Return-Path: Received: from [216.52.245.18] (HELO ispwestemail2.mdeinc.com) by logan.com (CommuniGate Pro SMTP 4.2b7) with ESMTP id 310249 for flyrotary@lancaironline.net; Sat, 10 Jul 2004 09:23:49 -0400 Received: from 7n7z201 (unverified [67.136.146.27]) by ispwestemail2.mdeinc.com (Vircom SMTPRS 3.1.302.0) with SMTP id for ; Sat, 10 Jul 2004 06:23:11 -0700 Message-ID: <002c01c46681$0b735a60$1b928843@7n7z201> From: "William" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Three candidates for Turbo Failure Date: Sat, 10 Jul 2004 08:23:05 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0029_01C46657.1FEC3C20" 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 This is a multi-part message in MIME format. ------=_NextPart_000_0029_01C46657.1FEC3C20 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Is it the compressor wheel or the turbine wheel that comes off. John = mentioned looking up the 'exhaust' pipe and seeing the compressor wheel = sitting at an angle, wedged in. I don't understand this -- seems that = looking up the exhaust you would see the turbine wheel, not the = compressor wheel. Also on the first failure, they talked about a 'bad = friction weld' as being the speculative cause.=20 My impression is that it was the hot turbine wheel that came off, and = john mentioned compressor wheel by error. Am I all wet???? Bill Schertz KIS Cruiser # 4045 ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Saturday, July 10, 2004 7:36 AM Subject: [FlyRotary] Three candidates for Turbo Failure I agree Dave. =20 This is of course all speculation about what actually happened to = John's turbo. But, at the moment, probably about the best we can do. = Having two failures that soon and with the same results - loose = compressor wheels - certainly indicates its probably just not a random = factor, but has some underlying common cause. I agree if the compressor = maps we are looking at are even close to the Mazda compressor = parameters, it is unlikely that John was in the surge zone. If he had = been according to what I have read, there would have been indications = like rapidly fluctuating pressure surges and sound and vibration = associated. Although with the engine at the back the sound may not have = been heard and the vibration could have been dampened - which a = composite construct is good at. So, apparently no evident to support = the surge hypothesis. It does appear that whatever is causing it, the stress appears to be = concentrated on the compressor wheel. Surges stress the entire rotating = assembly but does particularly stress the compressor wheel. I need to = sit down again and calculate the Pressure ratio and flow on the = compressor chart after adjusting for the pressure ratio creep caused by = altitude. But, it would seem to take a considerable increase in = pressure ratio to move him into the surge zone. The worst case = situation for surge appears to be in boost with low mass flow, in other = words operating toward the left on the mass flow axis of the chart. The = further over you are the more like to enter it. But again - no = indication that is happening. Overheating could indeed weaken the metal, however, its my opinion = that with the water cooling - overheating should not be a problem. I = mean almost all aircraft turbos I am aware of do not have water cooling = and survive for much longer, hundreds perhaps close to a thousand hours. = So you would think that with water cooling the Mazda turbo would do = even better - if overheating were the cause. Can't rule it out, but I = would put it further down the list. My prime candidate of the three would be overspeeding of the rotating = assembly.=20 The turbine wheel is generally friction welded to the shaft whereas = the compressor wheel is held on with a nut. I believe John indicated in = one case the wheel was just laying in the compressor housing and the in = last case I believe he indicated it was wedged in tightly. I don't = recall how the nut is secured (other than torque). I'll have to go down = to the shop later and take a look. =20 I don't recall John mentioning how damaged the compressor wheel was. = I would assume that if it separated from the shaft while spinning at = 80,000 + rpm it would really tear up the wheel and housing. On the = turbine side I have seen photos where the wheel actually tore through = the cast iron housing as hard as that might be to believe. =20 John do you have any photos of the wheels and housing after the = incidents?? I am still looking at the BOV and any possible role it may play. I = still appears to me that suddenly releasing the back pressure across the = compressor wheel when the BOV opens could open the possibility that the = compressor could be stressed. If the back pressure across the wheel = suddenly drops and lessens the load while the turbine end is still = getting the boost mass flow that there is the possibly of overspeeding = the rotating assembly.=20 I, of course, could be wrong and the BOV effects not only be benign = but actually helps prevent damage in an aircraft operating environment = as you and others have suggested. If aircraft turbo systems had blow = off valves then we would have another data point, but of the several = aircraft systems I looked on the internet had either sized the A/r of = the turbine housing or use a waste gate type of bleed for the exhaust.=20 Like you say it could be a combination of factors, but I do agree = with the three you mention as to being the most likely culprits. Ed Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC ----- Original Message -----=20 From: DaveLeonard=20 To: Rotary motors in aircraft=20 Sent: Saturday, July 10, 2004 12:42 AM Subject: [FlyRotary] Re: BOV more/less air flow Ed, Great write up! In general I very much agree with you on all = points but I want to free flow some thoughts that may modify people's = feeling about a BOV. I am even less of a turbo expert than you, but = here are some thoughts to consider. First, I think we have to figure out exactly what is causing John's = turbo's to fry. IMHO we have 3 general candidates 1) overheating, 2) = turbo overspeading, or 3) compressors into the surge region. While it = is possible that there is a combined cause, and probable that more than = one factor plays a partial role, most likely ONE factor is primarily = responsible for JTD (John's Turbos' Demise). IMHO that one factor is overheating. We know that heat is a factor = while according you the map you posted we are probably not in surge or = overspeed region most of the time. Also, turbo overspeading and = compressor surge are likely to present with very different symptoms like = surging pressures or a disintegrated turbo. In contrast, overheating = weakens the metals involved and would behave much like what John = Describes. In this case it seems to be turbine axle and possibly the = blades that are not up to the task. There are 2 ways to improve the situation. Reduce the heat, of = course, and reduce the forces acting on the metals. The BOV can be very = instrumental in reducing the force acting on that axle, and possibly = also slightly reduce the heat transfer. My BOV (which I assume is = fairly standard) is not an on/off valve, but a spring loaded valve that = will open more or less depending on the pressure in the plenum, the = ambient pressure, and the pressure differential across the throttle = body. There is no way it will instantly drop the pressure = significantly. In normal operation it would never go from full closed = to full open suddenly, but rather just start leaking more and more air = as the combination of those three pressures changes. The only time it = would suddenly open is when the throttle is suddenly closed. While on one hand it does seem very inefficient to compress air only = to have it bleed out before entering the engine, I believe it is far = more inefficient and potentially harmful to have the compressor = constantly fighting against a large pressure differential. That = pressure differential is the largest determinant of the force on the = axle. Further, if the turbine wheel is free to turn a little easier = (faster) it places less back pressure on the exhaust and less heat will = be transfeffed. It is true that the faster RPM increases the radial = stresses on the blades, but radial stresses are tolerated much better = than the axial stresses caused by high back pressure. (Since I have = decided that heating is the problem and not overspeeding.) There is no doubt that we both agree on the BEST solution: a larger = turbo with an even larger waste gate placed perhaps a little further = from the engine. But until I change my set-up to fit such a turbo and = waste gate I think the BOV is a helpful addition. Further, the BOV does provide some measure of protection against = over boost like what happened to Todd. Dave Leonard ------=_NextPart_000_0029_01C46657.1FEC3C20 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Is it the compressor wheel or the = turbine wheel=20 that comes off. John mentioned looking up the 'exhaust' pipe and seeing = the=20 compressor wheel sitting at an angle, wedged in. I don't understand this = --=20 seems that looking up the exhaust you would see the turbine wheel, not = the=20 compressor wheel.  Also on the first failure, they talked about a = 'bad=20 friction weld' as being the speculative cause.
 
