X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 08 Aug 2005 23:00:57 -0400 Message-ID: X-Original-Return-Path: Received: from imo-m27.mx.aol.com ([64.12.137.8] verified) by logan.com (CommuniGate Pro SMTP 4.3.7) with ESMTP id 641902 for lml@lancaironline.net; Mon, 08 Aug 2005 17:31:20 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.8; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m27.mx.aol.com (mail_out_v38_r4.1.) id q.1e3.4186e401 (4320) for ; Mon, 8 Aug 2005 17:30:33 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: <1e3.4186e401.302928f8@aol.com> X-Original-Date: Mon, 8 Aug 2005 17:30:32 EDT Subject: Re: [LML] Ram Air Flowback X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1123536632" X-Mailer: 9.0 Security Edition for Windows sub 5009 X-Spam-Flag: NO -------------------------------1123536632 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 8/8/2005 3:53:44 P.M. Central Standard Time, wfhannahan@yahoo.com writes: To accurately test the effectiveness of a ram air system put a selector valve on the pitot port of your airspeed indicator allowing you to switch between pitot pressure and manifold pressure. Compare the two indicated speeds. If there is no change you have a great ram air system. Bill, Not so. However, one might construct a pitot tube and switch it into your MAP sensor. 1. Engine ram pressure includes air that is being drawn off occasionally depending on valve and piston position. A closed pitot air speed system is closed. 2. MAP is an absolute measure - not relative to ambient as measured thru a static air port. 3. The theoretical max ram air pressure from attained air speed can be calculated - i.e. KIAS "Hg (approximate) 248 3" (Legacy) 200 2" (Lancair 360) 175 1.5" (Lancair 320) 150 1" (Cozy 360) 125 .75" (Liberty) Thus, if your airplane is slow (<125 KIAS), you will see less benefit from ram air and even less if you ignore .4" Hg because of where the air comes from. Of course, you must be operating WOT to reap the benefit of the wings flying at the less draggy altitude whilst your engine believes it is several thousand feet lower.. Scott Krueger AKA Grayhawk Lancair N92EX IO320 SB 89/96 Aurora, IL (KARR) -------------------------------1123536632 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

In a message dated 8/8/2005 3:53:44 P.M. Central Standard Time,=20 wfhannahan@yahoo.com writes:

<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>To=20 accurately test the effectiveness of a ram air system put a selector
va= lve=20 on the pitot port of your airspeed indicator allowing you to switch
bet= ween=20 pitot pressure and manifold pressure. Compare the two indicated
speeds.= If=20 there is no change you have a great ram air system.=20

Bill,

Not so. However, one might construct a pitot tube and switch it i= nto=20 your MAP sensor.

1. Engine ram pressure includes air that is being drawn off occasionall= y=20 depending on valve and piston position. A closed pitot air speed syste= m is=20 closed.

2. MAP is an absolute measure - not relative to ambient as measured thr= u a=20 static air port.

3. The theoretical max ram air pressure from attained air speed ca= n be=20 calculated - i.e.

KIAS "Hg (approximate)

248 3" (Legacy)

200 2" (Lancair=20 360)

175 1.5" (Lancair 320)

150 1" (Cozy=20 360)

125 .75" (Liberty)

Thus, if your airplane is slow (<125 KIAS), you will see less benefi= t=20 from ram air and even less if you ignore .4" Hg because of where the air com= es=20 from.

Of course, you must be operating WOT to reap the benefit of the wi= ngs=20 flying at the less draggy altitude whilst your engine believes it is several= =20 thousand feet lower..=20

Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL=20 (KARR)

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