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  #21  
Old 06-13-2018, 07:49 PM
vetterman vetterman is offline
 
Join Date: Oct 2006
Location: TX
Posts: 39
Default Exhaust

The intent of the original question was directed at A models whereas the nose gear A frame and exhaust pipes occupy much of the exit area-plugging up the exit area. By moving the pipes outward which is only @ 4 inches it opens up that crowded area. The redesign of the current crossover system for vertical sump setups reduces both crossover bends from 105 degrees to 90 degrees. Simple to do during fabricating a system.
One more note of interest. The turndowns offered as an option for the RV-8 only do to the tunnel design and exhaust pulsing on it.
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  #22  
Old 06-14-2018, 08:10 AM
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DanH DanH is offline
 
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Location: 08A
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Quote:
Originally Posted by dtw_rv6 View Post
Would it capture the intent of your design if I were to shell out the existing outlet bump? That would eliminate the large flat area on my exit plug. Or are you implying that the exhaust tubes need to be much further apart (as in straight down from the cylinder ports)? My glasswork isn't necessarily pretty, but I'm working on it. The real issue for me would be custom exhaust fabrication.

However, now that I'm thinking of it, that might make for a very clean exit path for the cooling air -- straight back and down.
Larry and I think so too.

It's not really a design, but rather a concept. If developed further, yes, I would shrink the inlet scoop body as much as possible, and remove all of the outlet "coal shovel", leaving the least possible bump fairing for the nose gear.

Quote:
Originally Posted by vetterman View Post
One more note of interest. The turndowns offered as an option for the RV-8 only do to the tunnel design and exhaust pulsing on it.
That would be another case of your design desires being compromised by stock airframe considerations. Swapping the aluminum ramp for a one piece SS ramp, then damping the backside of the ramp and the first belly panel allows a slash cut tailpipe. Best way to damp the rearmost rivet in the floor stiffener (the one that cracks the skin) is to drill a .25" hole in the floor just above it and inject a small blob of Firebarrier 2000 into the enclosed space.
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  #23  
Old 07-11-2018, 08:17 AM
Pittsartist Pittsartist is offline
 
Join Date: Aug 2013
Location: UK
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Quote:
Originally Posted by Zazoos View Post
Vetterman Crossover Exhaust on an 0320 with a 0360 scoop. In the following 3 pictures you can see the exhaust tips point towards one another. The closer the tips point towards one another the greater clearance I have at the exit from cowling. The picture with the tips furthest apart have about 1/2 inch clearance to the cowling at the exit.

I was thinking the exhaust would point more straight back. Am I missing something or does this look correct?

I appreciate the input.


Here's my aircraft - I0-320 with Vetterman x over. (the centre pipe is the Christian "overboard" pipe)

[IMG]_MG_0715 by WIGY TV, on Flickr[/IMG]
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  #24  
Old 08-05-2018, 03:13 PM
dtw_rv6 dtw_rv6 is offline
 
Join Date: May 2008
Location: Martinsville, IN
Posts: 349
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Okay, finally getting around to making my prior plug a little better. I haven't downloaded my EFIS data for hard data comparison, but I am definitely feeling a difference in climb performance with the plug I made versus without. This modification should cut down on the frontal area drag also.


Concept:


I just started on the actual modification today. I ran out of water and time today, so I'll do layups tomorrow night. Hopefully it won't be 100F outside then

Cut the existing cowl:


Inside view:


Roughing in the formers:

Last edited by dtw_rv6 : 08-05-2018 at 03:16 PM.
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  #25  
Old 08-23-2018, 08:07 PM
dtw_rv6 dtw_rv6 is offline
 
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Location: Martinsville, IN
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I'm seeing a minimum of a 5 knot increase with my modified cowl exit:


Next step is a set of aft exit ramps to re-attach the air to the fuselage:


Now for the part that makes me dizzy. I'm plotting about 2 hours worth of data from my EIS - manifold pressure on the x-axis, and TAS/RPM vertically:

Pre-modification:


After lower cowl mod:


This is just from me flying around tuning my autopilot and some local burger flights, so I didn't get enough samples for all manifold settings. All I did was sort the data (high to low) for MP, and then for RPM. The large spikes are the periods of climb and descent, while the gentler sloped areas give me a rough idea of the airspeed for level cruising.

