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That’s just not fair. And honestly I don’t understand
how it worked so well for you without any tuning required at all. On completely
different engines. Mine was a bear to get right. In fact never really did
get it completely right, but close enough to fly safely. Then I pulled the
wrecking yard injectors and installed my overhauled injectors hoping to get more
balanced egts across the full rpm range. With the replacement injectors, more
tuning required. But unlike a carb at least its easy to tune in real
time.
Mike Wills
Sent: Sunday, April 25, 2010 11:29 AM
Subject: [FlyRotary] Re: getting lost in the tuning
process
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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