Return-Path: Received: from fed1rmmtao09.cox.net ([68.230.241.30] verified) by logan.com (CommuniGate Pro SMTP 4.2.4) with ESMTP id 450389 for flyrotary@lancaironline.net; Sat, 02 Oct 2004 12:39:20 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.30; envelope-from=ALVentures@cox.net Received: from BigAl ([68.107.116.221]) by fed1rmmtao09.cox.net (InterMail vM.6.01.03.04 201-2131-111-106-20040729) with ESMTP id <20041002163850.VXCZ11855.fed1rmmtao09.cox.net@BigAl> for ; Sat, 2 Oct 2004 12:38:50 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: MAP pulses (20B) Date: Sat, 2 Oct 2004 09:38:59 -0700 Message-ID: <000001c4a89e$51724940$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C4A863.A5137140" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C4A863.A5137140 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable 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 ------=_NextPart_000_0001_01C4A863.A5137140 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

Al

 

 

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