Step 9.6, Aft deck plate and gussets

At this point the fuselage is like a cardboard box with no top.  Like an open box, the main longerons can move forward or backward relative to each other and this movement will cause a twisting of the fuselage.  In order to prevent this the main longerons are tied together at the rear of the fuselage using the F-714 aft deck plate.

Before the longerons can be locked together by the F-714, any pre-existing twist in the fuselage must be removed.  The first step is to level the fuselage horizontally across the two longerons at the F-705 bulkhead which is just behind the seats.  This is near the widest point on the fuselage and it will make the measurement much more sensitive to have a longer distance measured.

The second point to be measured is at the rear of the fuselage over the F-714 aft deck plate (blue).  If the fuselage is level at both points, it is assumed to not have any twist.  So with the deck plate in place, the fuselage is tweaked as necessary to bring both points measured into level and the deck plate is match drilled to the longerons.

The fuselage is checked for level one last time before the now primed aft deck plate is riveted on.

Here is some more structure that holds the vertical stabilizer on and is also an elevator stop.

Next on the to do list is the F-757 gussets.  These two parts tie the F-705 bulkhead to the main longerons.  They require some layout to locate a square hole in the middle.

I cut the hole to the sides with a step drill and used a #30 drill for the inside corners.

A little bit of filing and we've got a square hole.

Here is the part in place.  Over the F-705 bulkhead and under the longeron.

The F-721 side rails are next.  These were previously trimmed and match drilled so there is nothing to do but rivet them on.  They strengthen the top of the center section and provide a flat surface for the canopy to close against.  Shown below, F-721 at the top and the arm rest in the middle.  At left, is the F-705 bulkhead.

It's a nice quiet Sunday afternoon in the shop, the racket of the occasional rivet being driven not withstanding.  I couldn't help but stand back and admire the progress so far.  It's beginning to look like an airplane!

Back to work now with the F-695 gussets that tie the main longerons to the firewall.

And finally, the shoulder harness anchor points are attached to the longerons.

There are gussets on the F-706 and F-707 bulkheads.  The purpose of these gussets is to maintain the web of the bulkhead's channel construction perpendicular to the surface of the skin.  The bulkhead is very rigid in the direction parallel to the web (towards the center of the fuselage), but not strong at all in any other direction.  So the gusset restrains the bulkhead from twisting under stress into a less strong geometry.

This is the view aft.  It doesn't have much to do with anything in this posting.  I just like the picture.

Next time we'll start the aft top skins.

Step 9.5 Flipping the canoe

In the last posting I was just finished with the lower half of the fuselage's exterior.  Since the fuselage is upside down on the saw horses, and since it somewhat resembles a canoe, the RV builder's community refers to this milestone in the aircraft's construction as "Flipping the Canoe."

At this point I have a choice on how to proceed.  I can flip the canoe over on to the saw horses and be done with it, or I can build a giant rotisserie to hold the fuselage at any angle -- flipped or not.  Those of you who know me, or who have at least read the previous posting, will understand that I am not one to take the simple road if a more complex solution exists.

And so, rotisserie it is!  Here is the basic frame.  The frame rests on neoprene leveling feet that really grab the floor.

The most difficult aspect of the rotisserie are the bearings.  I am far too impatient to order bearings and then wait for them to be shipped. Paradoxically, I am not at all opposed to spending endless hours fiddling with some home-made contraption.  Luckily, this time out, my first attempt came out really well.  I found two pipes in the steel dealer's cut-offs pile that would nest fairly well.  When I got home I found that there was about 60 thousandths slop between them.  I found a piece of .025" aluminum in my scrap bin and rolled it up and gently persuaded it into the pipe with a mallet.  That leaves about 10 thousandths slop.  If I were building a space shuttle, I guess I would have tried for 5 thousandths.

The aluminum doesn't go all the way around.  I left a small gap where the pipe's welded seam goes through. The thickness of the aluminum is just about the same height as the seam so what remains is a nice bearing surface for the inside pipe to ride on.  With a little grease it turns freely and with a very pleasant silky smoothness too.

With the bearing problem solved, the next step is painting it so as not to offend my aesthetic sensibilities.

Out of the paint booth and ready to attach to the fuselage.

And here it goes.  The fuselage turns over like the Poseidon Adventure in reverse.

I'm still working out a brake like device that will allow me to position the fuselage securely at any angle.  Until then, I've just drilled a hole through the axle assembly to permit me to pin it in the horizontal position.

The canoe is flipped.  Now, what's in the fridge?  Hmm.  Something in the upper left, I think.

