X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from yw-out-2324.google.com ([74.125.46.29] verified) by logan.com (CommuniGate Pro SMTP 5.2.3) with ESMTP id 2959225 for flyrotary@lancaironline.net; Sun, 08 Jun 2008 23:35:09 -0400 Received-SPF: pass receiver=logan.com; client-ip=74.125.46.29; envelope-from=wdleonard@gmail.com Received: by yw-out-2324.google.com with SMTP id 3so1219071ywj.7 for ; Sun, 08 Jun 2008 20:34:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:in-reply-to:mime-version:content-type:references; bh=FuMFisuT90bFE1rerAb2+4S7prTm0jRSEwzgdXD8ZxU=; b=bxQcmNU8NbKycxw4WHK/RQ2X2lcPzB01nI0q0peSAyeBMiypD7sPqFXMEG+KrOC7xK K0TcHblJjFc0/cER8RKf90BLt+frzX9hfjeVGmmVdRYTHlx6q+SQs5vSROd+ur9WMN07 5bRlEjeddIkAimLqQqtEuo9RRIPF28WduyjY8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:in-reply-to:mime-version :content-type:references; b=bG8Tl5cymHMT6Mvr+DY/Jm8rPZp8BLPf0k+gO+kyvOsvjA153wUjL5qDC+Ox2tSlYl x7HTQp0RWb1/Me06EtmlAcOHpR0Ui2BSujbERgbcSHvrlNSpsrB2KWWuX8UY0Q+2RKDA RR5VawnSjATufacS9jy+IFwnORBkLc2HcOIhw= Received: by 10.150.156.20 with SMTP id d20mr5478864ybe.33.1212982470829; Sun, 08 Jun 2008 20:34:30 -0700 (PDT) Received: by 10.150.145.16 with HTTP; Sun, 8 Jun 2008 20:34:30 -0700 (PDT) Message-ID: <1c23473f0806082034j3d90d380j9b763e9f6c37db29@mail.gmail.com> Date: Sun, 8 Jun 2008 20:34:30 -0700 From: "David Leonard" To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] Exhaust and Muffler designs. In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_17199_10570541.1212982470830" References: ------=_Part_17199_10570541.1212982470830 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline As always Al, probably the best flying example I have seen! --=20 David Leonard Turbo Rotary RV-6 N4VY http://N4VY.RotaryRoster.net http://RotaryRoster.net On Sun, Jun 8, 2008 at 1:14 PM, Al Gietzen wrote: > Exhaust and muffler design in the rotary installation is one of the more > complex of all the installation issues. There are, and have been so many > variations among the various installations that there is little statistic= al > proof of anything. I'll add a few comments and opinions that may be > relevant, and describe what I did. It may trigger some ideas for you to > think about. My system on the 20B is now approaching 100 hours =96 not a = long > term proof =96 but it is still solid. > > > > The exhaust temps out of the port are very high, typically in the > neighborhood of 1600F, and sometimes maybe 1700F. Couple this with press= ure > pulses and vibrational loads, and corrosive environment, and you have a v= ery > demanding situation. When you look at material properties to handle this= , > things narrow down pretty rapidly, particularly if you also want light > weight as we do in aviation. Stainless steels, like 321, can handle the > temps and be a workable exhaust =96 but, design for low stress levels the= n > becomes a must, because SS are subject to 'stress corrosion' at these > temps. Combine the high temperatures and vibrational stress and you get > inter-granular corrosion which weakens the material and it eventually fal= ls > apart. > > > > On way to alleviate that is to use inconel. It gives you higher > temperature capability and corrosion resistance. And it gives you higher > cost. But is it worth it to reduce your risk a forced landing in an > unfriendly place? Compared to the total cost of your airplane it's a sma= ll > amount. Maybe cut cost somewhere where it is less critical to safety. > > > > Another thing to consider is that the more quickly you can expand the > exhaust gas, the more quickly you can deal with lower temperatures. Char= les > Law =96 temp (degree K) goes down in direct proportion to increased volum= e. > This becomes more complex in an exhaust system because of other factors, = but > it still works in your favor. The gas will expand down a constant diamet= er > pipe, but expanding into a BIG pipe can make a significant drop. > > > > That