Return-Path: Received: from asmtp-a063f33.pas.sa.earthlink.net ([207.217.120.149] verified) by logan.com (CommuniGate Pro SMTP 4.2b6) with ESMTP id 300419 for flyrotary@lancaironline.net; Fri, 09 Jul 2004 09:54:08 -0400 Received: from adsl-69-212-48-22.dsl.sfldmi.ameritech.net ([69.212.48.22] helo=[192.168.1.101]) by asmtp-a063f33.pas.sa.earthlink.net with asmtp (TLSv1:AES256-SHA:256) (Exim 4.34) id 1Bivon-0001mr-7e for flyrotary@lancaironline.net; Fri, 09 Jul 2004 06:53:37 -0700 Message-ID: <40EEA325.5050406@chartermi.net> Date: Fri, 09 Jul 2004 09:52:37 -0400 From: "ericruttan@chartermi.net" Reply-To: ericruttan@chartermi.net User-Agent: Mozilla Thunderbird 0.6 (Windows/20040502) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: Turbo post mortem References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-ELNK-Trace: f9e70479b5cf6c9fd780f4a490ca69564776905774d2ac4ba3e997f6d0d39c09eb10dc0e0d1ec87f350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 69.212.48.22 Ed; Wouldn't an opening in the intake like john had shift the air mass the compressor is putting out to the right in the compressor map? I though John put the hole there to AVOID over speeding, (John has since explained that was not his INTENT). The idea being, relative to a compressor map, instead of going up the map, increasing the pressure ratio, it moves right, increasing air mas, but keeping in a safe pressure ratio. Less efficient, but no surge. Ed Anderson wrote: > 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 >> > > > >>> Homepage: http://www.flyrotary.com/ >>> Archive: http://lancaironline.net/lists/flyrotary/List.html > >