Started Longerons

I started working on the longerons tonight.  First up is to cut them to length.  This is a critical cut because replacing these 15′ long angles would be very expensive (both in material cost and in shipping).  These need to be cut to precisely 173 7/16″.  Since the ends of tape measures can have some slop in them, a trick to get more precise measurements is to position the tape measure at the 1″ mark.  You do have to be sure to add 1″ to your measurement to account for this though.

These suckers are long.  They barely fit across my garage widthwise because of the stuff I have lining both walls.

I used my cutoff saw to cut these about 1/8″ long and then filed them to the correct length.

The aft ends of the longerons need some material removed.  I misread the plans at first that called for a 1/8″ radius and drilled a 1/8″ hole (1/16″ radius).  I fortunately had drilled the hole far enough away from the lines that I could file the radius to be 1/8″ and still not cross the lines (though it doesn’t look like it from this picture because of the burr around the hole).

Here are both ends cut and polished.

Next up is to lay out for the bends.  These lines define the forward end of the F-721 side rails and the point at which the longerons bend downward to meet up with the firewall.

The longerons are straight for the next 10+ inches or so, then curve inward to define the shape of the fuselage.

I placed marks every inch or so to help with the alignment during bending.

This is the rear end of the curve.  The longerons are straight from this point back to the tail.  It’s nearly midnight, so I’ll get started on the bending tomorrow.

Prepped, Primed and Riveted Bulkheads

The bulkheads have a bunch of separate flanges because of the tight radius of some of the curves.  Some emery cloth cut into 1/4″ wide strips works pretty sell when used like dental floss.

After a lot of sanding, cleaning and priming, the bulkheads are starting to go together.  Here, the F-705 bulkhead is clecoed together.  Double check that this bulkhead is square before riveting since the clecos allow some play in these pieces.  I could change the diagonal measurement as much as 1/4″ by racking these pieces from side to side.  After assuring that everything is square, this can be riveted together.  The blue tape signifies the holes that need to be left open right now since they will be riveted together with other parts of the structure at a later time.

Here is the F-705 bulkhead riveted together.  The clecos near the top are there because these pieces are riveted in conjunction with other parts.

This rivet needs to be a flush head since the seat belt attach anchor extends past this point.

Here is a closeup of the upper left portion of the F-705 bulkhead showing how many holes need to be left open for later riveting.

The upper seat adjustment pieces can also be riveted on now.  I used some rattle can primer on these so that I can easily remove it later when I’m ready for final paint.

The rear bulkheads are primed with epoxy primer and just need a few rivets each to join the two halves together.

The F-706 bulkhead is riveted along the bottom, but the top is left clecoed since it is riveted in conjunction with a top skin rib.

The F-711 bulkhead is riveted through the bars and around the lower curved section.  The upper and lower hole in each bar is left unriveted for now.

The F-712 bulkhead is riveted together using flush rivets on the aft side since the vertical stabilizer rear spar attaches here.

The F-728 and F-729 ribs that support the elevator bellcrank are attached and everything except for F-728 is riveted in place.

For fun, I clecoed the F-706, F-707 and F-708 bulkheads to the bottom skin to see how everything fits together.  The hole alignment is pretty poor.  The bulkheads will definitely need some fluting before everything aligns.

Upper Seat Back Adjustment

I drilled the upper seat back adjustment pieces.  None of these pieces have any layout holes, so everything has to be measured and drilled.

These pieces allow you to position the upper seat back in two forward positions by sliding the edge of part of the seat back into one of the two slots defined by these pieces.  Here, the seat back piece is positioned in the forward position.

Bent Upper Seat Adjustment

A couple of pieces of the upper seat adjustment mechanism needs to be bent to 4º.  I tried this without a brake and the bend was pretty poor.  I took advantage of the black friday sale at Harbor Freight to pick up this brake and made perfect bends in just a couple of minutes.

Finished Bulkhead Fabrication

I had the day off work, so my buddy Andre dropped by and we got started on the F-706 bulkhead.  First up is to drill some 0.063″ angle to a couple of support ribs.  Here is the rib that goes from the back of F-706 back to F-707.

And here is the rib that runs vertically behind F-706.

Here are how all of the pieces fit together.  The reason there is so much structure near the bottom of this bulkhead is that there is a bellcrank mounted here that connects the forward elevator pushrod (from the control sticks) to the rear elevator pushrod (to the elevator horns).  All of this is now match drilled.

