Return-Path: Received: from fed1rmmtao12.cox.net ([68.230.241.27] verified) by logan.com (CommuniGate Pro SMTP 4.2) with ESMTP id 374298 for flyrotary@lancaironline.net; Sun, 22 Aug 2004 14:05:07 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.27; envelope-from=ALVentures@cox.net Received: from BigAl ([68.107.116.221]) by fed1rmmtao12.cox.net (InterMail vM.6.01.03.02.01 201-2131-111-104-103-20040709) with ESMTP id <20040822180437.HJKI19929.fed1rmmtao12.cox.net@BigAl> for ; Sun, 22 Aug 2004 14:04:37 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: EM-2 MAP readings Date: Sun, 22 Aug 2004 11:04:50 -0700 Message-ID: <000001c48872$84c133c0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C48837.D8625BC0" 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 V6.00.2800.1165 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C48837.D8625BC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Subject: [FlyRotary] Re: EM-2 MAP readings =20 I'm thinking that the TB ports are affected by laminar/nonlaminar/turbulent flow in the TB bores influenced by throttle plate position/presence/etc. -Mike =20 Thanks for the comments Mike. I agree, and think it would be difficult = for the TB ports to read accurately at high velocity. That being said... =20 I just hung up with TWM, and they believe those ports are completely accurate in their TB. He asked what size TB I had, what engine, and = about what HP I thought it was capable of. After hearing all that, he said my = 42 mm bores were simply too small, and that I'd need at least 45's. When I pointed out that my runners were only about 42 mm, he basically said = "start over" :-) He did mention the possibility of adding a crossover tube between the two runners, to allow one to steal from the other, but I probably wouldn't do that unless I was committed to building another = intake if it didn't work. =20 =20 =20 Without hard evidence to the contrary; I think it is more likely that = the MAP readings we see on the TWM TB is valid, or close to it. The MAP = port is =BD=94 downstream, directly in line with the butterfly shaft, and = supposed to measure =91static=92 pressure in the manifold. Seems like a pretty good = spot to me. Of course there is all kinds of turbulence going on there, but my judgment says that it is a lot more likely that the pressure drop is in = the relatively long path upstream than some local condition that could exist over a cm or 2 in the TB barrel. I don=92t think there is any way to = sustain 3-4=94 HG pressure differential over a very short distance in the area = of the port. =20 Tracy and others are measuring MAP at the TB, BEFORE any losses in the intake runners. We are measuring near the intake port downstream from a single 1 =BE=94 runner per rotor (the TB barrel itself). So of course = we are not going to see ambient atmospheric pressure with WOT. OTOH; I also = find it hard to believe there could be that much pressure drop upstream. =20 =20 Atkins recommended to me not going larger than 44mm barrel dia./rotor = for better throttle response. That may not be important in our application. = In discussions with Paul Yaw; he seemed to agree that 44 mm was a good = choice based on getting the higher flow velocity. So who knows? What I know = is that I can=92t complain about the power my engine put out on the dyno. = 85 hp/rotor at 6000 rpm, and 96 hp/rotor at 7000 is not all that bad for = NA, 9.0 rotors and =93untuned=94 intake. And at 7000 rpm WOT I was reading = only about 24=94 MAP at that TWM port. =20 Since the power is there, what is the concern? Maybe something about = the EC2 response that expects a MAP reading taken at some other point? = Running WOT hp vs rpm curves on the dyno is a bit different than running on a = prop load curve. But I would think that setting up the mixture correction = table on the EC2 with the MAP port where it is should still give good results. =20 On the 3003 TB that I have, the MAP port connects to two of the three runners. I added an additional backup port in the third runner. The new port is similarly placed, but is 1=94 downstream from the butterfly = shaft instead of =BD=94. When I get running again, I=92ll check to see if the = readings are any different. =20 Al =20 =20 ------=_NextPart_000_0001_01C48837.D8625BC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message

Subject: [FlyRotary] Re: EM-2 MAP readings

 

I'm thinking that the TB ports are affected = by
laminar/nonlaminar/turbulent flow in the TB bores influenced by = throttle
plate position/presence/etc.

-Mike

 

Thanks for the = comments Mike.  I agree, and think it would be difficult for the TB ports to = read accurately at high velocity.  That being said...

 

I just hung up = with TWM, and they believe those ports are completely accurate in their TB.  = He asked what size TB I had, what engine, and about what HP I thought = it was capable of.  After hearing all that, he said my 42 mm bores = were simply too small, and that I'd need at least 45's.  When I = pointed out that my runners were only about 42 mm, he basically said "start over" :-)   He did mention the possibility of adding a = crossover tube between the two runners, to allow one to steal from the other, but = I probably wouldn't do that unless I was committed to building another = intake if it didn't work. 

 

 

Without hard = evidence to the contrary; I think it is more likely that the MAP readings we see = on the TWM TB is valid, or close to it.=A0 The MAP port is =BD” = downstream, directly in line with the butterfly shaft, and supposed to measure = ‘static’ pressure in the manifold.=A0 Seems like a pretty good spot to me.=A0 Of = course there is all kinds of turbulence going on there, but my judgment says = that it is a lot more likely that the pressure drop is in the relatively long = path upstream than some local condition that could exist over a cm or 2 in = the TB barrel.=A0 I don’t think there is any way to sustain 3-4” HG = pressure differential over a very short distance in the area of the = port.

 <= /font>

Tracy and = others are measuring MAP at the TB, BEFORE any losses in the intake runners.=A0 We = are measuring near the intake port downstream from a single 1 =BE” = runner per rotor (the TB barrel itself).=A0 So of course we are not going to see = ambient atmospheric pressure with WOT. =A0OTOH; I also find it hard to believe = there could be that much pressure drop upstream.=A0

 <= /font>

Atkins = recommended to me not going larger than 44mm barrel dia./rotor for better throttle = response. =A0That may not be important in our application.=A0 In discussions with Paul = Yaw; he seemed to agree that 44 mm was a good choice based on getting the higher = flow velocity. =A0So who knows?=A0 What I know is that I can’t complain = about the power my engine put out on the dyno.=A0 85 hp/rotor at 6000 rpm, and 96 = hp/rotor at 7000 is not all that bad for NA, 9.0 rotors and “untuned” = intake.=A0 And at 7000 rpm WOT I was reading only about 24” MAP at that TWM = port.

 <= /font>

Since the = power is there, what is the concern?=A0 Maybe something about the EC2 response = that expects a MAP reading taken at some other point? =A0Running WOT hp vs = rpm curves on the dyno is a bit different than running on a prop load curve.=A0 But = I would think that setting up the mixture correction table on the EC2 with the = MAP port where it is should still give good results.

 <= /font>

On the 3003 = TB that I have, the MAP port connects to two of the three runners.=A0 I added an = additional backup port in the third runner. The new port is similarly placed, but = is 1” downstream from the butterfly shaft instead of =BD”. =A0When I get = running again, I’ll check to see if the readings are any = different.

 <= /font>

Al

 

 

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