Rough and Ready Aerospace: Step 3.2, Rudder frame

Purpose

This is a blog containing the build history of an experimental home built airplane. The RV-7A is a two place, piston powered, low wing, tractor configuration, tricycle gear, aluminum and composite aircraft. The original purpose of this blog was to document the construction of my experimental category aircraft in order to satisfy the build log requirement for the FAA. Now it's just for the amusement of friends and family as I document some of our aviation experiences. For more information on the RV series of aircraft see www.vansaircraft.com.

Thursday, March 8, 2012

Step 3.2, Rudder frame

The rudder frame consists of the spar, lower rib and two upper ribs. There is also a milled piece of angle called the rudder horn just below and behind the bottom rib shown below. To get to this point a shim is fabricated to space the rudder horn such that its top end can slide in over the bottom rib's end flange. If this isn't perfectly clear, it wasn't to me either. A considerable period of staring at the plans failed to crystallize the correct order of assembly in my mind so I just picked up the pieces and played with them a bit. Thinking, how would I design this, or more to the point, if X needs to get done, how can these parts make it happen. Well, when you just start putting them together the answer usually just pops right out immediately. As it did in this case, and I'm left wondering why I wasted so much time staring at the plans. Returning to the plans, the exploded view provided makes perfect sense once you already know the answer!

Counter balance rib and lead weight

After sorting out that puzzle, the next step is to flute the tip rib and the counter balance rib. It seems that when the ribs are manufactured, the process bending a three dimensional shape from a two dimensional piece of sheet aluminum leaves them warped lengthwise. Fluting, refers to the straightening of the ribs by judicious application of small bends in the rib flanges. These bends take up the 'extra' length in the flange that causes the bowing of the rib. There are a variety of pliers made to make these bends -- ranging from a sharp v to a smooth semicircle. I like the semicircle one.

Here is the tip rib fluted. Once you think the rib is straight, it is a simple matter to test your work by aligning the rivet holes with a straight edge.

Blah, blah, blah. Back to the frame assembly. Shown below is the tip rib and counter balance rib along with the counter balance skin all attached to each other and the spar.