Work Continues On F-1294A&B Tailcone Fairings

Must say, the F-1294A&B tailcone fairings are beginning to turn into a time sucking abyss. This has become one of those tasks that, although not hard, has seemingly taken far longer than expected to accomplish.

The first task of the day was to enlarge the #40 holes drilled yesterday in the F-1294A upper fairing. The plans call for taking a #27 drill bit and purposely destroy the cutting edge by drilling a 1/8" hole into concrete to create a “modified” #27 drill bit.  Yes, you read that right … drill concrete with the drill bit before using it. Sounds easy enough right?  Well I’m here to tell you I could not get the drill bit to go much farther than 1/16", even tried a couple of spots … the hangar’s concrete floor is seemingly diamond hard. My best guess is that the whole point of using the “Modified” drill bit is so it does not shred the fiberglass or try to dig into the fiberglass to rapidly.

The modified #27 drill bit is to be used to enlarge the #40 holes in the F-1296A upper tailcone fairing and on into the F-1294C tabs. The reality of it is, I was able to easily drill through the fiberglass but the drill bit was so dull it just would not penetrate the F-1294C tab even with quite a bit of pressure applied. So I changed gears and just used the "modified" #27 drill bit to drill through the fiberglass and moved onto the next hole. After all the #40 holes in the fiberglass were drilled with the modified bit, the modified drill bit was exchanged for a normal #27 bit and the #40 holes in the F-1294C tabs were easily enlarged to #27.

Using the “modified” #27 drill bit to enlarge the #40 hole in the F-1294A upper tailcone fairing.

At this point, the instructions have the builder remove all the F-1294C tabs and rivet nutplates onto the tabs.

Using the pneumatic rivet squeezer to rivet a nutplate onto one of the F-1294C tabs.

After the nutplates are installed, the tabs are Clecoed back in position on the F-1294B fairing and the F-1294A upper fairing is now screwed in place. (A bunch of washers were placed on the screws so they could be tightened without needing to be screwed in a mile deep).  After the upper faring is screwed in place the plans have the builder mark and create a gap 1/32” to 1/16” between the F-1294A&B tailcone fairings. This became a little time consuming because I actually had the fairings sitting tightly together so had to slowly create the required gap by sanding , testing the fit then … repeat … repeat, etc.

The F-1294A&B tailcone fairings screwed together and the required gap has been established.

After the required gap is acceptable, the two rivet holes in the F-1294B lower fairing that secure the F-1294C tabs require countersinking for flush AN426AD3-3.5 rivets. When riveting the F-1294C tabs onto the F-1294B lower fairing it is preferable to not set the rivets fully so the fiberglass does not get crushed.

Using the machine countersink cage outfitted with a #40-100 degree bit to countersink the rivet holes in the F-1294B fiberglass fairing.

Riveting the F-1294C tabs onto the F-1294B lower fairing with AN426AD3-3.5 rivets.

All F-1294C tabs riveted in place. Note one can easily see the rivets my finger is pointing towards are not fully set when compared to the rivets above them securing the nutplate. This is OK when riveting fiberglass, as it helps keep the integrity of the fiberglass.

The next step (other than permanently mounting the fairings) is to enlarge the slot in the fairing. However, it was pouring outside and not wanting to make the necessary cuts inside the hangar, will complete this task during the next work session.