I understand the part about random EC2 dwell times during starting causing the weak or non-existent spark but I’m not 100% clear on the relationship to Mode 8 timing retard and the overall ignition timing result at cruise or WOT settings. Your conclusion states: “ A mode 8 setting of 10 degrees retarded is used for starting. Desired ignition timing is achieved by setting the CAS physical position in the engine block to compensate for this.”

Does this mean that the standard mechanical setting of 35 BTDC should be changed to 45 BTDC to compensate for the Mode 8, 10 degree retard?

What was the net ignition timing at high rpm result from this experiment?

 

If I understand the EC2 timing correctly, once you set it to +/- zero it affects the entire operating range.  A retarded timing would definitely improve starting and low idle but you have now also limited the maximum advance at cruise or WOT.  It would be great if the EC2 could have 2 timing settings based on rpm, similar to the 2 MAP ranges of below and above staging.

Jeff

 

 

 

Steve;

 

You are to be commended for some very scholarly work, and excellent reporting.  There are many hours invested there, as well as expenses for equipment.

 

For nearly 2 years now I have been puzzled by my observation of spark conditions during cranking that are consistent with your findings.  Since my engine has always started, and run well, I didn't have motivation to pursue the causes.  It may also be at least part of the explanation for the inability to get smooth operation below 1200 rpm.

 

Of course my EC2 has been updated since, so I don’t know if the behavior is still the same.

 

Coincidentally, just this past week I have done some further tests of timing adjustment.  You my recall from my dyno report that the timing of my engine as I received it was way off because of the use of a 12A front cover (and pointer) on the 20B engine.  We set the CAS position based on estimated TDC by observing the tip seals between the leading and trailing plug holes.  During the testing we verified the timing based on a trace from a pressure transducer in a trailing plug hole; and decided that about -2 steps on the EC2 it 'looked right'.  I've been running that way since (and the 2 steps retarded may have been a plus as far as starting spark is concerned).

 

Some time back I had varied the timing a couple of steps during static runup; and could not discern a difference, so I left it as is.  I haven’t bothered with in-flight variation, partly because I was a bit hesitant to be changing it during flight. I finally did so at lean cruise conditions, and found that about 3 more steps retarding made a discernable increase in rpm (5450 to 5500).  So my EC2 is now set at -10 degrees from default.  I haven’t yet made any further spark checks, or even observed if low idle is any smoother.

 

I may retard a bit on the CAS, and then do some more observation to see if there is an ‘optimum’.  Then set one of the controllers 5 steps retarded for use in starting.

 

I guess you have now added to Tracy’s TTD list to figure out what, if anything, should be done as a result.

 

Al

 

 

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of sboese
Sent: Wednesday, December 09, 2009 2:30 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] EC2 signals

 

Steve, Al and others who may be interested in EC2 ignition characteristics,

 

I have added a page to the http://www.rotarycopilot.com/ website which is an

attempt to show why I choose to use a 10 degree retarded mode 8 ignition

timing setting.  This setting is beneficial for startup and very slow idle

with my EC2's. 

The previously mentioned download to this information has been removed from

the website's downloads page.  Now the information can be viewed directly

without having to download, unzip, and open the html file.

With the version of Internet Explorer I have, it is possible to click on an

image from the web site page and download the original if a clearer image is

desired.

 

Steve Boese

   

 

 

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