Category: 4 – Fuselage

Now I proceeded to drill all of the remaining holes (except the ones for the F-706 bulkhead and the F-718 longerons) to final size.

I checked with  DWG 27A for the position of the F-792 rudder stop. I had to leave one hole open to match with the drilled hole in the rudder stop. I marked this hole so that it would not be riveted or dimpled.

When drilling was complete, I removed the skins. I then deburred the structure and the skins, dimpled as required, and clecoed the rear fuselage back together.

Time: 4 hours.

With all the skins in place I checked to make sure there was no twist in the fuselage by hanging a plumb bob on bulkheads on each end. The tooling holes are on center, so if the plumb line fell past the center of the top and bottom holes, on both bulkheads, the fuselage would be straight. I double-checked this before I drilled.  I double-checked the J channels for proper position and drilled them to the skins. It worked best to drill every fourth or fifth hole and then cleco. I worked from one end to the other. When the J-channel was located, I drilled the remaining holes.

Time: 2 hours.

Now it’s beginning to get interesting: putting some of the big assemblies together. I began by setting up three sawhorses so they were all at the same height and level.

I began the assembly by clecoing the F-779 Tailcone Skin to the F-711 and F-712 bulkheads as shown in drawing 26. I laid the F-778 Aft Bottom Skin across two of the sawhorses, with the outside surface down. I then reached underneath and clecoed the F-707 and F-708 bulkheads to the inside of the skin. I marked the outside face of the lower 4 J-channels with a lengthwise centerline. I slid the lower 4 J-channels into the slots in the bulkheads, leaving them loose.

I then slid the assembly to the edge of the sawhorses and clecoed the F-773 side skins to the bulkheads. I clecoed the F-706 bulkhead to the assembly and the F-729A bellcrank rib to the bottom skin. I then added the F-711/F-712/F-779 assembly and clecoed in the F-710 bulkhead.

Time: 6 hours

Finishing the J-Channel

I cut the F-786A, B, & C J-channel to length and prepared the ends as shown on DWG 18.

Time:  1 hour

I began by finding the AA6-125 longeron angles which were shipped in my wing spar box.  I then measured and trimmed them to the correct length.  I trimmed the horizontal face on the aft end of the angle as shown on Detail C, DWG 18.

I was bending a left and right version of the F-718 longeron. To avoid confusion I marked the angles as left and right longerons and specified the front, rear, top and side.

I laid the longerons side-by-side on the floor with the ends matching and marked the starting and ending point of the shallow curve, looking down. This bend follows a line 0.032” inside the outside edge of the F-721B Aft Canopy Deck.  I marked the location of the sharp downward bend, in side view. This bend occurs at the front end of the F-721 B.

Bending the Shallow Curve

I bent the F-718 longeron angle in my sturdy vise mounted to my solid, stationary table.  I padded the jaws to protect the longerons from gouges and scratches.

I held the angle in the vise, pulled on the free end and established a small “pre-load” on the angle and then gave it a small-to-medium whack with a rubber hammer to produce the bend. I made several small, progressive bends to form the curve.

I cut the template from DWG 17 and glued it to a piece of stiff cardboard. This served as my guide while bending the longeron. I made both sides useable so it would work on both the left and right longeron.

I clamped the angle in the vise so the end of the jaw was one inch aft of the aft mark. I started bending at the mark.  I then pushed the forward end of the longeron in the correct direction, held it there, and hit it right at the end of the vise jaw with the rubber mallet until it bent a few degrees. I moved it an inch and repeated the process until I got to the other mark.  I checked it often against the template to prevent overbending.

I kept coaxing the angle until it matched the curve of the template. I could clamp the angle in a six-inch vise without removing any of the bend, so it was easy to add more bend.

I remembered to check that the angle had not bent out of plane (up or down) as I was applying the sideways load – it is quite common to get vertical bow while bending a horizontal curve.  When this happened,  I rotated the longeron 90, clamped it in the vise and bent it back straight with my hands.  I called it a night when the curve of the F-718 longeron matched the curve on the template within a 1/16″ all around and the angle sat flat on the table within a 1/16″.

I taped a piece of 0.032” aluminum to the outboard surface of the longeron and fit the F-721B aft deck to the top of the longeron.  I carefully established the fore/aft position.  The shim simulated the F-770 side skin. When the outside edge of the side rail matched the outboard surface of the shim, I drilled the F-721B to the longeron. I left it clecoed for the time being.

Making the Sharp Downward Bend

The front of the F-718 longeron needed the sharp bend and twist to be applied. The bend was done using the same method as the curve; I just didn’t move the longeron. The angle really wanted to curve off axis on this bend.  I checked this bend by using the F-770 forward side skin as a template.  The angle matched the upper portion of the skin within about a quarter of an inch.

Twisting the Forward End of the Longeron

I applied the twist with a big crescent wrench.  I clamped the longeron in the vise, with the point of the downward bend at the end of the vice jaw.  I then grabbed the end of the angle and gave it a twist.  I kept going until I had the twist shown on View A-A’, DWG 18.

Time: 6 hours

The F-712 is also a double bulkhead and again F-712A is the front and F-712B is the rear. They needed to be riveted together before the fuselage was assembled. The flush rivets were used with the flush side aft. The aft surface has to be smooth so the vertical stabilizer spar will fit. For the RV-7A, the aft tiedown was to be fitted later, in assembly with the vertical stabilizer.

Time:  6 hours

After the usual preparation, I riveted the bulkheads and bars together to form the finished F-711 Bulkhead.

Time:  1 hour

The F-711 is a double bulkhead. The front half is F-711A and the back half is F-711B. The protruding F-711C bars will attach to the horizontal stabilizer. The F-711C bars are tapered for the RV-7A.

I marked the centerline of the F-711C bars and clecoed  the F-711A&B bulkheads together, using the holes that were not common with the bars. I then clamped the bars against the F-711A forward bulkhead, with the lines showing in all the pre-punched holes, and then drilled them using the prepunched holes as a guide.

Both F-711 Bulkheads had the upper portions trimmed away to allow the elevator pushrod to pass through.  I trimmed them to the marks on the bulkheads.

Time:  2 hours

The F-707 and 708 bulkheads are simple two piece bulkheads. I aligned the tooling holes and riveted them together.

Time: 1 hour

I fit and riveted the F-706A-L&R bulkhead halves to the F-706B bulkhead bottom. I left the top joined with clecos. I then drilled and clecoed the F-728 channel to the pre-punched location hole on the top of the F-706A bulkhead.

Time: 1 hour