can be one of the advantages of the tangential muffler/manifold, or > the design that Neil presented. The amount of the temp drop of course > depends on the pressure in that bigger can. These designs have their own > possible failure modes associated with welded joints and thermal stresses= , > but at least there is nothing there that is going to plug up the flow > downstream. The skill of the welder and the post-weld heat treatment are > important factors. > > > > These units are generally bolted directly to the engine via the short > header pipes, so vibration loads are a factor. Ideally you'd like to have > stress (and thermal expansion) de-coupling between the engine and the > muffler/manifold, but since the engine can move relative to it's mount yo= u > either have to accommodate significant movement, or support it to the eng= ine > by some other means then the header pipes. > > > > And then there is the matter of the exit pipe(s) and secondary mufflers. > Those have to be supported as well =96 an unsupported length of pipe exte= nding > from the muffler is an ideal candidate for some vibrational resonance whi= ch > will fail the system somewhere. And the further away from the engine > centerline, the greater the loads. > > > > My exhaust system is shown in the first attached photo. This is in a push= er > configuration. It is an inconel tangential manifold/muffler supported to > the engine by short inconel header pipes which are welded to a heavy RB > steel flange. It has a convex 'head' at the front, and a conical outlet t= o > the exit pipe. It has internal vanes welded at an angle on the inside > surface opposite the exit from the headers (you can see the welds on the > outside) to help break up the pulses and direct the exhaust toward the ex= it. > They also prevent possible "swirl-flow choking" which could increase back > pressure. There are 'straightening' vanes in the conical exit section. > > > > The exit pipe is clamped (custom heavy SS clamp) to the inlet pipe of the > secondary muffler (I'll call it a resonator). The resonator is also of m= y > design and is made of 321 SS. It is basically a straight through 2 =BE" = pipe > that is drilled full of =BC" holes (about 100), contained within outer 5"= dia. > pipe. The inner pipe has an orifice plate at the center which has a 1 5/= 8" > opening. This orifice produces some restriction to the flow through the > resonator to force some of it outward through the holes, and back through > the holes to exit. The purpose of the resonator is to knock down the > pressure peaks a bit more. Measurements on the dyno showed that resonato= r > knocked another 8 db off the sound level and had no noticeable effect on = the > HP. > > > > The plug in the resonator closes a port originally intended for the O2 > sensor. But it didn't work well in that location because the temperature = was > too low (interesting, huh). I had to move it to the inlet pipe. > > > > Last but not least, there is a SS support at the end which clamps solidly > to the redrive. The clamp is designed to be rigid laterally, but to also = be > an effective heat choke. This supports the resonator, and reduces the > likelihood of any resonance vibration in the system. > > > > I originally thought that the resonator internals may not last more than = 50 > hours, but at 95 hours they are still solid. Which brings up another poin= t. > It is easily inspected. I can see those internals from the exit end, and = I > can stick a screwdriver or ratchet handle or whatever; in there and bang > around to be sure things are sound. I inspect all the welds in the exhau= st > system every time I remove the cowl, or at least every 10 hours or so. M= ake > your system inspectable, and keep an eye on it. > > > > I wouldn't call it "quiet", but I've had people say they like the way it > sounds. Time will tell its reliability. > > > > Best, > > > > Al Gietzen > > > > > > If you go through the