REFLECTOR: Reflector Digest, Vol 92, Issue 64

Kevin Baker flykb at verizon.net
Thu Nov 22 19:53:51 CST 2012


Any idea why folks don't go ahead and do a 90 deg pipe after exiting the cowl on the bottom instead of straight out ?
With 8-10 Knts ... That's significant 

Thanks
Kevin Baker

.

On Nov 22, 2012, at 9:40 AM, Dave T Nelson <dtnelson at us.ibm.com> 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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