REFLECTOR: turning the exhaust exit

Sun Nov 25 17:23:24 CST 2012

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 
  To: Velocity Aircraft Owners and Builders list 
  Cc: Velocity Aircraft 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 <velocityxl at fastmail.fm>
    To: Velocity Aircraft Owners and Builders list <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 <michalk at awpi.com>
        To: Velocity Aircraft Owners and Builders list <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" <richard at naples-air-center.com> on Thu, 22 Nov 2012 08:00:21 -0500 -----
                  To: Velocity Aircraft Owners and Builders list <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 <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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