Here is a closeup of this area.  The forward elevator pushrod passes through the hole visible here.  The bellcrank mounts between the two ribs near the top of the picture.

I also fabricated the straps that attach the horizontal stabilizer to the F-711 bulkhead.  Near the bottom you can see a taper cut into these to clear the side skin of the fuselage.

These are positioned against the front side of F-711 such that the bottom hole is 5/8″ up from the bottom edge and the top edge is 3 19/32″ from the top of the bulkhead.

These are then back-drilled through the bulkhead.

I drilled a series of eight holes along the inside edge of the F-708 bulkhead to attach the static tubing.  I also drilled holes in F-706 and F-707 (the two bulkheads forward of this one to pass the static tubing up to the front part of the fuselage.  There are also rudder cable holes in almost all of the bulkheads that require opening to 5/8″  With this, I think I am done with all of the drilling for the bulkheads (for now at least).  Everything can be disassembled, deburred, dimpled and primed in preparation for riveting.

Pitot/AOA Tube Routing

I used some self-fusing silicone tape to keep the two fittings on the pitot tube from rubbing against each other or the inside of the pitot tube mount.

I also used a MS21919-DG10 clamp to route the tubes towards the spar so that they don’t interfere with the aileron push tube.  The DG10 has enough free play that I can slide the tubing through it if I ever need to take the pitot out.  I’ll have quick disconnects in the wing roots that I can disconnect to create the slack to do this.

More Work on F-705 Bulkhead

I drilled the flap blocks to the sides of the F-705 bulkhead.  These won’t be bolted on until much later in the construction, but it’s easiest to drill them now.

I also drilled the four holes in the top of the two F-705G angles.

…as well as drilled and filed the elongated holes for the canopy latches.

I managed to get all of the holes in the F-705 bulkhead deburred.  I still need to finish the upper seat back adjustment parts, then this will be ready to prime and rivet together.

Worked on Rear Spar Bulkhead

I cut all of the pieces that form the upper seat adjustment.  I started to layout the holes, but I realized that my rivet fan won’t adjust wide enough.  Instead of doing this old-school, I’ll borrow a large rivet fan from a friend.

The lower bulkhead needs a couple of 5/8″ holes for snap bushings to run wires through this area.  Edge distance to the adjacent holes is right at the recommended amount.

The F-705D uprights need 5/8″ holes as well for the rudder cable snap bushings as well as a couple of K1000-08 nutplates each.  I installed these before priming because I’m only going to prime parts now that won’t get a top coat of the interior color.  I’ll also probably use self-etching primer for all of the cabin components so that I can easily wipe off the primer at some point in the future if I need to paint an area.

Rear Spar Bulkhead

My buddy Andre stopped by today to give me a hand with the rear spar carry-through bulkhead.  First up is to shoot the two rivets I couldn’t do easily yesterday.  I didn’t get a picture of it yesterday, but I also riveted on the main spar uprights.  A few of these rivets could be squeezed, but most needed to be shot and bucked.  I’m definitely getting the hang of doing that solo.

The rear spar bulkhead starts with a could of beefy pieces of 2024-T4 bar stock.  The lower one in this picture runs all the way across the bulkhead and carries the major portion of the load.  Shorter pieces of bar stock with a couple of bends in them are riveted to these to create a socket which will receive the rear wing spar.

The lower seat belt attach points are drilled and bolted to the rear spar carry through structure.  The technique here is to mark and drill one side that then clamp the other side in place with a 3/16″ spacer.  An AN3 bolt is exactly 3/16″ thick, so clamping one of these between the anchors creates the perfect spacing.  The holes in the top of the anchors (off the top of the picture) are held in alignment with an AN4 bolt.  The other anchor can then be back drilled through the spar.  You can also see here the outboard seatbelt attach points require the anchors to be cut to clear adjacent rivets.  Here, the left anchor has been cut, but the right one is still full size.

Here are all four seat belt attach points match drilled to the spar.

The shorter spar bars are tapered for weight reduction.  You need to make sure that the last rivet has 1/4″ edge distance all around the radius.  By positioning this end first, I could easily ensure that.

Then the other end can be cut flush with the long spar bar.

While I was working on the rear spar, Andre fabricated the upper angles that will receive the canopy latch pins.

The angles fit behind the upper portion of this bulkhead.  I drilled the four corner holes so that I could use rivets to keep the three prepunched pieces in alignment.  The angle could then be clamped in position and the holes match drilled.  I’ve said it before, but these self-adjusting clamps absolutely rock.