Return-Path: Received: from [65.23.108.33] (HELO mail.tsisp.com) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP-TLS id 2751953 for flyrotary@lancaironline.net; Wed, 19 Nov 2003 16:11:39 -0500 Received: from stevehome ([]) by mail.tsisp.com (Technical Support Inc.) with ASMTP id BGA74184 for ; Wed, 19 Nov 2003 16:11:39 -0500 From: "Steve Brooks" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: gauges Date: Wed, 19 Nov 2003 16:13:28 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook, Build 11.0.4920 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Thread-Index: AcOup+pKkagC2EuATburf3ckLY0XdgAOXx9A In-Reply-To: Message-ID: I've been reading these emails between you and Rusty and John with great interest. I am really confused now. I have a boost gauge made by VDO. It reads both suction 0-30hg and = boost 0-+25hg. The center scale (0) is at the 1 o'clock position or there = about. I thought that this is what I need to monitor the turbo boost level, but now, I don't have a clue. I'm not sure what this gauge is going to show me. Steve Brooks=20 Cozy MKIV #1071 13BT=20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Marvin Kaye Sent: Wednesday, November 19, 2003 9:18 AM To: Rotary motors in aircraft e.g. roughly speaking boost PSI =3D (MAP - height thousands)-30/2 MAP =3D 42 @ SL =3D 6PSI MAP =3D 48 @ 10,000 =3D 4PSI Does this makes sense, or am I still missing something?

Your formula only works at sea level when ambient pressure is at 30"hg. = At altitude ambient pressure decreases about 1"/1kft. (That number isn't linear, the decrease diminishes with each thousand feet, but it's ok to = use that number for our purposes here...) So, if your MAP at 10kft was 48" where ambient pressure is about 20"hg you'd have 28" or 14psi of boost, = not 4.=20 Ergo, your formula should actually be: boost PSI =3D (MAP - ambient press)/2.=20 Both MAP and ambient pressure are in inches of mercury. If you run = some other numbers you can quickly see how a manifold vacuum gauge works... = let's say you're at 2000' msl where the ambient pressure is about 28"hg and = you pull the power to initiate a descent... your MAP gauge might read = 15"hg...=20 (15-28)/2 says you have 6.5psi of suction going on inside the manifold = and you're not making any boost at all. I don't know if they even make a = boost gauge that shows manifold vacuum (suction) as well as boost (positive pressure), but if they do the zero psi point would have to be referenced = to ambient pressure in order for it to display properly. BTW, in reality, = 1psi =3D 14.695" hg, but that's close enough to 2psi =3D 30"hg for purposes = of our discussion. >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.541 / Virus Database: 335 - Release Date: 11/14/2003 =20