From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: EC Staging Point
Date: Thu, 18 Jun 2020 06:30:32 +0800
References: <list-382330@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-382330@logan.com>
Message-Id: <A80D6B71-CAC1-435B-8CFB-C1B27E49294E@gmail.com>

Hi Steve Boese


In my recent experience (staging MAP set at just below 20=E2=80=9D) it =
looks like the Pri injectors were saturated and causing my grief.
My gut was telling me it was about satuated Primaries.
I=E2=80=99ll lower this down and use your procedure and see how I go.

Thanks so much for providing this detail.
So helpful to have your expertise on here Steve.

Cheers

Steve Izett


> On 18 Jun 2020, at 3:57 am, Steven W. Boese SBoese@uwyo.edu =
<flyrotary@lancaironline.net> wrote:
>=20
> The procedure for tuning that I outlined was not based on staging MAP =
particularly.  The staging MAP can be set to any reasonable value that =
avoids the primary injectors going into saturation.  15.5" Hg would be =
fine.
>=20
> The attached image shows injector and CAS signals from one of my EC2 =
controllers connected to a 13B CAS.  I have two EC2's and they behave =
the same.  The captured signals show operation with primary injectors =
saturated, followed by primary injectors at close to the maximum pulse =
width the EC2 allows before saturation, followed by the stage transition =
to using both the primary and the secondary injectors.  These changes =
all occurred in 5 revolutions of the engine at about 6200 RPM.  The EC2 =
modes were at default values which assumes that the primary and =
secondary fuel injectors are all the same size.
>=20
> It is useful to note the % fuel flow relative that produced at 9 ms =
pulse width which is near the maximum and is indicated by the labels at =
the top of the image.  When the primary injectors have been in =
saturation for 2 revolutions, the fuel flow is 114% of that at 9 ms PW.  =
If the primary injectors had been continuously saturated, the fuel flow =
would have been 124% of that at 9 ms PW.  The result is that the mixture =
will go richer when the primary injectors saturate until increasing fuel =
demand exceeds the saturated fuel flow rate at which time the mixture =
will become leaner.
>=20
> Note also that the fuel flow from both the primary and secondary =
injectors is 87% of the fuel flow from just the primary injectors below =
the staging MAP.  At staging the EC2 simply divides the PW in half and =
does not take into account the 1.2 ms dead time or lag of these =
injectors.  The PW and the actual injector open times are indicated in =
the labels.  The result is the shorter PW above the staging MAP makes =
the injectors behave as if they became smaller since the dead time is =
now a larger fraction of the PW.
>=20
> This demonstrates the difficulty encountered when trying to tune the =
system by the method in the EC2 manual.  The sudden mixture change from =
one table location to the adjacent one when staging takes place is to be =
accomplished by manually making changes to the table values in these =
locations.  Successfully adjusting the table values from the control =
panel requires a stable condition with the MAP at the exact value =
corresponding to the table location to be changed.  This stable =
condition is unlikely to be achieved when the engine has just undergone =
a significant mixture change.
>=20
> Setting mode 3 just below the staging MAP and setting mode 6 just =
above the staging MAP is a work-around for the EC2 not compensating for =
the injector dead time.  Mode 6 was intended to aid tuning when primary =
and secondary injectors of different flow rates were used.  The =
effective flow rate of the injectors changes as a result of staging as =
explained above.  Mode 6 now takes care of this regardless of the =
relative size of the primary and secondary injectors.  The mode 3 or 6 =
adjustment does not have to take place with the MAP corresponding to =
adjacent staging table locations.  After the initial adjustment, one can =
even change the staging MAP within reason without having to make =
adjustments to the table.  The EC2 handles that change fine.
>=20
> I do not know if later EC2 or EC3 controllers incorporate dead time =
compensation.  For those with access to the code, this can be verified =
and if not, the dead time of the injectors in use (usually in the range =
of 0.8 to 1.2 ms) can simply be added in a line of code to the PW =
determined by a controller which doesn't have dead time compensation.  =
Proof of concept of this approach has been demonstrated by adding 1.2 ms =
to the PW of my controllers with hardware between the controller and the =
injector.  The result was much easier tuning equivalent to the =
alternative procedure outlined above.
>=20
> As a point of possible interest, my take on the history of the EC2 =
development follows:  The early EC2's used  diodes to clamp the voltage =
spikes to one diode voltage drop above the power supply (~14V) when the =
injector is turned off.  This gave a path for current to flow from the =
collapsing injector field which delayed the closing of the injector.  =
This delay was similar to the injector dead time and largely avoided the =
mixture going lean (engine bog) upon staging.  There was a difficulty in =
achieving a good idle, however, since very small injector open times =
could not be attained if the delay on closing was too long.  This was =
addressed by replacing the diodes with a device which still clamped the =
voltage but at a higher value.  This minimized the injector closing =
delay and improved the idle tuning characteristics, but the leaning =
(engine bog) upon staging then became an issue due to the uncompensated =
injector dead time.  Two methods for dealing with this have been =
presented above.  Personally, I observed arcing in the relays when =
switching between the A and B controllers with the higher voltage =
clamping setup.  I didn't like the RF noise from the arcing in close =
proximity to the controller processor possibly corrupting the controller =
operation or memory.  So I installed classic RC snubbers in my =
controllers which appears to have eliminated both the arcing and the =
injector closing delay.  This discussion is in no way meant to be =
critical of Tracy's work, but rather as simply indicative of a work in =
progress. =20
>    =20
> Steve Boese
>=20
>=20
>     =20
>=20
>=20
>=20
> =20
>=20
> From: Rotary motors in aircraft <flyrotary@lancaironline.net> on =
behalf of Stephen Izett =
stephen.izett@gmail.com<flyrotary@lancaironline.net>
> Sent: Monday, June 15, 2020 5:26 PM
> To: Rotary motors in aircraft <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Re: EC Staging Point
> =20
> =E2=97=86 This message was sent from a non-UWYO address. Please =
exercise caution when clicking links or opening attachments from =
external sources.
>=20
>=20
> So a couple of things off note:
> 1. Steve Boese' procedure for Mode #3 Inj Floe Rate is below staging =
whereas Tracy=E2=80=99s is above.
> 2. Staging point was set at near 20=E2=80=9D and with the Renesis 4 =
ports smaller Primaries this does seem a bit high.
>         This makes sense of her going lean prior to the secondaries =
kicking in.
> Thanks
>=20
> Steve Izett
>=20
>=20
> > On 16 Jun 2020, at 5:57 am, Stephen Izett stephen.izett@gmail.com =
<flyrotary@lancaironline.net> wrote:
> >
> > Thanks Jeff for finding this. Much appreciated.
> > Steve
>=20
> <injector saturation and stage.jpg>--
> Homepage:  http://www.flyrotary.com/
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