Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2b6) with ESMTP id 300258 for flyrotary@lancaironline.net; Fri, 09 Jul 2004 06:15:23 -0400 Received: from EDWARD (clt25-78-058.carolina.rr.com [24.25.78.58]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i69AEKPg004453 for ; Fri, 9 Jul 2004 06:14:21 -0400 (EDT) Message-ID: <001501c4659d$81a19e20$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Turbo post mortem Date: Fri, 9 Jul 2004 06:14:22 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Virus-Scanned: Symantec AntiVirus Scan Engine John, I think you may be correct about the overspeed. That is one of the dangers with using a blow off valve as I mentioned before. The compressor wheel is already speeding huffing and puffing faster at altitude than sea level to produce the same amount of boost and suddenly you remove some of the resistance it is working against on the intake side through a blow off valve. Already revving at high speed because of the altitude with plenty of exhaust mass flow spinning the other end - the turbine the blow off valve suddenly reduces the pressure (and therefore resistance the compressor wheel sees) and with less load on the compressor wheel the rotating assembly rapidly increases in speed even more. A waste gate of course reduces the exhaust mass flow and slows the turbine down, a blow off valve (at least momentarily) simply reduces the boost by bleeding off the air the compressor is striving to pressurize to maintain the boost pressure. Yes, eventually the lack of boost will cause the exhaust flow to slow down - but not perhaps before overspeeding the rotating assembly. So while blow off valves may be OK for autos at sea level, I would really hesitate to put one on an aircraft. That of course just my personal opinion. Ed Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC ----- Original Message ----- From: "John Slade" To: "Rotary motors in aircraft" Sent: Thursday, July 08, 2004 10:43 PM Subject: [FlyRotary] Turbo post mortem > I took my (ex Rusty's) turbo apart this evening. The bearings seem to be in > fairly good shape and the shaft looks ok. It looks like the compressor wheel > just "came off the end" of the shaft, much like the other one did. My > uneducated guess would be that I overspeeded it. > > By the way, I was showing 38 MAP at 11,500 ft with the wastegate fully open. > However, there's an open 1/2 inch air bleed on the intercooler (to be > closed off) and a blow off valve, so the turbo may have been putting out > much more than the MAP showed. > > John Slade > Rotary Cozy IV > > > > > >> Homepage: http://www.flyrotary.com/ > >> Archive: http://lancaironline.net/lists/flyrotary/List.html >