REFLECTOR: Repairs

Fri Sep 21 13:47:19 CDT 2012

Not all Velo use the factory exhaut solution.  This is 44VF, Brett and
Elizabeth's XLFG.  It has a custom exhaust feeds in to a rear facing about
4 inch tube.  Although we have never been able to perform any testing that
demonstrated that the exhaust pumps cooling air, I do know that the engine
stay cool even on extend time on the ground.  I believe this approach was
common in the earlier aircraft.  It certainly is widely used on EZ's.  I
believe the orignial research on the details of how this works and the
details of how best to design this augmentor was done for the old coal
fired locomotives.  As I recall the best approach is to have some small
distance between the start of the augmentor and the end of the exhaust.
This provides to advantages.  It pumps air through and it provides
extraction on the exhaust.

[LINK: http://www.velocityxl.com/album.php?albumid=4&attachmentid=2566]

Jerry Brainard
Jerry at JLBEnt.com

  	-------Original Message-------
From: Mark Magee
To: Velocity Aircraft Owners and Builders list
Cc: reflector at tvbf.org
Subject: Re: REFLECTOR: Repairs
Sent: Sep 21 '12 1:13pm

The exhaust exit inside the cowl facing the cooling air exit serves the
function of 'scavenging' the cooling air upon the Venturi principle. More
and more EZ's are going that way. If Velo exhaust exited at our rear
cooling air exits it would be a no brainer to implement this setup. Bottom
cowl exit is more challenging due to thermodynamics (rising heat).
I am still considering how I can implement bottom cowl scavenging and
haven't figured it out as feasible.
Ideally the rear cooling air  exits would be enlarged and the exhaust
exiting there, maybe an inch inside the cowl: excellent ground handling
cooling should be the result. The EZ's doing this are having no ill effects
from read of it.

Mark B. Magee
N34XL

Sent from IPhone 4S

On Sep 21, 2012, at 12:41 PM, Dave T Nelson <[LINK:
mailto:dtnelson at us.ibm.com] dtnelson at us.ibm.com> wrote:

I'm not going to debate this, but I stand by what I said and what dozens of
Long-ez and Varieze pilots and owners have experienced.  I would also note
that after hundreds of flight hours with this setup, I can confirm the lack
of any exhaust residue on the inside of my cowl.  Because I have a three
bladed MT prop, I do certainly get exhaust residue on the prop.  I've been
very careful to watch for any heat damage to the prop (the earliest sign
you'll get is a whiff of orange peels).  There has been none.

Please choose your own installation and focus on safety.

Dave

  1. Re:  Repairs (Scott Derrick)

----- Message from Scott Derrick <[LINK: mailto:scott at tnstaafl.net]
scott at tnstaafl.net> on Fri, 21 Sep 2012 08:42:56 -0600 -----

TO:
Velocity Aircraft Owners and Builders list <[LINK:
mailto:reflector at tvbf.org] reflector at tvbf.org>

SUBJECT:
Re: REFLECTOR: Repairs
 Hmmm.. I understand augmentation. but just ending the stack inside the
cowl, may augment a bit but the potential to get exhaust gas inside the
cowl is to great.

General to augment you have a tube inside a tube.  I don't see that.

If you look at the picture from the link below I first had the exhaust exit
without the forward bump on the cowl. I added the bump or flare in front of
the exhaust because the air was flowing into the cowling and defeating the
cooling.  Maybe if Lou built up a flare and tube for his exhaust to exit
through he could prevent exhaust gas form entering his engine compartment?

-------- Original Message --------
Subject: Re: REFLECTOR: Repairs
From: Dave T Nelson [LINK: mailto:dtnelson at us.ibm.com]
To: [LINK: mailto:reflector at tvbf.org] reflector at tvbf.org
Date: 09/21/2012 08:07 AM

Many EZ types have the exhaust end inside the cowl.  I've been doing that
for many years now on my Velocity.  It actually works quite well and can
increase overall cooling.  The exhaust gas is at such a greater velocity
than the air around it that  it actually acts as an augmentation and
"pulls" air out of the cowling.

Because your exhaust exits through the bottom of the cowl directly down
tangentially into the slipstream instead of exiting aft in parallel with
the slipstream, you probably are getting some of that hot exhaust gas back
into the cowl.

One other factor to consider is the large drag you are creating exiting
your exhaust down instead of aft.  It's a very "draggy" setup... I probably
gained close to ten knots when I got rid of it.

Dave

----- Message from Scott Derrick [LINK: mailto:scott at tnstaafl.net]  on Fri,
21 Sep 2012 07:18:20 -0600 -----

TO:
Velocity Aircraft Owners and Builders list [LINK:
mailto:reflector at tvbf.org]

SUBJECT:
Re: REFLECTOR: RepairsWow, I've never heard of ending he exhaust "inside"
the cowl! That sounds bad,  I definitely want my exhaust outside my engine
compartment and away form the plane!

here's a picture of my left stack.

Scott

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