REFLECTOR: turning the exhaust exit

Mon Nov 26 09:21:45 CST 2012

This is impressive! It still seems to me that a collector for each pair
would be more efficient. What is the reason for not having a 4 into 2 setup?

I would like to see how others with six or eight cylinder engines have
designed their exhaust systems to reduce drag. Has anyone done this for a
Franklin?

Grover McNair

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Douglas Holub
Sent: Sunday, November 25, 2012 6:23 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: turning the exhaust exit

The straight pipes. They are ceramic coated, and I put some aluminum tape on
the cowl near the pipes as a heat shield. The cowl doesn't get hot, and when
the propeller is installed at the correct clock with respect to TDC, I get
very little soot on the propeller. 

Doug Holub

----- Original Message ----- 

From: Mark Magee <mailto:edjonesbrady at gmail.com>  

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

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

Sent: Friday, November 23, 2012 11:56 AM

Subject: Re: REFLECTOR: turning the exhaust exit

All,

I still don't understand why the exhaust isn't shot out the rear cooling air
exit holes as done on a Long EZ. The newer Long EZ's have the tips slightly
inboard of the cowl exit for scavenging: no issue with drag and possibly
better ground cooling. Ceramic internal coating of the exhaust greatly
reduces the radiated heat from the pipes. As well heat shields can easily
and inexpensively be installed. If the exit holes were opened up, I would
think this setup would be ideal. 

Any configured as such?

Mark B. Magee 

Sent from IPhone 4S

On Nov 23, 2012, at 10:04 AM, Scott Derrick <scott at tnstaafl.net> wrote:

I ended up painting that lower cowl 3 times!  ;-)

I used Custom Aircraft Parts in San Diego for the exhaust.  He sent me the
90's, I cut, fit and marked the pieces, sent them to him for welding, and
had them back in 3 days. I had him put in a 1/2 nipple on one side for the
air breather tube at the same time.  No more oily streak after a long
flight!

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: turning the exhaust exit
From: Velocity  <mailto:velocityxl at fastmail.fm> <velocityxl at fastmail.fm>
To: Velocity Aircraft Owners and Builders list  <mailto:reflector at tvbf.org>
<reflector at tvbf.org>
Date: 11/23/2012 08:21 AM

Thanks for the picture I like what you have done. I will try it also . One
reason I keep telling my self 
why I have not painted my plane yet still experimenting!

Ron

On 11/23/2012 9:11 AM, Scott Derrick wrote:

It does work, 

I think I increased my top end by 3-5 knots by adding the 90's to my
exhaust. I have 3-into-1's, one on each side.  See attached photo.

The ramps in front of the exhaust exit on the cowl were to prevent air from
entering the lower cowling through the two holes(port & starboard) and thus
reduce my cooling by raising the ambient lower cowl pressure, they also
worked well.

I don;t think you loose 10 knots by straight down exhaust, but you do loose
something.

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: Reflector Digest, Vol 92, Issue 64
From: Brian Michalk  <mailto:michalk at awpi.com> <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list  <mailto:reflector at tvbf.org>
<reflector at tvbf.org>
Date: 11/23/2012 07:27 AM

I've heard the 90 degree exhaust so many times, but I can't help think that
its an old wives tale.  Does anyone have any research that describes the
phenomena?

Logically, it doesn't make any sense to me that it should be a problem with
drag.

On 11/22/2012 09:40 AM, Dave T Nelson wrote:

Hi Richard.  Your friend is exactly right - you do need to have slip joints
of some type on each cylinder of your exhaust.  You should also check to
make sure that they are free to move - I do that as a part of my preflight.
If you don't, any exhaust will eventually fail, and it can go through the
prop.  That's not true of just "in the cowl" exhaust systems - that's true
of every exhaust system.  A safety of some type is also a requirement of any
exhaust on a pusher.  Remember - you have to consider anything aft of the
firewall as a direct threat to your prop and make sure it's safetied...

I had the two into one exhaust exiting the bottom of the cowl for awhile.
The drag penalty was 8-10 knots.  Shooting the exhaust straight out of the
bottom creates a huge plume of flat plate drag....

Happy Thanksgiving!

Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering

  1. Re:  STG-RG Performance (Richard J. Gentil)

----- Message from "Richard J. Gentil"
<mailto:richard at naples-air-center.com> <richard at naples-air-center.com> on
Thu, 22 Nov 2012 08:00:21 -0500 -----

To:

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

Subject:

Re: REFLECTOR: STG-RG Performance

I had the help and advise of a long time builder who had built several EZ's
among his long list of aircraft. 

I was thinking of a EZ style exhaust for my SERG but he recommended against
it because of complexity. 

His primary concern was that you need springs, brackets, hardware, etc to
hold the exhaust in place and many an EZ owner have had those part break off
and go right through the prop. 

For that reason I went with 2 to 1 exhausts that I cut flush with the bottom
of my cowling safety wired to the engine mount. 

With as fragile as MT props are I wanted to eliminate as best as possible
anything going through the prop. 

Richard 

Sent from my iPhone 5

On Nov 21, 2012, at 9:31 AM, Dave T Nelson < <mailto:dtnelson at us.ibm.com>
dtnelson at us.ibm.com> wrote:

Hi Grover, 

Yes, you absolutely need to be concerned with your prop - anything and
everything that can affect your prop you should be concerned about!  In this
case, I am a follower, not a leader.  I'm still very connected with the EZ
crowd (I built a Varieze first and flew it for many years).  The EZ guys
were the first to try this kind of exhaust.  Prop heating is for sure the
biggest concern.  

For the first hundred hours I flew this exhaust I very carefully monitored
it for any signs of degridation.  There are specific things you look for
(surface cracks, a distinctive "burnt orange" smell, etc.).  I have had no
issues (200 - 300 hours on it now).  

I'm certainly not recommending this to anyone - I'm merely showing what I've
done and sharing results.  Your results may vary.  

After many years and hours of use now, the biggest problem I have with this
setup is that a three blade prop can't be clocked to avoid the exhaust
pulse, and so I get soot on the blades.  I've found that "goof off" is the
best at removing the soot.  

I haven't observed any paint coming off the prop at all.  Yes, it's an MT
(MTV - 18B (if memory serves)).  I'd have to check, but I believe there's
maybe 8 - 10 inches or so from the exhaust exit to the prop blade.  

Good luck - let me know if you have questions.

Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering

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