Brief Description: Assembly of Center Section Bulkhead
The Center Section bulkhead is the "anchor" part of the "floor" of the RV-12. The first part was installing 4 nutplates on the Center Bulkhead. A retainer block was affixed to the center bulkhead.
TheCenter Section Aft Bulkhead was clamped to the center section bulkhead and supported by two bolts holing it up level with the center bulkhead. The aluminum "skin" that will eventually be the bottom of the fuselage was clecoed to the center and aft bulkheads, and the clamps loosened to allow the parts to better align, and then the clamps were retigtened.
The 72 pre-punched 1/8th inch holes in the aft bulkhead were now used to guide the drill throught the heavy extruded eluminum piece that is the anchor of the Center Section Bulkhead. This is called "Matched Drilling". Matched drillinig is used to make the holes match up better, or to use one set of holes to guide the drill into another piece of aluminum.
Two holes were then enlarged to a #11 size and a row of the matched drilled holes were Machine Countersunk. Machine Countersinking is a process of scooping a funnel shaped hole around a pre drilled hole. This is usually done so that a flat head rivet can be set flush with the surrounding metal This is helpful if another piece of metal needs to be placed flush against the riveted piece, or to rivet outer skins with flush rivets so their is less drag. Less drag results in faster flying speeds and/or more miles per gallon of gasoline.
I'm not yet sure of the purpose of these counterunk rivets It may be because the gas tank will flush up to the edge.
Next came attachment of aluminum pieces that will be used to attach other structures to the Center and Aft portions of the center bulkhead.
The next chore was to fabricate and install two stiffeners to keep the skin from flapping while flying. It was difficult for me to understand the drawings that I was supposed to emulate. Finally it became clear to me that the ddrawing was incorrect.
I called up the builder assistance at Van's to alert them to the erro
