06/16/2018 Horizontal Stabilizer – Fitted Inner Ribs (5.5 Hours)

Today I spent a couple hours on fitting the inner ribs (well I called them “inner” as they will be the most inner ones to the fuselage, right now on the left half of the stabilizer they are on the outside) HS-00005 and HS-00006 onto the skeleton and skin.

First I shape deburred all the edges of the flanges of those two edges to remove faceting. As to fluting, I only fluted HS-00005 a little bit and I left HS-00006 untouched because they are pretty straight already.

 

Once deburring and fluting are done. I inserted HS-00005 and HS-00006 into the left stabilizer. Clamped them to the skin and clamped the aft side of HS-00005 to the rear spar. Then I used the hole on the rear spar as a guide to drill and cleco HS-00005 onto the rear spar.

 

After drilling rear spar and HS-00005, HS-00005 is removed and I switch focus to HS-00006. First I need to use the pilot hole on HS-00006 aft flange as a guide to drill through the front spar and HS-00001 SB reinforcement plate behind it. Then the instruction casually says drill two more holes on the reinforcement angles that are on the same line of the those two holes on the flange. But if you look at the picture below, how in the world am I supposed to draw a straight line in that confined area blocked by skins on both side and mark the hole location 7/16 and 1/2 inch from top and bottom respectively? So I took the liberty to interpret that the instruction must missed the step of removing the skin and disassemble the skeleton.

 

After a round of removing the skins and disassembling to mark and drill two holes, I put the skeleton back together, including clecoing HS-00005 to the rear spar. Then I looked through the front spar and align HS-00005 front flanges center line behind the four holes I had drill in the previous steps. I clamped them firmly to maintain the position while putting the skin back on.

With the skin back on and HS-00005 aligned, it’s ready to match drilled HS-00005.

I drilled with #40 size pilot hole first before enlarging them to #30 size.

 

Like many people on Vansairforce forum during the horizontal stabilizer construction process, I have a hole that comes dangerously close to the edge distance limit. The top hole on my HS-00005 front flange(which was determined by a hole on the front spar reinforcement angle) is just a little over 0.220 inches(it’s somewhere around 0.220-0.250), slightly more than the 0.219 inch military specification limit for 1/8 inch size rivet hole.

 

The last item I achieved today is revisited a front spar trimming task that someone on the forum suggested to postpone when working on the front spar. The idea is that before the flange on inner front spar does not have the holes yet so it’s hard to determine the edge distance when trimming, it’s better to wait till the hole is drilled before trimming it. After finishing drilling HS-00005 and HS-00006 to the spars, I know where the hole will be already even though I haven’t drill the hole yet. So I marked the hole location with sharpie with the skin still on. Then I remove the skin and marked a very generous 2d radius around the hole, and with HS-00005 still attached to the front spar I drew the trim line.

 

It took me a few rounds of trimming with file and the bench grinder before I have enough material trimmed off on the spar’s flange so it doesn’t overlap with HS-00005’s flange anymore.