X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from vms046pub.verizon.net ([206.46.252.46] verified) by logan.com (CommuniGate Pro SMTP 5.1c.2) with ESMTP id 1317876 for flyrotary@lancaironline.net; Thu, 27 Jul 2006 00:28:23 -0400 Received: from verizon.net ([71.98.170.158]) by vms046.mailsrvcs.net (Sun Java System Messaging Server 6.2-4.02 (built Sep 9 2005)) with ESMTPA id <0J3100KPTOEG4KI9@vms046.mailsrvcs.net> for flyrotary@lancaironline.net; Wed, 26 Jul 2006 23:27:54 -0500 (CDT) Date: Thu, 27 Jul 2006 00:27:50 -0400 From: Finn Lassen Subject: Re: [FlyRotary] Re: Joe Hull's OSH Trip - Part 2 In-reply-to: To: Rotary motors in aircraft Message-id: <44C840C6.10105@verizon.net> MIME-version: 1.0 Content-type: multipart/alternative; boundary=------------040303020604090007060808 X-Accept-Language: en-us, en References: User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax; PROMO) This is a multi-part message in MIME format. --------------040303020604090007060808 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit At 1/8" I doubt you'll see the bends fail. How about the collector? Also 1/8" ? I guess that what we fail to envision is the amount the tubes "grow" when they are heated. Try to visualize an unequal increase of length of the different parts: bends, collector and then the resulting stresses from that. Then add vibration on top of that. I'm afraid that Bob White's muffler is bound to crack. The short runners are not going to move a lot but the collector is going to expand length-wise leading to cracks next to the welds in the collector. Very close to my failed design but perhaps thicker collector material than my 0.035 SS which didn't last 25 hours, and really just a few minutes after I started running above 5,500 RPM (could have been a resonance point that made things worse). I would agree with Bob that the number of factors involved makes it next to impossible to calculate. My muffler was supported so it definitely did not crack from "hanging on the welds". Finn Mark R Steitle wrote: > Finn, > > I think the flange does make some difference, just don't know how > much. The reason I think that is that the stock manifold has slotted > holes at two of the exhaust ports, allowing for the engine and/or the > manifold to move/grow without affecting the other or breaking the > studs. I did the same thing on my exhaust system. > > > > The bends came from R.G. Wagner and is 304-SS material, the same stuff > that Ed Anderson has used successfully for many hundreds of hours. > They are about 1/8" thick which absorbs much of the heat stresses, > similar to a cast iron manifold. Each bend passes through a close > tolerance chamfered hole and is welded on the back side nearest the > exhaust port. I didn't wrapped it so that I can inspect for cracks and > to allow the heat to escape. So far, no cracks. I do have a Zetex > aluminized fabric heat blanket on the upper and lower cowl in the > vicinity of the exhaust. It made a significant difference in cowl > temps. > > > > Mark S. > > > > ------------------------------------------------------------------------ > > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] > On Behalf Of Finn Lassen > Sent: Wednesday, July 26, 2006 10:09 AM > To: Rotary motors in aircraft > Subject: [FlyRotary] Re: Joe Hull's OSH Trip - Part 2 > > > > Sure looks good! Too good to change. > > I don't think that the flange has much significance. > > Time will tell, but you may find that the thermal stresses are where > the bends are welded to the collector. > > Now, you do have fairly long bends which may absorb the expansion. > Then again, the length of the bends may make it worse. > > A lot of factors here: difference of EGT of the three rotors, airflow > over the outside of the bends and collector, vibration, etc. > > In any case, please keep looking for cracks in the collector where the > bends are welded to it. > If so, you'll have to at lease cut two of the bends at a straight > point (near port?) and slide pieces of tubing over the cuts. Better > would be to add actual expansion joints. > > How thick is the material of the collector? > > If this were a pusher, definitely safety wire the collector! > > Finn > > Mark R Steitle wrote: > > Finn, > > > > Maybe that's why some of the aftermarket flanges are one piece. > That's how I made mine for that very reason. So far, so good. > > > > Mark S. > > > > ------------------------------------------------------------------------ > > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] > On Behalf Of Finn Lassen > Sent: Wednesday, July 26, 2006 9:37 AM > To: Rotary motors in aircraft > Subject: [FlyRotary] Re: Joe Hull's OSH Trip - Part 2 > > > > Ground running won't necessarily get you into that thermo cycle range. > Seems you consistently have to get above 5,000 RPM before anything > happens. > > No expansion joints: it will crack. > Unless you use ridiculously thick material. Which is probably why the > stock Mazda manifold is so heavy. > > Finn > > > --------------040303020604090007060808 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit At 1/8" I doubt you'll see the bends fail.
How about the collector? Also 1/8" ?

I guess that what we fail to envision is the amount the tubes "grow" when they are heated.
Try to visualize an unequal increase of length of the different parts: bends, collector and then the resulting stresses from that. Then add vibration on top of that.

I'm afraid that Bob White's muffler is bound to crack. The short runners are not going to move a lot but the collector is going to expand length-wise leading to cracks next to the welds in the collector. Very close to my failed design but perhaps thicker collector material than my  0.035 SS which didn't last 25 hours, and really just a few minutes after I started running above 5,500 RPM (could have been a resonance point that made things worse). I would agree with Bob that the number of factors involved makes it next to impossible to calculate.

My muffler was supported so it definitely did not crack from "hanging on the welds".

Finn

Mark R Steitle wrote:

Finn,

I think the flange does make some difference, just don’t know how much.  The reason I think that is that the stock manifold has slotted holes at two of the exhaust ports, allowing for the engine and/or the manifold to move/grow without affecting the other or breaking the studs.  I did the same thing on my exhaust system. 

 

The bends came from R.G. Wagner and is 304-SS material, the same stuff that Ed Anderson has used successfully for many hundreds of hours.  They are about 1/8” thick which absorbs much of the heat stresses, similar to a cast iron manifold.  Each bend passes through a close tolerance chamfered hole and is welded on the back side nearest the exhaust port. I didn’t wrapped it so that I can inspect for cracks and to allow the heat to escape.  So far, no cracks.  I do have a Zetex aluminized fabric heat blanket on the upper and lower cowl in the vicinity of the exhaust.  It made a significant difference in cowl temps.   

 

Mark S.

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Finn Lassen
Sent: Wednesday, July 26, 2006 10:09 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Joe Hull's OSH Trip - Part 2

 

Sure looks good! Too good to change.

I don't think that the flange has much significance.

Time will tell, but you may find that the thermal stresses are where the bends are welded to the collector.

Now, you do have fairly long bends which may absorb the expansion. Then again, the length of the bends may make it worse.

A lot of factors here: difference of EGT of the three rotors, airflow over the outside of the bends and collector, vibration, etc.

In any case, please keep looking for cracks in the collector where the bends are welded to it.
If so, you'll have to at lease cut two of the bends at a straight point (near port?) and slide pieces of tubing over the cuts. Better would be to add actual expansion joints.

How thick is the material of  the collector?

If this were a pusher, definitely safety wire the collector!

Finn

Mark R Steitle wrote:

Finn,

 

Maybe that’s why some of the aftermarket flanges are one piece.  That’s how I made mine for that very reason.  So far, so good.

 

Mark S.

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Finn Lassen
Sent: Wednesday, July 26, 2006 9:37 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Joe Hull's OSH Trip - Part 2

 

Ground running won't necessarily get you into that thermo cycle range. Seems you consistently have to get above 5,000 RPM before anything happens.

No expansion joints: it will crack.
Unless you use ridiculously thick material. Which is probably why the stock Mazda manifold is so heavy.

Finn

 
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