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From: "Al Gietzen" <ALVentures@cox.net>
To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
Subject: MAP pulses (20B)
Date: Sat, 2 Oct 2004 09:38:59 -0700
Message-ID: <000001c4a89e$51724940$6400a8c0@BigAl>
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For those of us that are using TWM throttle bodies, or similar =
configuration
with individual throttle plates for each runner and MAP ports =
downstream;
MAP sensing is a different ball game.  For both the ECU or MP referenced
fuel pressure regulators, pulse filtering is required for proper =
operation,
especially toward the low end of rpm and power.  If you don't have this
configuration, you can stop here.

=20

We have already determined that some means of pulse damping was =
necessary
with Tracy's ECU for smooth running below about 2000 rpm.  I had =
initially
just added some volume using a section of bigger hose, which helped
considerable, but wanted to do some further work to try and decide how =
best
to set it up.

=20

This week I installed a dial type fuel pressure gauge to use to =
calibrate
the EM2.  With engine off, running one fuel pump gave a nice steady =
reading
of 42 psi, and both pumps gave 43.5; which is the 3-bar setting that TWM
said to expect.  What surprised me was that with the engine running at =
2000,
the pointer was swinging very rapidly over a range of over a pretty wide
range; from about 27 to 37 psi.  It is an undamped bourdon-tube gauge,
responding to a lot of pulsing.  I had no pulse filtering between the
manifold and the fuel pressure regulator.

=20

I also was noting that at a fixed throttle setting the MAP pressure =
readout
on EM2 was varying over about 1" with the different samplings.  Long =
story
short; after some modeling, I started on the side of too much damping.  =
I
now have a bit over 2 cu. in. of volume in the line from the MAP ports =
(the
ports from each of the three runners connected together), then a 0.025"
orifice restrictor, and then a T that goes to the EC2 and back to the FP
regulator (about 1 cu. in. volume).  The fuel pressure gauge is now =
quite
steady at about 32 psi for those same conditions; and the MAP readout is
steady.

=20

The volume downstream from the orifice (to the EC2 and the FP regulator) =
is
now a bit too large making the response too slow.  Its fine for the =
normal
slow power changes, but I noted that pulling the throttle rapidly back =
to
idle results in a dead spot while the mixture is too rich (MAP decaying =
too
slowly).  The response can be varied by varying the volume downstream =
from
the orifice, or changing the orifice diameter.  I intend to reduce the
volume I have in the line to the EC2.

=20

If you want to think about it, consider the volume in the line as a =
spring
(linear with force, more volume =3D weaker spring), and the restrictor =
as a
hydraulic damper (flow varying with about the cube root of the force; I
think; smaller diameter =3D more damping).  Best not to think about it =
too
hard, cuz it's not that critical.

=20

Al

=20

=20


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<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>For those of us that are using =
TWM
throttle bodies, or similar configuration with individual throttle =
plates for
each runner and MAP ports downstream; MAP sensing is a different ball
game.&nbsp; For both the ECU or MP referenced fuel pressure regulators, =
pulse
filtering is required for proper operation, especially toward the low =
end of
rpm and power.&nbsp; If you don&#8217;t have this configuration, you can =
stop
here.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>We have already determined that =
some
means of pulse damping was necessary with </span></font><font size=3D2
  color=3Dblue face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;
  color:blue'>Tracy</span></font><font size=3D2 color=3Dblue =
face=3DVerdana><span
style=3D'font-size:11.0pt;font-family:Verdana;color:blue'>&#8217;s ECU =
for smooth
running below about 2000 rpm.&nbsp; I had initially just added some =
volume
using a section of bigger hose, which helped considerable, but wanted to =
do
some further work to try and decide how best to set it =
up.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>This week I installed a dial type =
fuel pressure
gauge to use to calibrate the EM2. &nbsp;With engine off, running one =
fuel pump
gave a nice steady reading of 42 psi, and both pumps gave 43.5; which is =
the
3-bar setting that TWM said to expect.&nbsp; What surprised me was that =
with
the engine running at 2000, the pointer was swinging very rapidly over a =
range
of over a pretty wide range; from about 27 to 37 psi.&nbsp; It is an =
undamped
bourdon-tube gauge, responding to a lot of pulsing.&nbsp; I had no pulse
filtering between the manifold and the fuel pressure =
regulator.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>I also was noting that at a fixed
throttle setting the MAP pressure readout on EM2 was varying over about =
1&#8221;
with the different samplings. &nbsp;Long story short; after some =
modeling, I
started on the side of too much damping.&nbsp; I now have a bit over 2 =
cu. in.
of volume in the line from the MAP ports (the ports from each of the =
three
runners connected together), then a 0.025&#8221; orifice restrictor, and =
then a
T that goes to the EC2 and back to the FP regulator (about 1 cu. in. =
volume).&nbsp;
The fuel pressure gauge is now quite steady at about 32 psi for those =
same
conditions; and the MAP readout is steady.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>The volume downstream from the =
orifice
(to the EC2 and the FP regulator) is now a bit too large making the =
response
too slow.&nbsp; Its fine for the normal slow power changes, but I noted =
that
pulling the throttle rapidly back to idle results in a dead spot while =
the
mixture is too rich (MAP decaying too slowly).&nbsp; The response can be =
varied
by varying the volume downstream from the orifice, or changing the =
orifice
diameter.&nbsp; I intend to reduce the volume I have in the line to the =
EC2.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>If you want to think about it, =
consider
the volume in the line as a spring (linear with force, more volume =3D =
weaker
spring), and the restrictor as a hydraulic damper (flow varying with =
about the
cube root of the force; I think; smaller diameter =3D more damping). =
&nbsp;Best
not to think about it too hard, cuz it&#8217;s not that =
critical.</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Al</span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

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style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>&nbsp;</span></font></p>

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