archives, you'll find lots of examples = of > > failed muffler designs. Many by your's truly. I think I've tried every > > concoction known to man and the Swiss. They all worked... for a while. > > My best overall design (see attached) is a 2" tube, full of > holes > > inside a 5" tube. All made of 16ga SS, all welded together. Needless to > > say, the flange is more like 3/16" - 1/4" SS. The inside end of the 2" > tube > > is welded to the end cap of the 5" tube. That blocks off the one end of > the > > 2" tube and secures it from movement. The exhaust end of the 2" tube is > > welded through a 2" hole in the other 5" end cap. Rather than drilling t= he > > 2" tube full of round holes, we cut slots with a saw. Then take a big fl= at > > blade screwdriver, stick it in the slot and bend it over. This creates a= n > > oblong hole. (Much easier than drilling into SS. This is what will go o= n > > the Volmer. > > > > The sound is quite acceptable, it fits inside the cowl and Ji= m > M.'s > > version lasted the life of the aircraft... 600+ hours. > > > > Neil > > > > PS: Are you considering Rough River? > > > > > > > > -----Original Message----- > > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On > > Behalf Of Al Wick > > Sent: Saturday, June 07, 2008 4:57 PM > > To: Rotary motors in aircraft > > Subject: [FlyRotary] Re: Mistral Crash Analysis > > > > C'mon guys. You do this every time there's a crash. Instantly go into > > rationalization mode. It's unhealthy. Greatly increases risk builders won= 't > > > take action. Increases risk you won't research it thoroughly. > > > > A healthy response would be:" Here's another example of how our engines > > produce unusually destructive exhaust temperature and pulses. We have a > rich > > > > history of broken exhaust components. We need to be very thorough when > > designing and building exhaust." > > > > I designed my own muffler. It had two inlets, two outlets. So if (when) m= y > > muffler failed, it could never block both pipes. I also put loose safety > > wire around my pipes, because on a pusher loosing pipe wipes out prop. So > > basically, I assume stuff will fail, then design it to control the way i= t > > fails. I've heard of rotary guys doing same type of thing. This is a good > > time to share those key items. > > > > On your car, they deliberately design products to fail a certain way. The= y > > will make a component weak, so it fails first. They do that with wheels a= nd > > > hubs. So when the muffler fails, little pieces come apart, not big > sections? > > > > You guys do a great job of sharing successes, design and construction > > details. This is another opportunity. > > > > -al wick > > > > > > > > > > > to bad mouth the rotary - this will only be more ammunition. "See! even > > with umpteen million dollars you can't get one to fly" {:>). But, I > > serious doubt it will effect many who have researched the rotary and come > to > > > > understand its benefits - as for the rest, who cares {:>) > > > > > > > I'm certain it was a relief to Mistral that the culprit was not one of > > their engine components. > > > > > > > > Whew! a close one for sure. > > > > > > > > Hi Ed, > > > > > > > > Unfortunately, I bet the majority of people will only hear "Mistral > > rotary", "lost power", and "crash" :-( > > > > > > > > Rusty (RV-3 taking forever.) > > > > ____________________________________________________________ > > Orlando Vacations - Click Here! > > > http://thirdpartyoffers.juno.com/TGL2141/fc/Ioyw6i3nK7u59LkagfZ5IcEgGqYcv= PRC > > wA85GgQITbFK9vE7wPGKFP/ > > > > -- > > Homepage: http://www.flyrotary.com/ > > Archive and UnSub: > > http://mail.lancaironline.net:81/lists/flyrotary/List.html > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html > > ------=_Part_17199_10570541.1212982470830 Content-Type: text/html; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline
As always Al, probably the best flying example I have seen!
 