Step 9.4, Forward fuselage reassembly

It was very disheartening to see all of that work going away as each piece was disassembled.  Conversely, now that the pieces are going back together, this time permanently, the mood is much lighter.  After all of the priming and deburring it's very nice to get back to assembly.

Before I assembled the forward bottom skin to the center bottom skin, I need to test fit the landing gear weldments and match drill them to the side skins.  There is an interference with the spar carry-through flange which must be ground away before the weldment will sit flat against the spar.  Pictured below is the trimmed area before final filing and polishing.  The cut gets very close to one rivet, but it is unavoidable.

After that, it was just a matter of reassembling the pieces which were all carefully marked with their part number and an arrow indicating their proper orientation, i.e., forward, up, left, or right as required.  Since there were no parts to make this time around, the reassembly via cleco went very quickly.  Please enjoy the following musical montage sans music:

When the firewall is attached to the side skins the joint is first sealed with a fire resistant silicone.  This is designed to prevent exhaust gases from entering the cockpit.  It has the added benefit that should the engine catch on fire, neither the passenger or nor the pilot will be inconvenienced by the smell of smoke.

Before the bottom skin is riveted on, the lower longerons are bolted to the engine mount weldments on the back of the firewall.

In this spectacular photo, the camera on it's own, decided the table top was the more interesting subject.

I didn't take many photos of the riveting process because Carolina and I were both involved.  For most the the process Carolina was under the plane because she prefers to buck rather than shoot.

I like that photo because she is smiling.  In the future I will show her that picture and gently suggest that this phase was not as bad as she remembers.

 

One of many long evenings of riveting is done.  Mercifully, it's time to go back up to the house.  

All together, it took a couple of weeks to complete this reassembly.  There are hundreds of rivets in the side and forward bottom skins and along the center to tail cone joint.  I can't say that this portion of the project was a lot of fun, just that it sure is nice to finally move on.

One of the really amazing things that the reader will not readily appreciate is the way the structure becomes very robust and unyielding as the rivets go in.  It really is a wonderful thing to watch as the flimsiest of materials quite suddenly take on a strength that would be unsuspected to all but the structural engineer.

So, at this point the lower half of the fuselage is mostly complete.  Enough of the structure is riveted together that the fuselage can now be self supporting.  This means the fuselage can be turned over in a process known to builders as "Flipping the Canoe."  Since the bottom of the fuselage is not flat, most builders construct some kind of cradle to hold the fuselage and to raise it to a comfortable work height.

Some claim time and effort savings if a giant rotisserie is constructed to allow the fuselage to rotate to any comfortable angle which will facilitate access.  My motto has always been "If there is a way to save time, I'll do it no matter how long it takes."  Here are a few shots to get the flavor of this little side project.  The rotisserie is made primarily from rectangular steel tube, 2" x 1", a little bit of .75" square tube, and some 1" angle.

In the next posting the canoe will finally be righted, the rotisserie will be demonstrated, and the death march toward riveting madness will be a distant memory.

Step 9.3, Forward fuselage disassembly

Well after all of the apparent progress on the fuselage framing, its time to take a few steps back, lest we finish too early.

So as we have seen in previous postings, the build order is temporary assembly, match drill mating components, disassemble, prime, and finally reassemble.

So the pieces have all been match drilled and now they come apart.  I like this view because with the side skin off, it resembles a cut-a-way drawing.

Going,

Going,

Gone!

So sad to be back here again, but its all necessary so that we can debur, dimple and prime.  Here are the forward longerons -- deburing in progress.

One row dimpled and one to go on the side skin to tail cone interface.

Most of the longerons are too thick to dimple, so they must be machine counter sunk.

Here is the main longeron in process.  I guess I should have made my shop bigger.

And at this point I discovered that I failed to match drill a couple of holes in one of the longerons.  Since I already had the skins off there was nothing to locate the hole's locations without reassembling the longeron to its mating side skin.  Fortunately, I remembered reading about this happening to another builder who used his other longeron (which had the holes) as a reference to locate the missing ones.  After clamping the two back to back the whole calamity was quickly averted.  Here is a photo with the longeron ready to be drilled.  The missing holes were in between the two sets of clecos.

Nut plates being attached to the back of the side skins to attach the steps.

And thats all he wrote.  Well, not quite. I'll finish this posting by noting that the reader has been spared the life threatening tedium of  a lot of pictures of the seemingly endless parade of deburring and dimpling that followed the teardown.

So to recap where we are:  All of the forward fuselage frame, from the tail cone to the firewall, has been disassembled, deburred, dimpled and primed.  In the next post, Carol the riveter returns as she helps me to permanently reassemble the newly prepared pile of parts.