REFLECTOR: Exhaust system design

Tue Apr 1 07:33:00 CDT 2008

Our aircraft have special considerations with exhaust.  In large part
because the prop is behind the engine.

No one wants to get the exhaust close enough to the prop to damage it.

As Keith wrote, the parts need to be supported.  Unfortunately, there have
been exhaust systems that failed in Velocities.  In one case, the aircraft
was lost.  The Pilot and Passenger survived unharmed.  When the pipe broke,
it is believed it exited the cowl and went through the prop.  I shattered
two blades.  The exhaust stump poured hot exhaust into the cowl.  They are
not sure what happened in the cowl after that as the plane burned.

-Andy

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Keith Hallsten
Sent: 04-01-2008 12:44
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Exhaust system design

I recall talking to the guys from PowerFlow at OSH when I was considering
how to specify my exhaust system.  They build tuned exhausts for certified
aircraft.  They didn't think they could get one in a Velocity cowl.

Exhaust design has a lot of contradictory requirements.  To minimize heat
damage to the cowl and engine hoses, cables and other parts you want to
minimize the amount of pipe that's in the cowl.  However, a tuned exhaust
requires quite a bit of pipe.  A separate consideration is fatigue - the
exhaust system needs to be relieved with slip joints at any points that
would otherwise support a vibrating cantilevered mass, and then be supported
separately.  That can be tough to engineer with a removable cowl.

In the end, I went with as short a system as I could conceive of, to
minimize both heat in the cowl and cantilevered mass.  Unfortunately, it's
going to be pretty loud!  There are two separate 3-into-1 headers with slip
joints on the center cylinder connections.  The exhaust is aimed downward,
with a 45-degree bend aft just as they come through the cowl.

Keith Hallsten
XLFG, IO-540

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of doug.holub at tx.rr.com
Sent: Monday, March 31, 2008 7:10 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: need some exhaust

Thanks. I'll give them a call tomorrow.

So I've been reading a bunch of stuff today about different exhaust systems.
Aparently a tuned exhaust system is able to improve engine performance by
sucking exhaust out of the cylinders and generally improve the airflow
through the engine. The difference between a tuned exhaust system and a bad
one is 10 or 15 hp.

Does anyone know if the stock forward facing Velocity exhaust pipes are very
good from a performance standpoint? How about the original out-the-back
pipes? 

Doug Holub
I see light at the end of the tunnel

---- Scott Derrick <scott at tnstaafl.net> wrote: 
> Doug
> 
> Call up Custom Aircraft Parts
> 1-800-561-1901
> 1-619-561-5757
> 
> http://www.customaircraft.com/
> 
> They can make any exhaust and you know you'll be getting the best..
> 
> I don't have any association to them other than I'm a very satisfied 
> customer for over 10 years
> 
> Scott
> 
> 
> doug.holub at tx.rr.com wrote:
> > For 3 weeks I've been trying to buy a forward facing exhaust system from
the factory for my IOX-360. They sold the last one they had the day before I
called them, and now they are having supplier trouble, and don't know when
they will get some more in stock. 
> > 
> > My engine is assembled at the shop, but he doesn't want to run it
without an exhaust system. Does anybody have any kind of 0-360 exhaust
system I could borrow for a week or so?
> > 
> > Alternatively, could I just go to an automotive exhaust shop, give them
the dimensions, and have them build me some?
> > 
> > Doug Holub
> > _______________________________________________
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