Chapter 23 – Left exhaust pipe tab

Yesterday I used a yard stick with a Sharpie taped onto the end of it to make a mark on the top cowling right baffle & reinforcement rib as a starting point for where it needed some trimming.

Today, after removing the top cowling, I started at that mark going forward to mark the right baffle rib for trimming (pic #1), and then trimmed it (pic #2).

After re-taping the outboard left exhaust pipe back into its proper position, and the left lower outboard exhaust pipe bracket mounting tab, I then mounted the top cowling back into place.

I have to say trimming the right baffle rib seems to have done the trick as all the front right corner fasteners went in fairly easily.  Moreover, the baffle seals are slowly conforming to the shape of the top cowling as each time the top cowling is mounted in place it’s going on just a little bit easier each time.

I also took a few minutes to sand down the outboard trailing edge of the right aft side of the top cowling where it intersects the aft inboard TE of the right wing, of which I’ve also been doing some fine tuning as well (marking while cowl on, then sanding/trimming when top cowl off).  I still need to finalize the cowl TE here, but I’m waiting until all the baffle seals are in and the exhaust pipes are secured internally to finalize this junction.

Of course the left outboard exhaust pipe hasn’t been welded up into it’s final configuration yet, nor have the exhaust pipes been trimmed to final length, but here is a current view of how they sit inside the aft left opening of the cowling.  Not bad, but they do tend to still point outboard a bit more than I want.  I’ll try to mitigate that a bit when I trim them to final length inside the cowling.

I thought I would add a shot of my chicken scratching plan that I drew up last night for today.  Of course while my mental meanderings can take a bit of time to get down on paper, I don’t often make it a practice to include them into these blog posts.

Now, my primary reason for putting the top cowling back on was to check the position of the left lower outboard exhaust pipe bracket mounting tab that is the focus of today’s efforts.  I had measured the proposed exposed drop of this tab to be 0.875″ from the bottom edge of the current aluminum baffle (“skirt”).

However, after both cowls were installed I realized that this measurement needed to be reduced in dropdown depth to just 0.6″.

With that bit of knowledge I then created the actual outboard tab/bracket (still blue at this point) and taped it into place inside the aluminum baffle aft corner.

I then connected the outboard 0.6″ marked line to the inboard bottom curved line of the bottom baffle edge (inboard of the inboard exhaust pipe) to get my downward angle of the tab going inboard.  I (quite cleverly… ahem!) used a magnet retriever to hold a 10-32 platenut in place to give an idea of what this bracket is all about (pic #1).  I then trimmed the corner tab to length (pic #2).

In a way installing this aft corner tab is atonement for another sin of the past, in that if I had had my exhaust pipe configurations truly dialed in, I wouldn’t have cut nearly as much of the bottom baffle corner away as I did.  Thus, I would have still installed an interior corner reinforcement bracket, but the original face (“skirt”) of the aluminum baffle would have been present.

But since it’s not, I had to resort to cutting out a corner fascia piece of 0.032″ thick 6061 to replace the material I had errantly cut away.  Here we have not only the corner fascia piece fitted and riveted into place, but the 10-32 (“K1000-3”) platenut and the corner exhaust pipe tab/bracket installed as well.

And a closer look at all that…

And a look from the left side at the side bracket securing rivets.

With the exhaust pipe bracket corner tab installed, I remounted the bottom cowling to check clearance… not too bad.

But since the lip of the top cowling overlaps the bottom cowling in this area, I had less than 1/16″ clearance with the top cowling mounted in place.  Clearly some trimming was required.

I reached into the cowling to mark the bottom corner of the exhaust pipe bracket corner tab for trimming (pic #1) and then refined the trim line after I removed both the top and bottom cowlings (pic #2).

I grabbed my trusty Dremel tool and carefully trimmed away the offending extra material on the lower edge of the exhaust pipe bracket corner tab.  I then threw a screw into the platenut just to reiterate the point visually that I installed the darn thing!

It was getting late, but I spent another 15 minutes making up a quick cardboard mockup of the lower left exhaust pipe bracket.  There will of course be a bracket on the top side as well that clamps the exhaust pipes into place on each lower corner of the baffles (with welded-in half tube “cups” compressing the exhaust pipes from top and bottom to secure them in place).

Hopefully this should help explain the purpose of the tab I just installed that will secure the left corner of the lower left exhaust pipe bracket, as there will be a screw securing each corner of the exhaust pipe bracket plates: 2 on the bottom plate (shown) and 2 on the top plate (4 total).  Again, as I casually mentioned, these exhaust pipe brackets are based fairly close to what Mike Melvill had on his bird.

And with that, I called it a night.  Tomorrow, after I finish designing and configuring my exhaust pipe brackets, I intend on getting the left aft baffle seals installed.  I’ll then repeat this process for the right side exhaust pipes and baffle seals.


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