--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net

On Sun, Jun 8, 2008 at 1:14 PM, Al Gietzen <<= a href=3D"mailto:ALVentures@cox.net">ALVentures@cox.net> wrote:

Exhaust and muffler design in the rotary installation is on= e of the more complex of all the installation issues. There are, and have b= een so many variations among the various installations that there is little= statistical proof of anything.  I'll add a few comments and opinions = that may be relevant, and describe what I did. It may trigger some ideas fo= r you to think about. My system on the 20B is now approaching 100 hours =96= not a long term proof =96 but it is still solid.

 

The exhaust temps out of the port are very high, typically = in the neighborhood of 1600F, and sometimes maybe 1700F.  Couple this = with pressure pulses and vibrational loads, and corrosive environment, and = you have a very demanding situation.  When you look at material proper= ties to handle this, things narrow down pretty rapidly, particularly if you= also want light weight as we do in aviation.  Stainless steels, like = 321, can handle the temps and be a workable exhaust =96 but, design for low= stress levels then becomes a must, because SS are subject to 'stress corro= sion' at these temps.  Combine the high temperatures and vibrational s= tress and you get inter-granular corrosion which weakens the material and i= t eventually falls apart.

 

On way to alleviate that is to use inconel.  It gives = you higher temperature capability and corrosion resistance.  And it gi= ves you higher cost.  But is it worth it to reduce your risk a forced = landing in an unfriendly place?  Compared to the total cost of your ai= rplane it's a small amount.  Maybe cut cost somewhere where it is less= critical to safety.

 

Another thing to consider is that the more quickly you can = expand the exhaust gas, the more quickly you can deal with lower temperatur= es.  Charles Law =96 temp (degree K) goes down in direct proportion to= increased volume.  This becomes more complex in an exhaust system bec= ause of other factors, but it still works in your favor.  The gas will= expand down a constant diameter pipe, but expanding into a BIG pipe can ma= ke a significant drop.  

 

That can be one of the advantages of the tangential muffler= /manifold, or the design that Neil presented.  The amount of the temp = drop of course depends on the pressure in that bigger can. These designs ha= ve their own possible failure modes associated with welded joints and therm= al stresses, but at least there is nothing there that is going to plug up t= he flow downstream.  The skill of the welder and the post-weld heat tr= eatment are important factors.

 

These units are generally bolted directly to the engine via= the short header pipes, so vibration loads are a factor. Ideally you'd lik= e to have stress (and thermal expansion) de-coupling between the engine and= the muffler/manifold, but since the engine can move relative to it's mount= you either have to accommodate significant movement, or support it to the = engine by some other means then the header pipes.

 

And then there is the matter of the exit pipe(s) and second= ary mufflers. Those have to be supported as well =96 an unsupported length = of pipe extending from the muffler is an ideal candidate for some vibration= al resonance which will fail the system somewhere. And the further away fro= m the engine centerline, the greater the loads.

 

My exhaust system is shown in the first attached photo. Thi= s is in a pusher configuration.  It is an inconel tangential manifold/= muffler supported to the engine by short inconel header pipes which are wel= ded to a heavy RB steel flange. It has a convex 'head' at the front, and a = conical outlet to the exit pipe.  It has internal vanes welded at an a= ngle on the inside surface opposite the exit from the headers (you can see = the welds on the outside) to help break up the pulses and direct the exhaus= t toward the exit. They also prevent possible "swirl-flow choking" which co= uld increase back pressure.  There are 'straightening' vanes in the co= nical exit section.

 

The exit pipe is clamped (custom heavy SS clamp) to the inl= et pipe of the secondary muffler (I'll call it a resonator).  The reso= nator is also of my design and is made of 321 SS.  It is basically a s= traight through 2 =BE" pipe that is drilled full of =BC" holes (about 100),= contained within outer 5" dia. pipe.  The inner pipe has an orifice p= late at the center which has a 1 5/8" opening.  This orifice produces = some restriction to the flow through the resonator to force some of it outw= ard through the holes, and back through the holes to exit.  The purpos= e of the resonator is to knock down the pressure peaks a bit more.  Me= asurements on the dyno showed that resonator knocked another 8 db off the s= ound level and had no noticeable effect on the HP.

 

The plug in the resonator closes a port originally intended= for the O2 sensor. But it didn't work well in that location because the te= mperature was too low (interesting, huh). I had to move it to the inlet pip= e.

 

Last but not least, there is a SS support at the end which = clamps solidly to the redrive. The clamp is designed to be rigid laterally,= but to also be an effective heat choke.  This supports the resonator,= and reduces the likelihood of any resonance vibration in the system.

 

I originally thought that the resonator internals may not l= ast more than 50 hours, but at 95 hours they are still solid. Which brings = up another point.  It is easily inspected. I can see those internals f= rom the exit end, and I can stick a screwdriver or ratchet handle or whatev= er; in there and bang around to be sure things are sound.  I inspect a= ll the welds in the exhaust system every time I remove the cowl, or at leas= t every 10 hours or so.  Make your system inspectable, and keep an eye= on it.

 

I wouldn't call it "quiet", but I've had people say they li= ke the way it sounds. Time will tell its reliability.

