Joe Graham's Online RV-7 Builder's Log

Match Drilling The Horizontal Stabilizer

March 14-15, 2006

NOW I can finally start building some assemblies that actually look like airplane parts. Here is a photo of the left horizontal stabilizer skeleton. You can see the HS603 on the bottom and the HS702 on the top. Note the 6 degree bend on the inboard HS702 web. This looks like a rather trivial assembly, but each spar and rib component has been shaped, cut, marked, drilled, de-burred, countersunk, filed, sanded, and fluted. The plans state that most of the time spent in building this airplane is in preparing the parts for assembly. They are right! Pounding rivets is going to be the easy part.

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And here is a shot of the left and right HS skeletons.

Now it's time to match drill the skin to the skeleton. Here, I have clecoed the left HS601 skin onto the sub-structure. Note that the inboard ribs (HS404 and HS405) are not yet installed. These two ribs are not pre-punched at the factory. They are the last parts to be installed in the HS and are match drilled by using the skin as a template.

This is a picture of the HS404 (forward rib) and HS405(aft) as they were being fitted into the skin for drilling. I held the ribs in place using cleco clamps. These nifty little guys are operated using the cleco pliers and have pretty strong springs, so they hold things in place pretty well.

You can see in the previous photo and in this shot that the rib flange holes have not been drilled yet. Prior to installing the 404/405 ribs, I marked the center line of the rib flange along it's length. This mark then serves as the guide for aligning the rib to the skin holes, which are then used as guides for the match drilling process.

Here is the HS405 after match-drilling and clecoing in place. Note that the clamps have now been moved to the HS404 so it can be drilled using the same process. But before that can happen, the forward flange of the HS405 must be drilled through the HS702 flange, the HS710 and 714 angles, and the aft flange of the HS 404 rib. It's impossible to get the air drill in place at the correct angle with a regular bit because the drill body hits the HS 405 web. So a long bit is used, which minimizes the hole angle deviation from normal incidence.

Here's a close-up of the four difficult holes on the HS405 rib flange (now clecoed). This shot also depicts how the clecos work. See the following pictures for more detail.

If you look at the bottom of the previous photo you can see the lower HS405 rib flange with the cleco pins protruding through the holes from the bottom. The outer pins of the cleco are attached to the plunger on the top of the cleco. When the plunger is depressed, the outer pins slide forward and move together to form a smaller diameter, thus allowing the cleco pin to fit in the hole. When the plunger is released, the outer pins retract and are spread apart by the center pin, securing the cleco into the hole.

OK, enough Cleco school.... After match-drilling the left side of the HS, I did the same thing to the right side.

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