Unclecoed bottom skin and center section aft bulkhead from center section asembly. Countersunk holes in center section assembly. [Inadvertantly countersunk holes for AN470AD4 rivets inaddition to those for AN426AD4 rivets. Received approval from Ken Scott at Van's support to use AN426AD4 rivets in lieu of AN470AD4.] Removed protective vinyl film, separated, and deburred skin attach flanges, skin stiffeners, and side bulkheads. Riveted skin attach flanges to center section assembly.
