Return-Path: Received: from [24.25.9.103] (HELO ms-smtp-04-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2b7) with ESMTP id 310290 for flyrotary@lancaironline.net; Sat, 10 Jul 2004 10:27:17 -0400 Received: from EDWARD (clt25-78-058.carolina.rr.com [24.25.78.58]) by ms-smtp-04-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i6AEQiVw026909 for ; Sat, 10 Jul 2004 10:26:45 -0400 (EDT) Message-ID: <002701c46689$efa22470$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Three candidates for Turbo Failure Date: Sat, 10 Jul 2004 10:26:48 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0024_01C46668.6860E8F0" 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 This is a multi-part message in MIME format. ------=_NextPart_000_0024_01C46668.6860E8F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Good catch, Bill I think you are correct - duh! Only the turbine wheel is friction = welded on, the compressor wheel is held on by a nut. And of course, = you would see the turbine not the compressor wheel looking up the = exhaust. Sigh, all that analysis and discussion based on false premises = {:>). But, we still have the question as to why. My bet is still on = overspeeding of the rotating assembly OR I guess another possibility is = that John could have gotten two units with bad friction welds. Doesn't = seem likely but certainly possible. =20 Thanks for pointing that out, Bill Ed =20 Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC ----- Original Message -----=20 From: William=20 To: Rotary motors in aircraft=20 Sent: Saturday, July 10, 2004 9:23 AM Subject: [FlyRotary] Re: Three candidates for Turbo Failure 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_0024_01C46668.6860E8F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Good catch, Bill
 
    I think you are = correct -=20 duh!  Only the turbine wheel is friction welded on, the compressor = wheel=20 is  held on by a nut.  And of course, you would see the = turbine not=20 the compressor wheel looking up the exhaust. Sigh, all that analysis and = discussion based on false premises {:>).
 
   But, we still have the = question as to=20 why.  My bet is still on overspeeding of the rotating assembly OR I = guess=20 another possibility is that John could have gotten two units with bad = friction=20 welds.  Doesn't seem likely but certainly possible.
 
 
   Thanks for pointing that = out,=20 Bill
 
Ed
 
   
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From:=20 William=20
Sent: Saturday, July 10, 2004 = 9:23=20 AM
Subject: [FlyRotary] Re: Three = candidates=20 for Turbo Failure

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=20 wheel 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 Anderson
To: Rotary motors in = aircraft=20
Sent: Saturday, July 10, 2004 = 7:36=20 AM
Subject: [FlyRotary] Three = candidates=20 for 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=20 just not a random factor, but has some underlying common = cause.  I=20 agree if the compressor maps we are looking at are even close to the = Mazda=20 compressor parameters, it is unlikely that John was in the surge = zone. =20 If he had been according to what I have read, there would have been=20 indications like rapidly fluctuating pressure surges and sound and = vibration=20 associated.  Although with the engine at the back the sound may = not=20 have been heard and the vibration could have been dampened - which a = composite construct is good at.  So, apparently no evident to = support=20 the surge 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=20 zone.  The worst case situation for surge appears to be in = boost with=20 low mass flow, in other words operating toward the left on the mass = flow=20 axis of the chart. The further over you are the more like to enter = it. =20 But again - no 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=20 out, but I would put it further down the list.
 
My prime  candidate of = the three=20 would be overspeeding of the rotating assembly. 
 
 
The turbine wheel is generally = friction welded=20 to the shaft whereas the compressor wheel is held on with a = nut.  I=20 believe John indicated in one case the wheel was just laying in the=20 compressor housing and the in last case I believe he indicated it = was wedged=20 in tightly.  I don't recall how the nut is secured (other than=20 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=20 compressor wheel was.  I would assume that if it separated from = the=20 shaft 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=20 actually 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=20 back pressure across the compressor wheel when the BOV opens could = open the=20 possibility that the compressor could be stressed. If the back=20 pressure across the wheel suddenly drops and lessens the = load=20 while the turbine end is still getting the boost mass flow that = there is the=20 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=20 likely 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=20 more/less 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)=20 overheating, 2) turbo overspeading, or 3) compressors into the = surge=20 region.  While it is possible that there is a combined cause, = and=20 probable that more than one factor plays a partial role, most = likely ONE=20 factor is 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=20 are probably not in surge or overspeed region most of the = time. =20 Also, turbo overspeading and compressor surge are likely to = present with=20 very different symptoms like surging pressures or a disintegrated=20 turbo.  In contrast, overheating weakens the metals involved = and=20 would behave much like what John Describes.  In this case it = seems to=20 be turbine axle and possibly the blades that are not up to the=20 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=20 force acting on that axle, and possibly also slightly reduce the = heat=20 transfer.  My BOV (which I assume is fairly standard) is not = an=20 on/off valve, but a spring loaded valve that will open more or = less=20 depending on the pressure in the plenum, the ambient pressure, and = the=20 pressure differential across the throttle body.  There is no = way it=20 will instantly drop the pressure significantly.  In normal = operation=20 it would never go from full closed to full open suddenly, but = rather just=20 start leaking more and more air as the combination of those three=20 pressures changes.  The only time it would suddenly open is = when the=20 throttle is suddenly closed.
 
While on one hand it does seem very inefficient to = compress air=20 only to have it bleed out before entering the engine, I believe it = is far=20 more 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=20 will be transfeffed.  It is true that the faster RPM = increases the=20 radial stresses on the blades, but radial stresses are tolerated = much=20 better than the axial stresses caused by high back pressure.  = (Since=20 I have decided that heating is the problem and not=20 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=20 and waste gate I think the BOV is a helpful = addition.
 
Further, the BOV does provide some measure of protection = against=20 over boost like what happened to Todd.
 
Dave Leonard
 
------=_NextPart_000_0024_01C46668.6860E8F0--