Step 9.8, Aft top skins part 2

In the last posting I was unable to finish the aft top skins because I forgot to install the static ports. Here is the left port ProSealed and looking good.

So now I have to get serious about riveting the aft skins on.  The difficulty here is that the skins cover the top of the tail cone and the tail cone is not designed to have people crawling inside of it.  The first thing to do is make some kind of temporary floor in the tail cone to protect the bottom skin -- of the airplane and the person crawling inside.

Some plywood salvaged from the Van's fuselage crate is employed for the temporary floor.  A few cut outs to clear structure and the floor is ready.  The plywood is not resting entirely on the bulkheads though.  I placed blankets and pillows underneath to spread out the load across the bottom skin as well.

After installing the temporary floor I crawled inside to take a look around and found that is was not at all difficult to get in or out and it seemed to take my two hundred pound frame without complaint.

OK, time to get on with it.  The aft top skins having been previously prepared, are clecoed on. Then the rivets are placed and taped down so that they will not jump out when the riveting starts.

My helper has once again elected to buck, so she had to get inside.  She was a pretty good sport about it, only stopping once to request a pillow for her head.  Naturally, her request was denied and she was ordered back to work at once. Kidding, kidding.

I used up the last of my roll of rivet tape.  I've been mostly using masking tape on this project because of the expense for the rivet tape.  The rivet tape works much better.  I had actually forgotten how much better it really is.  I think for my next plane I will just throw caution to the wind and really splurge.  I'll buy two rolls of rivet tape.

Well, here it is.  Aft top skins complete.

Step 9.7, Aft top skins and static ports

There are two skins behind cockpit and one in front of it.  Our next step is get the two rear skins on before continuing on to the cockpit interior.  The skins are fairly thick as skins go, and require a significant amount of curvature especially near the tail.  This creates a lot of stress on the clecos when attaching the skins for match drilling because the skins would prefer to stay flat.  The process of attaching the skins will be very familiar to the reader at this point:  Match drill, debur, dimple, and rivet.

Before I could get to all of that I had to install the J-stringers at the top of the bulkheads.  Fortunately, I had already fabricated these when we were doing the stringers for the lower fuselage.  So it was just a matter of sliding them in place.

Match drilling

Debur

Well you get the idea.  Here's Carolina working the cleco pliers...

All of this excitement was too much for our puppy.

Now the skins are dimpled and ready to go back on for the last time.  It was about this time that I heard that now all too familiar sound effect of a record scratching in my head.  I realize that I hadn't installed the static ports.  If I don't to the static ports now I will have to crawl in the the tail cone do it later when it will be much more difficult.  Ordinarily I am predisposed to doing things the hard way, but this time I think I'll take the easier path.

Static ports? What are static ports?  I sense the readers unease as it would now appear likely that I am about to launch off in to another lengthy and oh so tedious discussion of airplane systems and/or history. Relax dear reader, this one will be brief: 

The static port on an airplane is used to measure the local barometric pressure.  This air pressure is then used by various aircraft instruments such as the altimeter and vertical speed indicator. The location of the static port is the most significant aspect of its installation.  It needs to be in an area of relatively undisturbed air in order to get accurate pressure readings.  In the RV's case, the static port is located on the fuselage side in between the wing and horizontal stabilizer.  OK, now I suppose you're thinking, I see what it does and where it's located, but what is it?  Well, that is simple. It's just a tube stuck out in to the wind. Perpendicular to the wind, actually.  So as not to induce ram air pressure.  The RV employs two static ports, one on each side of the fuselage which are connected together.  Having two ports allows the instruments to see the average of the two for a more accurate reading.

The static ports were located on the fuselage's side according to the plans, but I'm using SafeAir brand ports which have a wide base which requires the port to be moved about .25" forward to clear the F-708 bulkhead.

Here is the back of the static port showing the wide flange and the interfering bulkhead.

The inside surface of the skin and the SafeAir static port flange are roughed up and then cleaned while Carol heads to the kitchen to whip up a batch of our favorite.  Yes, it's time to get out the Proseal again.

The static port is bonded to the inside of the fuselage skin.

This is the Tee where the two ports come together.

And this is the static port from the outside.  Not much to look at, really.

 I will end this post here as it has become apparent that our dog Roxy is in need of another exorcism.

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.