REFLECTOR: Exhaust questions

[Chuck Harbert]

Brent, I think Sid is right about the cantilevered exhaust pipe causing a 
vibration (oscillation) due to the pulsing and vibration generated by the 
engine. Also, anytime you weld something, you get a weakening of the metal 
at the edge of the weld (known as the "heat affected zone"). I changed my 
straight out SS exhausts by cutting off the pipe just beyond the pipe coming 
down from the rear cylinder exhaust pipe,and then expanded it to slip over 
the remaining pipe. It no longer has as much leverage load to vibrate the 
pipe because they are not directly connected. To make sure the end pipe 
can't come off, I added a SS clamp with a dowel pin (1/8" SS socket bolt 
head)(this is normal a/c exhaust slip joint attachment procedure) that goes 
thru both pipes. Just to be safe, I also welded a gusset piece onto the end 
pipe so I could safety wire it to the forward part of the exhaust system. 
Not positive it will work, but 50 hrs, and no sign of distress.

Chuck H

p.s. Cutting off the end pipe was needed for the turbo system that will be 
installed next spring.

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Subject: Re: REFLECTOR: Exhaust Questions      Need durability and HP
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
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Several years ago I had a pipe break clean off.... only the safety wire kept
it from going thru the prop.  It made a lot of noise banging against the
cowling but I had only about 10 minutes flight to get back home so it could
have been worse (the wire would have broken after a while).  Actually, the
scary part was when the exhaust flame inside the cowling melted  the aileron
control cable and essentially froze-up aileron movement.  Luckily, I had a
straight-in, no wind so the plane was conrtrollable with rudders. Until I
landed and looked, I had no idea what was going-on... just that I wanted it
to never happen again.  It was a crappy design that had that "U" hanging out
there with no support.  It thought it was a tuning-fork and was only a
matter of time before it broke at the weld.  I modded both pipes as shown
and added a second safety cable held to the pipe with a SS hose-clamp.
Several hundred hours later and no more pipe breakage.

Not exactly what you were asking about but somewhat on-topic.

Sid Knox
Oklahoma

Velocity  173 RG  N199RS
Starduster  N666SK
KR2         N24TC
W7QJQ

----- Original Message ----- 
From: "brent bourgeois" <bjb3013 at yahoo.com>
To: <reflector at tvbf.org>
Sent: Wednesday, November 29, 2006 6:24 PM
Subject: REFLECTOR: Exhaust Questions Need durability and HP


>I have a few questions about the exhaust on my Lyc
> IO360 powered Std RG. I have the rear pointing
> stainless pipes from Velocity. The co pilot side (the
> long side) gets cracks every 60 to 100 hours right
> behind the #2 junction. No welds have cracked, always
> the pipe wall. This pipe has been trimmed as short as
> possible and still get past the fairing.I always have
> at least 2 pieces of thick safety wire on both sides
> to hold everything in in the event of total breakage.
> Is this normal?
>
> Why do the new pipes face forward? Why do I want all
> of this heat in the cowling. Do they have a long side
> and crack like the rear pointing pipes. Do they have
> slip joints? Why not weld up a set that drops straight
> down ?  Four pipes could be used or a 2 into 1
> pointing down. If the pipes point outward slightly
> they would not be over 12 inches long, possibly much
> shorter.
>
> I was told at the symposium that the standard Velocity
> pipes cost 2-6 horse power on a dyno. What size is
> optimum for the drop pipe and the tail pipe?
> Are any drawings available with dimensions to build
> your own. What type of stainless are the factory pipes
> and what thickness are they (would thicker help)
> Should I use 304 or 321 stainless.
>
> Thanks ahead of time for help with my project
> Brent
> 985-785-8299