Lots of progress made on the horizontal stab today.

Today's progress consisted of five small but separate operations:

- Locating and drilling the horizontal stab front mount brackets
- Finishing the holes on the forward spar end brackets
- Locating and drilling holes to attach the upper and lower doubler to the rear spar
- Locating the drilling holes to attach the rear ribs to the rear spar
- Locating and drilling holes to attach the two full ribs to the rear spar

Locating and drilling the horizontal stab front mount brackets

After puzzling for a while about these brackets and whether or not it might be possible to use existing holes in the upper and lower doubler (of the forward spar) to fasten the brackets to the forward spar, I finally realized that the flanges of the brackets point outboard, not inboard. This puts the row of rivets well between the existing holes.

Once I realized this, it became very obvious that it would not be possible to use the existing holes in the upper and lower doubler, so I quickly resigned myself to drilling the five holes which are needed. I made the top and bottom of the five holes in line with the upper and lower doublers, then equally spaced the remaining three in the web of the forward spar.

My method for ensuring that the mounts are square--and this is the same method I'm using for all the bits and pieces that mount square to the spars--is to locate the top hole, drill and cleco it, then use it as a pivot to align the piece. Then I drill and cleco the bottom hole, recheck for location and square, and drill the in-between holes.

I followed this same procedure for both brackets, and that was that.

Finishing the holes on the forward spar end brackets

When I made these brackets, which eventually connect to the full ribs as they extend from the rear spar, I didn't know at the time exactly how many holes to drill between the top and bottom holes, which are in line with the rivet line on the upper and lower doublers.

Turns out that the brackets need four holes total, so two needed to be located and drilled; this was easy to do with the rivet fan. I clecoed the bracket into position, marked the locations, and drilled them through the bracket and the spar. This process was repeated on the other side.

Locating and drilling holes to attach the upper and lower doubler to the rear spar

Locating and drilling holes to attach the upper and lower doubler to the rear spar was probably the largest single operation I got done today. I started by laying out the parts, as I usually do, and then I found the centerlines of the spar and the two doublers.

It's easy to make little mistakes--I measured the full length of the rear spar and found it to be 2220 mm, and then I marked the center as 1010 mm. That's a hundred millimeters short. I realized the mistake when I eyeballed the centerline and found myself thinking "Boy, that doesn't look much like the center...."

Once the centerlines were marked, the next thing to do was to mark the spar with lines at 120 mm and 160 mm from the centerline on each side. Then I marked a rivet line on the doublers and used the rivet fan to mark rivet locations starting at 120 from the centerline and pitching 40 mm all the way to the ends--this put the last hole 10 mm from the end of the doubler, just as it is supposed to be. Then I put one additional rivet location on each end of each doubler 20 mm from the ends--this put it exactly halfway between two rivet locations already marked using the fan.

Once both doublers were marked for rivets, I clamped the upper one in place and started drilling and clecoing. My general method is to drill and cleco a location inboard, then go far outboard--in this case, I went all the way to the last rivet location--and drill and cleco that one. Then I drill one about halfway between those two, cleco it, and then drill and cleco every third one between them. After that, I drill the remaining holes.

I did this for both doublers, and that was that.

Locating the drilling holes to attach the rear ribs to the rear spar

The next operation involved confirming that the 160 mm lines I drew on the rear spar were, in fact, 160 mm from the centerline of the spar. They were, and I noted that the rivet holes which were located using the rivet fan from the 120 mm spot fell right in line with the 160 mm line, as they should.

Next, I used the rivet fan to mark two spots for rivets on the 160 mm line between the top and bottom rivet holes already drilled, and then I drilled these two holes in the spar.

Next, I drew a sight line on the rear flange of both the rear ribs; these pieces already had holes drilled on their forward flanges, which matched to holes on the forward spar. I positioned the rib so that I could see the line which I drew on the rear flange through the holes on the 160 mm line on the rear spar, and checked the general squareness of the rib; it looked okay to me, but just as I did with the ribs-to-forward-spar connection, I drilled and clecoed the top hole first and used that hole as a pivot to square the rib perfectly against the rear spar.

After confirming that the rib was square to the spar, I drilled and clecoed the bottom hole, checked again for squareness, and then drilled the two holes between the ones already drilled and clecoed.

I followed this same procedure to connect the other rear rib to the rear spar. Easy.

At this point, I connected the ribs to the forward spar to produce something that somewhat resembles an aircraft component--very exciting.

Locating and drilling holes to attach the two full ribs to the rear spar

Since I had the forward spar connected to the rear spar, it occurred to me that it I may as well connect the two full ribs, which go on on the rear spar at the ends of the doublers.

What I did was place the full rib in its position, flanges pointing outboard and curved side to the bottom of the assembly, with the web right up against the ends of the doubler. Then I drew along the outboard edge of the rib's rear flange--this meant that when I removed the rib from the rear spar, I'd have a way of knowing exactly how far the rib's rear flange extends from the ends of the doublers toward outboard.

I removed the rib and then drew a vertical line centrally between the ends of the doubler and existing outline of the edge of the flange--this became the line on which four rivets would be located.

Then I marked four holes for rivets on this centerline--the top and bottom I made level with the rivet line on the upper and lower doublers, and then the two holes between were marked using the rivet fan. I drilled these four holes.

Next, I put the full rib in place and sighted through the top hole to find the line I drew on the rear flange. I drilled and clecoed the top hole, used it as a pivot to square the rib, then drilled and clecoed the bottom hole. I rechecked square and then drilled the two in-between holes and repeated the process for the other rib. Easy.

Finally, I saw that a corner of the end brackets, which are attached to the ends of the forward spar, poke up past the curved surface of the full rib where it touches up against the bracket. That was to be expected.

Since trimming this small corner seemed to be a quick and simple thing, I marked the amount that needed to be removed using the curve of the full rib, removed the end bracket, rough cut the material away with snips, and used a steel file to clean it up. Then I reattached the end bracket and confirmed that the edge now conformed to the curve of the full rib.

That was all I had time for today--I cleaned up and put up, and spent about three hours on it today.

Slideshows documenting all this to come later.