My impression is that it was the hot = turbine wheel=20 that came off, and john mentioned compressor wheel by error. Am I all=20 wet????
 
Bill Schertz
KIS Cruiser # 4045
----- Original Message -----
From:=20 Ed=20 Anderson
Sent: Saturday, July 10, 2004 = 7:36=20 AM
Subject: [FlyRotary] Three = candidates for=20 Turbo Failure

I agree Dave. 
 
This is of course all speculation = about what=20 actually happened to John's turbo.  But, at the moment, probably = about=20 the best we can do.  Having two failures that soon and with the = same=20 results - loose compressor wheels - certainly indicates its = probably just=20 not a random factor, but has some underlying common cause.  I = agree if=20 the compressor maps we are looking at are even close to the Mazda = compressor=20 parameters, it is unlikely that John was in the surge zone.  If = he had=20 been according to what I have read, there would have been indications = like=20 rapidly fluctuating pressure surges and sound and vibration = associated. =20 Although with the engine at the back the sound may not have been heard = and the=20 vibration could have been dampened - which a composite construct is = good=20 at.  So, apparently no evident to support the surge=20 hypothesis.
 
It does appear that whatever is = causing it, the=20 stress appears to be concentrated on the compressor = wheel. =20 Surges stress the entire rotating assembly but does particularly = stress=20 the compressor wheel.  I need to sit down again and = calculate the=20 Pressure ratio and flow on the compressor chart after adjusting for = the=20 pressure ratio creep caused by altitude.  But, it would seem to = take a=20 considerable increase in pressure ratio to move him into the surge = zone. =20 The worst case situation for surge appears to be in boost with low = mass flow,=20 in other words operating toward the left on the mass flow axis of the = chart.=20 The further over you are the more like to enter it.  But again - = no=20 indication that is happening.
 
Overheating could indeed weaken the = metal,=20 however, its my opinion that with the water cooling - overheating = should not=20 be a problem.  I mean almost all aircraft turbos I am aware of do = not=20 have water cooling and survive for much longer, hundreds perhaps close = to a=20 thousand hours.  So you would think that with water cooling the = Mazda=20 turbo would do even better - if overheating were the cause. Can't rule = it out,=20 but I would put it further down the list.
 