For the curious, I'm running a Catto designed for a 190hp engine on my 180hp Superior. Note how the RPM and airspeed numbers go flat after about 24" on the old cowl, while they tend to increase with MP in the second graph. Less drag / more speed. I'll likely send the prop for a re-pitch this fall if I can't get enough RPM with drag reductions alone.

Last edited by dtw_rv6 : 08-24-2018 at 06:10 AM.
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  #26  
Old 08-23-2018, 09:15 PM
crabandy crabandy is offline
 
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Location: Ottawa, Ks
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Oh Doctor!
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  #27  
Old 08-24-2018, 07:17 AM
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grubbat grubbat is offline
 
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Default Pics

Carl, any pics of the side exhaust?
Craig

Quote:
Originally Posted by Carl Froehlich View Post
Have side exhausts on the six cylinder Franklin RV-8. A lot of power, looks good, sounds good and hard to get CHTs above 360.

Carl
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RV-3 Sold
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C-140 In a barn
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J3-65 Cub - low and slow stuff
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  #28  
Old 08-24-2018, 08:21 AM
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DanH DanH is offline
 
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I can't find any useful conclusions in the data as presented. Don, got anything that compares TAS for same MP at same altitude, in level flight? Forget RPM.

Quote:
Note how the RPM and airspeed numbers go flat after about 24" on the old cowl, while they tend to increase with MP in the second graph.
The flat look is just graph scaling. Two-thirds of the Y axis only covers a MP spread of 0.7".
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  #29  
Old 08-24-2018, 09:41 AM
Mark33 Mark33 is offline
 
Join Date: May 2010
Location: Baton Rouge, La.
Posts: 378
Talking

Quote:
Originally Posted by dtw_rv6 View Post
I'm seeing a minimum of a 5 knot increase with my modified cowl exit:


Next step is a set of aft exit ramps to re-attach the air to the fuselage:


Now for the part that makes me dizzy. I'm plotting about 2 hours worth of data from my EIS - manifold pressure on the x-axis, and TAS/RPM vertically:

Pre-modification:


After lower cowl mod:



This is just from me flying around tuning my autopilot and some local burger flights, so I didn't get enough samples for all manifold settings. All I did was sort the data (high to low) for MP, and then for RPM. The large spikes are the periods of climb and descent, while the gentler sloped areas give me a rough idea of the airspeed for level cruising.

For the curious, I'm running a Catto designed for a 190hp engine on my 180hp Superior. Note how the RPM and airspeed numbers go flat after about 24" on the old cowl, while they tend to increase with MP in the second graph. Less drag / more speed. I'll likely send the prop for a re-pitch this fall if I can't get enough RPM with drag reductions alone.
Don,

I think the graph that you have pictured is really showing yourself hooked up to an EKG. Iím seeing some ST segment elevation and I think you may be having a heart attact due to you being so excited flying your airplane. My recommendation is that you slow that thing down and go get checked out by your Dr. LOL!!
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  #30  
Old 09-09-2018, 06:03 PM
dtw_rv6 dtw_rv6 is offline
 
Join Date: May 2008
Location: Martinsville, IN
Posts: 349
Default Looks like I was fooled..

Dan,

I had to look through lots of engine monitor files to find matching altitudes and manifold pressures, but I did manage to pull it together. No fancy graphs for us this time, but I'm no longer convinced that there is a measurable difference in speed between the stock cowl exit and my modified version. CHTs, absolutely hotter. TAS, not so much.

I''ll be cutting it back off next weekend.

Don
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