I’m happy to announce that, at least as far as this Long-EZ build, today is a rather historic milestone. After well over a year and a half of working my cowling vs exhaust pipe issues, both of these have been essentially solved. Especially since today I finally trimmed both sets of exhaust pipes to length!
Ok, starting out I pulled the crankcase vent tube Batman cradle/insert Version 2 off the 3D printer and test fit it on the pipes. There was still just a hair too much play at the bottom of the “V” so I added 0.012″ to each side of the gap and reprinted this insert.
Here’s a shot of the approximate location of the 2 aft cradles, which will secure the crankcase vent tube in between the 2 right side exhaust pipes. The single pipe “saddle” will be on the outboard pipe at about the very right edge of the pic below.
I wanted to trim the exhaust pipes after I had a chance to get the exhaust pipe brackets welded up by my Über-welder buddy James, but I know he’s busy and I wanted to get these pipes cut. I doubt that the bracket configurations are going to change more than a few thou one way or the other, so I’m pressing forward.
I started on the left, port side. Now, what I’m dealing with in trimming these exhaust pipes is that I’m not just cutting the ends 90° in the vertical and 90° in the horizontal… not that that’s not exactly what I would prefer to do!
As I’ve noted before, since these pipes have a final curve outboard when looking from the top, and the upward angle of the pipes as they approach the aft cowl opening looking from the side, leads me to leave a bit more pipe on the exit top edge and angle the exits inboard in an attempt to shoot the exhaust straighter aft (vs up) and inboard towards the prop hub.
I took a while —using a measuring tape, yardsticks, plumb bob, and laser level— to dial in the cut angles that I wanted (pic 1), at which point I removed and cut the outboard pipe (pic 2).
With the outboard exhaust pipe to my desired angles, I then used it to verify the cut line for the inboard left exhaust pipe. I then removed the inboard pipe and trimmed it to length.
Here we have both left exhaust pipes cut and trimmed to their final length and exhaust angles.
Before moving onto the right side exhaust pipes, I quickly mounted the bottom cowling to verify that the left side pipes were good.
I also checked the distance between the end of each left side exhaust pipe and the aft edge of the lower cowling: about 1.2″ for the outboard pipe and 1.4″ for the inboard pipe. I discuss the difference from the left side in the regard as compared to the right below.
Also before I started on the right side exhaust pipes, I grabbed some coffee from the house and Version 3 of the crankcase vent tube Batman cradle/insert off the 3D printer. Yep, I think this one is the dawg that will definitely hunt! I’ll start working my plan to machine these saddles/cradles/inserts up on the mill.
On the right side exhaust pipes I pretty much followed the same exact process as I did on the left side: verify the final length and angle of each pipe before marking them for trimming (pic 1). And then removing the outboard pipe to trim it first (pic 2).
Here we have the right side exhaust pipes —and thus ALL the pipes at this point!— trimmed to the length and angle to get the best exhaust flow out of the cowl as possible.
Here’s an initial shot of the both trimmed exhaust pipe pairs. And yes, the right side pipes sit considerably lower than the left side pipes. Also, the right side pipes are situated just over 1/2″ further outboard than the left pipes.
I wanted to get an idea if I would actually need to bend the very aft end of the crankcase vent tube, so I slid it into place… of course checking how the Batman cradles would work out as well. I’ll need to do a little bit more R&D on the aft bend (I want to be able to get it through the exhaust pipe bracket nub for maintenance without having to bend it back straight).
I then mounted the lower cowling to check out the clearances and how the trimmed exhaust pipes looked in relation to it.
Again, due to the location of the very aft bend on the right side exhaust pipes, and since they are over 1/2″ further outboard than the left side pipes (these right side pipes are as far inboard as they can physically go), to get a decent exhaust angle as inboard as possible (read: pretty much straight aft) I had to trim them farther forward of the cowling trailing edge than on the left side. Thus, the right outboard exhaust pipe end is about 1.6″ inside the cowling while the inboard pipe is about 1.8″ —centerline of pipe, while the very inboard edge is almost 2″ (pic 1).
I’ll note that on the left side pipes, due to the aft bend, I would have had to trim much further forward to get past the bend to make any real effect on the exhaust. This would have resulted in the exhaust pipe ends being around 2.5″ to 3″ inside the cowl… just not worth it (pic 2).
And finally, here we have the trimmed exhaust pipes sitting in both the mounted top and bottom cowlings. Nope, they’re not perfect, symmetrically or stunning in their presentation… but again, I think they’ll work functionally without burning up the cowlings or the prop. Certainly not bad considering the starting point on these cowlings and pipes.
Pushing forward!