 

Best,

 

Al Gietzen

 

 <= /span>

 &= nbsp;          If you go throu= gh the archives, you'll find lots of examples of

failed = muffler designs.  Many by your's truly.  I think I've tri= ed every

concoct= ion known to man and the Swiss.  They all worked...  for a while.=  

 &= nbsp;          My best overall= design (see attached) is a 2" tube, full of holes

inside = a 5" tube.  All made of 16ga SS, all welded together.  Needl= ess to

say, th= e flange is more like 3/16" - 1/4" SS.  The inside end of th= e 2" tube

is weld= ed to the end cap of the 5" tube.  That blocks off the one end of= the

2"= tube and secures it from movement.  The exhaust end of the 2" tu= be is

welded = through a 2" hole in the other 5" end cap.  Rather than dril= ling the

2"= tube full of round holes, we cut slots with a saw.  Then take a big f= lat

blade s= crewdriver, stick it in the slot and bend it over.  This creates an

oblong = hole.  (Much easier than drilling into SS.  This is what will go = on

the Vol= mer.

 <= /span>

 &= nbsp;          The sound is qu= ite acceptable, it fits inside the cowl and Jim M.'s

version= lasted the life of the aircraft... 600+ hours.

 <= /span>

Neil

 <= /span>

PS: Are= you considering Rough River?

 <= /span>

 <= /span>

 <= /span>

-----Or= iginal Message-----

From: R= otary motors in aircraft [mailto:flyrotary@lancaironline.net] On

Behalf = Of Al Wick

Sent: <= /span>Saturday, June 07, 2008 4:57 PM

To: Rot= ary motors in aircraft

Subject= : [FlyRotary] Re: Mistral Crash Analysis

 <= /span>

C'm= on guys. You do this every time there's a crash. Instantly go into

rationa= lization mode. It's unhealthy. Greatly increases risk builders won'= t

take ac= tion. Increases risk you won't research it thoroughly.

 <= /span>

A healt= hy response would be:" Here's another example of how our engines <= /span>

produce= unusually destructive exhaust temperature and pulses. We have a rich

 <= /span>

history= of broken exhaust components. We need to be very thorough when

designi= ng and building exhaust."

 <= /span>

I desig= ned my own muffler. It had two inlets, two outlets. So if (when) my =

muffler= failed, it could never block both pipes. I also put loose safety

wire ar= ound my pipes, because on a pusher loosing pipe wipes out prop. So <= /font>

basical= ly, I assume stuff will  fail, then design it to control the way it

fails. = I've heard of rotary guys doing same type of thing. This is a good

time to= share those key items.

 <= /span>

On your= car, they deliberately design products to fail a certain way. They =

will ma= ke a component weak, so it fails first. They do that with wheels and

hubs. S= o when the muffler fails, little pieces come apart, not big sections?

 <= /span>

You guy= s do a great job of sharing successes, design and construction

details= . This is another opportunity.

 <= /span>

-al wic= k

 <= /span>

 <= /span>

 <= /span>

 <= /span>

<No = doubt you are on the money, Rusty.  When folks are already predisposed=

to bad = mouth the rotary - this will only be more ammunition.  "See! even=

with um= pteen million dollars you can't get one to fly"  {:>).&nbs= p; But, I

serious= doubt it will effect many who have researched the rotary and come to

 <= /span>

underst= and its benefits - as for the rest, who cares {:>)

>

 <= /span>

  = I'm certain it was a relief to Mistral that the culprit was not one of =

their e= ngine components.

 <= /span>

 <= /span>

 <= /span>

  = Whew! a close one for sure.

 <= /span>

 <= /span>

 <= /span>

  = Hi Ed,

 <= /span>

 <= /span>

 <= /span>

  = Unfortunately, I bet the majority of people will only hear "Mistral

rotary&= quot;, "lost power", and "crash"  :-(

 <= /span>

 <= /span>

 <= /span>

  = Rusty (RV-3 taking forever.)

 <= /span>

_______= _____________________________________________________

Orlando= Vacations - Click Here!

http://thirdpartyoffers.juno.com/TGL2141/fc/Ioyw6i= 3nK7u59LkagfZ5IcEgGqYcvPRC

wA85GgQ= ITbFK9vE7wPGKFP/

 <= /span>

--

Homepag= e:  http://www= .flyrotary.com/

Archive= and UnSub:

http://mail.lancaironline.net:81/lists/flyrotary/List.html


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