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If I may relate my own recent experience with the tuning process...
There are two systems that I have been working with. One is my flying RV6A with a 1986 13B NA with 4 stock peak and hold (low resistance) fuel injectors, stock CAS, an intake manifold with no intentional dynamic
tuning, and GM ignition coils. The other is a test stand with a 1987 13B NA with 4 stock saturated (high resistance) fuel injectors, stock CAS, also with GM ignition coils. The propellers are quite similar although of different manufacturers. Both systems
have EC2's with chips that were updated early in 2010.
After installing the updated chips in the plane's EC2, I made sure that I had studied the latest copy of the installation manual. I also had the IPAQ EC2 recording system described elsewhere set up to document my
tuning steps so I could review it after the fact to assure myself that I had done things in a reasonable fashion. Starting with the default settings in the EC2, I found to my great dissapointment ;) that no changes in the default settings were needed. I
could use just the manual mixture control to run from rich of peak to lean of peak EGT at any throttle setting available. Max MAP for my location with a field elveation of 7200 ft is always near 23 inches of Hg. A couple of days ago, I flew from home (Laramie,
WY) to Benson, MN at altitudes ranging from 12000 ft to 1300 ft and OAT's ranging from the 20's to 60's, with those default EC2 settings and using the manual mixture control to select the desired operating conditions. There wasn't any hint of an improvement
to be gained from tuning the power plant any differently.
The engine stand which we took to the Contact Magazine fly-in last month has performed similarly. No change from the default settings has been required using either the stock automotive intake system with the dynamic
chamber or a second intake system that I got with the engine. This second intake system has secondary runners controlled by the double butterfly of a cut down stock throttle body and primary runners controlled by the single butterfly of that throttle body.
There is no pneumatic connection between the primary and secondary runners except for MAP sensing lines tee'd together and going to the EC2. There is a mechanical linkage on the throttle body between the primary butterfly and and the double butterfly, of
course. I tested this manifold just because it was available, thinking that there was no way this would work very well. It performed very nearly as well as the stock dynamic chamber, again with the default EC2 settings.
Probably, the the important thing that these systems have in common are the 4 stock fuel injectors all of the same flow characteristics.
Personally, it has been most useful (if I set the staging point different than default) to set the staging point to a setting such that the two primary injectors are used to as high a MAP as possible without them
limiting the fuel flow at about 80% duty cycle. I do this because there is a lower limit to the amount of fuel that the injectors can deliver reliably. This lower limit occurs at about 1.5 to 2 ms pulse width with the injectors I have tested. Below this
limit, the amount of fuel delivered is more a function of the injector dynamics than it is a function of what the EC2 is requesting of it. If the staging point is set too low, one is just getting into the range where the two injectors are working predictably
and then the system switches to using 4 injectors, each one trying to deliver fuel in such small amounts that they are somewhat unpredictable. The dynamic range adjustment in the EC2 may be able to compensate for the low flow non-linearity to some extent,
but it seems to me that this would be most useful to obtain good idle characteristics with two injectors rather than using 4 injectors at relatively low but non-idle power settings. Setting the staging point to a low MAP may be useful as an exercise in learning
the steps involved in tuning the EC2 while avoid cooling porblems on the ground, but I suspect that it will be frustrating if the resulting parameters are expected to work well in flight. It seems to me that it will be much more productive to temporarily
resolve the ground cooling issue and program the EC2 under conditions as close to the power levels that would be encountered in flight as possible.
Please note that these are just my thoughts based on the special cases I have to work with and there is absolutely no criticism intended toward anyone. This email may also be the result of being
away from home on a gloomy day unfit for flying.
Steve Boese
From: Rotary motors in aircraft [flyrotary@lancaironline.net] On Behalf Of Bill Bradburry [bbradburry@bellsouth.net]
Sent: Sunday, April 25, 2010 7:41 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: getting lost in the tuning process
You certainly have it right about the better understanding part! :>)
So, since it has no effect, why, in step 1, do you say, “with the engine running below the staging point, select mode 6 and turn the
program knob slightly to the left of the 12:00 oclock position and press the program store switch”???
Is this some kind of arming step??
The mixture is really rich before I start this step. I have the mixture control knob at probably 9:00 oclock on both sides of 15” of
map. Is this going to have an effect on that? Or is it just in case the mixture changes when you go from below 15 to above 15?
With the 4 yellow injectors, where do you recommend the staging point be set? I have it set now at 15 mostly so I can do stuff like
this without running at high power and causing ground cooling problems. If I get every thing set and then later change the staging point, will this cause a need for a do over?
I will clear and start over. When would be a good time to call if need be?
Thanks for the response that helps to clear it up.
By the way, to those carb guys, this is a little confusing, but no way bad enough to justify going with a carburetor!!!
Bill B
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