Chapter 2 - Fabricating the Tail

Section 1 - Installing the Nut Plates

Jig for Drilling Nut Plate Holes

Nut plates are used throughout the tail construction to attach the hinges and the weldments to the fiberglass structure.  The photo above shows how a simple fixture can be used to speed the drilling of accurate holes in the nut plates.

Start with a

Nut Plate Parts

There are two sizes of nut plates used in the construction of the horizontal and vertical stabilizers, one uses a K1000- 4 nut plate and one uses a K1000-5 nut plate. Both of these are secured to the aluminum plate with xxxxx rivets.

Completed Nut Plates

When installing the nut plates there are several important points to keep in mind:

  1. The hole through the spar should be drilled over sized so the bolt can move around allowing proper positioning of the hinge.
  2. Insure that you are putting the nut plate on the correct side of the spar.  One side had two extra layers of fiberglass applied, this is the side for the nut plate.  This should also be the side you have marked the location of the horizontal stab ribs, as seen above, since this will be the inside of the stab.
  3. When installing the nut plates on the Horizontal stab spar it is important to get the hinge bolt dead center of the spar.  Use a set of calipers to achieve this as seen below.
  4. When installing the nut plates on the Elevator Spar it is not only important to get the hinge bolt dead center of the spar, but also to insure the spacing is correct to match the spacing of the horizontal spar hinges.  This is actually easy to do, as you will bolt the eyebolt side of the hinge to the rod end side and use the horizontal spar as an adjustment fixture for the elevator spar.
  5. Once you have mounted the nut plates for the elevator spar (this is done later during the assembly of the elevator), you must mark the left and right elevator spar sides as they will differ slightly.

Install Eybolt or Rod End to Secure Nut Plate

Here we are using the calipers to insure the eyebolt is exactly centered on the spar.

Installing Nut Plates

To install a nut plate with pop rivets:

  1. first properly locate the hole as above.  It is best if the hole is slightly oversized. 
  2. Thread the eyebolt into the nut plate, insuring one last time you have it on the proper side of the spar.
  3. Drill a single #30 hole through the single layer of fiberglass using a hole in the nut plate as a guide. Do not drill all the way through the spar (if you do, not to worry). Install the first pop rivet once you are happy with the alignment of the plate. 
  4. Finally, drill the remaining three holes and install the final pop rivets.



Installed Nut Plate

Looks Good.

The elevator hinge eybolt will be installed later. For completeness, a couple of photos are included here to give you an understanding of the hinge design. A large washer and a steel spacer are installed under the eybolt, and the eyebolt is tighted down against the spar. It is the clamping of the eybolt with this steel spacer that transfers the loads of the elevator to the horizontal stabilizer. Look again at the photo above. the nut plate is attached to the skin of the spar with four pop rivits. If the steel spacer and washer are not installed, these rivets will be the only thing holding the eybolt in place. WARNING: IF YOU DO NOT INSTALL THE WASHER AND STEEL SPACER AS SHOWN BELOW, YOUR ELEVATOR HINGE WILL FAIL, AND YOU WILL DIE! Sorry to be so melodramatic, but this is an extermely important point.

Eye Bolt with washer and spacer




Properly installed eye bolt in horizontal stabilizer