REFLECTOR: Exhaust tips

Fri Sep 21 19:02:01 CDT 2012

y'all look at Jean Prudhomme's exhaust pics on the tvbf.org website under exhaust.

--- On Fri, 9/21/12, Mark Magee <edjonesbrady at gmail.com> wrote:

From: Mark Magee <edjonesbrady at gmail.com>
Subject: Re: REFLECTOR: Repairs
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Cc: "reflector at tvbf.org" <reflector at tvbf.org>
Date: Friday, September 21, 2012, 1:13 PM

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. MageeN34XL
Sent from IPhone 4S
On Sep 21, 2012, at 12:41 PM, Dave T Nelson <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 <scott at tnstaafl.net> on Fri, 21 Sep 2012 08:42:56 -0600 -----

To:Velocity Aircraft Owners and Builders list <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 <dtnelson at us.ibm.com>

To: 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 <scott at tnstaafl.net> on Fri, 21 Sep 2012 07:18:20 -0600 -----

To:Velocity Aircraft Owners and Builders list <reflector at tvbf.org>

Subject:Re: REFLECTOR: Repairs

Wow, 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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