X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 17 Feb 2010 14:38:55 -0500 Message-ID: X-Original-Return-Path: Received: from web57504.mail.re1.yahoo.com ([66.196.100.71] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with SMTP id 4128064 for lml@lancaironline.net; Wed, 17 Feb 2010 08:22:04 -0500 Received-SPF: none receiver=logan.com; client-ip=66.196.100.71; envelope-from=casey.gary@yahoo.com Received: (qmail 72807 invoked by uid 60001); 17 Feb 2010 13:21:28 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=u+kZ7HPJCGITXm4JUq/vg/8V0TKIOnsAhFYH8d52Xt7flNxNx72b28ntMdO12wW6zKrgO6rqUCvKA5M00X+aqngV93oKQiPDLO8vOW2l2RHPDM0Yo/gq9t6cdP0nR1m45YQtBJOVyenfvyPOCnpcy2qGnfzRAFNbFINcWTWuCYA=; X-Original-Message-ID: <500353.72557.qm@web57504.mail.re1.yahoo.com> X-YMail-OSG: gZBWEiwVM1kz6VoNWrIORBcJD5YoG699Bqt_tyDx4b71rOvU1_UY9aEdSnpdO4Fj2iExmXaH.BiRkaUv.U4qUYE5j3CWxkrb7C7r8F1wC.jTNi3XBeZojaS7Z0rH1WdaD_VuiCyhTn4VTvt6xRIQQ3YKmw_DC1ngx.i3XSEl8EZD9XJcJecj8yTAZwd7y2vs703cNlUSOSqNvFHqrEb4qY5MIAIBMj6141dIabRkg.KhSl91WECCrDAuGQow_WRyEaFgW6s8YFqafg0JbbgJSyFUIwEwSOugOn2mNznoGVcQ0qmbM1qJO3FJXJl7HhUAdhU01UfH9m7JPM4.wYSUOi4- Received: from [97.122.184.53] by web57504.mail.re1.yahoo.com via HTTP; Wed, 17 Feb 2010 05:21:28 PST X-Mailer: YahooMailRC/300.3 YahooMailWebService/0.8.100.260964 References: X-Original-Date: Wed, 17 Feb 2010 05:21:28 -0800 (PST) From: Gary Casey Subject: Re: Cowl pressure X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1009539842-1266412888=:72557" --0-1009539842-1266412888=:72557 Content-Type: text/plain; charset=us-ascii Chris, Thanks for posting the link to the most excellent report. But I have a couple of questions: You said you used a "pitot" probe in the inlet and reported the velocity at about 100% of aircraft velocity. But aren't you really measuring total pressure, which is the sum of the velocity and static pressures? So some of the pressure recovery could have been ahead of the inlet, which I think is a good place to have it. That reduces the amount of recovery that has to be done in the diffuser. I've seen two(at least) recommendations as to the shape of the diffuser section. Conventional wisdom seems to specify a constant angle to prevent separation at the downstream portion. Another recommendation was to use a bell-mouth exit as you have done. I couldn't follow the rationale for the bell-shaped exit so I used a nearly-constant angle with a sharp exit. Comment? Finally, I see that the pressure below the engine is very low and I would expect to see some losses as the low-velocity air exits the cowl. Wouldn't it be better to construct a small-area converging nozzle to provide for the exit? The lower cowl pressure would go up, but that would provide the energy to accelerate the air to something closer to the free-stream velocity. True? Thanks again for the excellent information. Gary ________________________________ Re: [LML] Cowl pressure February 16, 2010 7:15:25 AM MST From: "Chris Zavatson" To: "" Paul, That one doesn't have an easy singular answer. Figure 15 in the link below shows required mass flow and pressure drop and how this relates to CHT. Unfortunately it doesn't cover the most desirable CHT range. You can see what I measured on my plane in Figure 13. http://www.n91cz.com/Pressure/PlenumPressure.pdf Chris Zavatson N91CZ 360std www.N91CZ.com --0-1009539842-1266412888=:72557 Content-Type: text/html; charset=us-ascii
Chris,
Thanks for posting the link to the most excellent report.  But I have a couple of questions:  You said you used a "pitot" probe in the inlet and reported the velocity at about 100% of aircraft velocity.  But aren't you really measuring total pressure, which is the sum of the velocity and static pressures?  So some of the pressure recovery could have been ahead of the inlet, which I think is a good place to have it.  That reduces the amount of recovery that has to be done in the diffuser.  I've seen two(at least) recommendations as to the shape of the diffuser section.  Conventional wisdom seems to specify a constant angle to prevent separation at the downstream portion.  Another recommendation was to use a bell-mouth exit as you have done.  I couldn't follow the rationale for the bell-shaped exit so I used a nearly-constant angle with a sharp exit.  Comment?  Finally, I see that the pressure below the engine is very low and I would expect to see some losses as the low-velocity air exits the cowl.  Wouldn't it be better to construct a small-area converging nozzle to provide for the exit?  The lower cowl pressure would go up, but that would provide the energy to accelerate the air to something closer to the free-stream velocity.  True?
Thanks again for the excellent information.
Gary

Re: [LML] Cowl pressure

February 16, 2010 7:15:25 AM MST
From:
"Chris Zavatson" <chris_zavatson@yahoo.com>
To:
"" <lml@lancaironline.net>
Paul,
That one doesn't have an easy singular answer.
Figure 15 in the link below shows required mass flow and pressure drop and how this relates to CHT.  Unfortunately it doesn't cover the most desirable CHT range.
You can see what I measured on my plane in Figure 13.
 
Chris Zavatson
N91CZ
360std
 

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