My prime  candidate of the = three would=20 be overspeeding of the rotating assembly. 
 
 
The turbine wheel is generally = friction welded to=20 the shaft whereas the compressor wheel is held on with a nut.  I = believe=20 John indicated in one case the wheel was just laying in the compressor = housing=20 and the in last case I believe he indicated it was wedged in = tightly.  I=20 don't recall how the nut is secured (other than torque).  I'll = have to go=20 down to the shop later and take a look. 
I don't recall John mentioning how = damaged the=20 compressor wheel was.  I would assume that if it separated from = the shaft=20 while spinning at 80,000 + rpm it would really tear up the wheel and=20 housing.  On the turbine side I have seen photos where the wheel = actually=20 tore through the cast iron housing as hard as that might be to=20 believe.  
 
John do you have any photos of the = wheels and=20 housing after the incidents??
 
I am still looking at the BOV and any = possible=20 role it may play.  I still appears to me that suddenly releasing = the back=20 pressure across the compressor wheel when the BOV opens could open the = possibility that the compressor could be stressed. If the back=20 pressure across the wheel suddenly drops and lessens the = load while=20 the turbine end is still getting the boost mass flow that there is the = possibly of overspeeding the rotating assembly. 
 
 I, of course, could be wrong = and the=20 BOV effects not only be benign but actually helps prevent damage=20 in an aircraft operating environment as you and others have=20 suggested.     If aircraft turbo systems had blow off = valves=20 then we would have another data point, but of the = several aircraft=20 systems I looked on the internet had either sized the A/r of the = turbine=20 housing or use a waste gate type of bleed for the exhaust. =
 
 Like you say it could be a = combination of=20 factors, but I do agree with the three you mention as to being the = most likely=20 culprits.
 
Ed
 
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From:=20 DaveLeonard
To: Rotary motors in = aircraft=20
Sent: Saturday, July 10, 2004 = 12:42=20 AM
Subject: [FlyRotary] Re: BOV = more/less=20 air flow

Ed, Great write up!  In general I very much agree with = you on=20 all points but I want to free flow some thoughts that may modify = people's=20 feeling about a BOV.  I am even less of a turbo expert than = you, but=20 here are some thoughts to consider.
 
First, I think we have to figure out exactly what is = causing John's=20 turbo's to fry.  IMHO we have 3 general candidates 1) = overheating,=20 2) turbo overspeading, or 3) compressors into the surge = region.  While=20 it is possible that there is a combined cause, and probable that = more than=20 one factor plays a partial role, most likely ONE factor is=20 primarily responsible for JTD (John's Turbos'=20 Demise).
 
IMHO that one factor is overheating.  We know that = heat is a=20 factor while according you the map you posted we = are probably=20 not in surge or overspeed region most of the time.  Also, turbo = overspeading and compressor surge are likely to present with very = different=20 symptoms like surging pressures or a disintegrated turbo.  In = contrast,=20 overheating weakens the metals involved and would behave much like = what John=20 Describes.  In this case it seems to be turbine axle and = possibly the=20 blades that are not up to the task.
 
There are 2 ways to improve the situation. Reduce the heat, = of=20 course, and reduce the forces acting on the metals. =20 The BOV can be very instrumental in reducing the force = acting on that=20 axle, and possibly also slightly reduce the heat transfer.  My = BOV=20 (which I assume is fairly standard) is not an on/off valve, but a = spring=20 loaded valve that will open more or less depending on the pressure = in the=20 plenum, the ambient pressure, and the pressure differential across = the=20 throttle body.  There is no way it will instantly drop the = pressure=20 significantly.  In normal operation it would never go from full = closed=20 to full open suddenly, but rather just start leaking more and more = air as=20 the combination of those three pressures changes.  The only = time it=20 would suddenly open is when the throttle is suddenly=20 closed.
 
While on one hand it does seem very inefficient to compress = air only=20 to have it bleed out before entering the engine, I believe it is far = more=20 inefficient and potentially harmful to have the compressor = constantly=20 fighting against a large pressure differential.  That pressure=20 differential is the largest determinant of the force on the=20 axle.
 
Further, if the turbine wheel is free to turn a little = easier=20 (faster) it places less back pressure on the exhaust and less = heat will=20 be transfeffed.  It is true that the faster RPM increases the = radial=20 stresses on the blades, but radial stresses are tolerated much = better than=20 the axial stresses caused by high back pressure.  (Since I have = decided=20 that heating is the problem and not = overspeeding.)
 
There is no doubt that we both agree on the BEST solution: = a larger=20 turbo with an even larger waste gate placed perhaps a little further = from=20 the engine.  But until I change my set-up to fit such a = turbo and=20 waste gate I think the BOV is a helpful = addition.
 
Further, the BOV does provide some measure of protection = against over=20 boost like what happened to Todd.
 
Dave Leonard
 
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