If you have not already, read Part 1 of this project here
Since I really had no idea what to expect with version 1 of the exhaust, I did not 3D model a darn thing. I grabbed my TIG torch, eyeballed the tubing alignment, closed my eyes and tack welded the tubes in place while hoping for the best. I would either have a decent prototype or a horribly failed experiment, both outcomes leading to a good story someday.
After just a few hours testing the prototype stub stack exhaust I knew the design had enough potential to start drawing a proper 3D model for a version deux.
Fresh off that positive testing, I knew I needed a real 3D model to allow for a few things:
- First, it would allow me to visualize various bend options quickly without having to cut up and tack expensive 304 stainless steel
- If needed, I could 3D print various designs to mock install on the actual powerplant
- Most importantly, a 3D model would allow me to create a jig so I can weld up identical parts
For this project I am utilizing standardized 304 stainless fortyfive degree bends and exhaust tips. Using standardized bends does limit my design possibilities slightly, but for this simple exhaust design they are absolutely perfect. Like pie-cuts, these bends are identical within reasonable tolerances which makes it much easier to fab identical parts in an assembly line fashion.
The most important first step is to 3D model the individual stainless components as close as possible to allow an tight jig fit.
Queue the 3D scanner!
Armed with a low quality scan and a set of dial calipers, I can accurately dimension a part and match the digital model to the unique curves and angles of the stainless component.
The below is the V1 tear drop exhaust tip (which I will be using again on the V2 design) with the native model and 3D scan side by side:
Although not always necessary, I will often 3D print the individual components to make sure the dimensions of my 3D model accurately reflect the stainless version. The first print looked good at first...
...but after closer inspection it became obvious the height was off by ~.100"
After a quick model change and a quick reprint, the printed exhaust tip matches its stainless steel counterpart:
With various 45 degree bends, exhaust tip, and an expander cone accurately modeled, I can now play with various combinations of these parts in digital space.
I like the "tight" tucked-in look of the prototype exhaust:
Unfortunately the first few hours of flight testing showed the lead buildup on the lower pilot-right firewall would quickly get out of hand with the tucked-in exhaust. For the version 2 design I wanted to push the exhaust tips further out into the slip stream.
With that in mind, the V2 design quickly came together:
This new design may not alleviate the leading problem inherent to this short stubby exhaust, but it is worth a try.
Armed with an accurate 3D model ofthe new design it is now possible to model a jig. The jigs only job is to consistently align each component for tack welding.
With a 3D model of the V2 jig, there is only one thing left to do - make it real in plastic!
In the next installment of this project I will weld, install, then test this new V2 design.