Step 9.0, Installing the steps

On the tricycle gear version of an RV airplane, the RV7A in my case, the fuselage sits fairly high off of the ground.  A little bit too high to comfortably step up for ingress.  So the steps are added just behind the wing to permit a middle step between the ground and the top surface of the wing.

I didn't take any pictures of the steps before I drilled the flanges, but I wanted to include a shot here to show the whole step to put the following photos in context.  As a first step, (pun intended), I laid out the locations for the holes in the flange.  The flange sits on the outside of the skin and the pipe section shown below going from middle to left in the first photo, attaches inside the plane at the baggage floor ribs.

Typically, the flange is riveted to the skin, but I wanted to make my steps removable since they are prone to cracking.  To make them removable I need to drill the flanges for 8R8 screws.  I'm also counter sinking them to improve their appearance.

The 1/8 and 1/16 markings on the flange indicate the measured curvature required at that location.  More on that later.

A plastic block is drilled to receive the end of the pipe.  The block is bolted to a baggage floor rib.  A few additional holes are drilled in the plastic for rib attachment bolts and for a bolt that captures the end of the pipe.

The next step is to test fit, and it is noted that the flat flange does not follow the contour of the curved fuselage.

Both vertical edges and the lower edge require a beat down with a hammer to fit the fuselage.

Now that the flange fits fairly well it's time to match drill the flange to the skin.  Although the pictures show the flange already counter sunk, at this stage the flange was only drilled to #30 so that the match drilling would accurately locate the screw holes in the skin.

With the screw holes are drilled, the nutplate retaining rivet holes can be located and drilled with a nutplate jig.  Not all of the holes were drilled at the time of this photo.

After all of that the steps are temporarily clecoed on so I could admire the progress.  Upside down, they don't make much sense to Trina.  It's hard to impress a puppy.

Step 8.9, Center section to tailcone assembly

Now that the center section bottom skin is riveted on the baggage compartment floors are temporarily attached (foreground) as well and the seat skins (background).  The F-705 bulkhead is in the middle of the picture below.  Recall that the 705 bulkhead supports the seat backs.

The next step is to insert the upper longerons into the tailcone.  Here one can see the curve that was so lovingly bludgeoned into the aluminum angle in Step 8.5.  There is a slot cut into the bulkheads such that the longerons may pass by on their way to the tail and its depth just allows the outer surface of the longeron to be flush with the bulkhead flange, allowing the skin to lay flat across both.

Now the big step is flipping the center section and tail cone upside down and setting them on saw horses. Naturally, this does not go as smoothly as it seems it should.  First I discover that the center section is too wide for the saw horses.  If I had taken 2 seconds to think about this before it lifted the piece up it wouldn't have been any big deal.  But I didn't, and now I have to find a way to wrestle this thing safely to the ground.  I am the master of empirical discovery.  Did I mention that I was attempting to do this by myself?

OK. Now I've got some wood on top of the saw horses to make them wider and once again I gather my strength and undiminished resolve to lift the center section into place.  It's really not all that heavy, it's just a bit wobbly.  From underneath, the two spar verticals have to set on the sawhorse in front while the middle sawhorse holds the forward most bit of the tail cone.  The only thing holding the center section up is that it is leaning on the front of the tailcone.  It sets there very precariously until the center and tailcone can be clecoed together. 

At this time I would like to point out that the tailcone and the center section have no intention of being joined. There are overlapping skins, and baggage ribs, and various other points of contention.  One by one they must each be addressed before the two will join.  In order to get to that point, however, the whole assembly must be alternately pushed and pulled, and jostled about while at the same time keeping it from falling off the the sawhorses.  Some profanity may have been emitted.

As soon as the center section skin is clecoed to the bottom of the tailcone the side skins are temporarily applied.  I say temporarily because as soon as they are clecoed on, the build manual has you taking them right back off to bend the lower curved section that meets the center section skin. 

And so the curved bit is a cone shaped affair that turns 90 degrees to meet the bottom skin. A piece of angle is match drilled to the tab to keep the end straight and then a good deal of force is applied.  Eventually, a nice smooth curve will appear.  Stop bending when the curve is a right angle at the small end and sweeping 90 degree turn on the other.

When the curve is satisfactory, the skin is returned to the airframe.  At this point the side skins can be match drilled to the bulkhead and spar center section.   In addition, the longerons are drilled to match the side skins. 

Meanwhile Carol has been working diligently to fabricate the myriad of small flanges, spacers, and attachment straps that are used in the fuselage assembly.  

She was hoping to avoid the paparazzi.

In the next posting we attach the steps.

Step 8.8, Center section assembly

Now that the center section ribs are attached to the spar carry-through the rest of the center section can be fit.  The principal components involved are the F705 bulkhead, the baggage compartment floor ribs, and the center section skin holding it all together.  So exactly where on the aircraft is the center section?  Well, the center section lies roughly in the middle of the fuselage,  ha ha.  To be a bit more precise, the pilot and passengers sit on the ribs between the spar carry through (gold) and the F705 bulkhead.  Their knees go over the spar while and the seat backs rest against the bulkhead.

The first thing is to collect all the pieces, mainly the ribs and the already completed F705 bulkhead.  The dark grey thing pictured below is one of the access steps.

The F705 bulkhead is clecoed to the seat ribs prior to riveting.

The two combined are flopped over a sawhorse and the center section skin is clecoed on for match drilling.

After all the holes are drill they must be deburred.  I find the angle drill makes fast work of this process, but it takes a light touch.

One of the more difficult aspects of building your own airplane or any project of this level of complexity is the requirement of making decisions early in the build process that have ramifications later on.  Some are bigger than others of course.  Like choosing a tail dragger vs. tricycle gear, or a tip up canopy vs. a sliding canopy.  Very often these decisions are irreversible or nearly so, and this aspect just adds to the anxiety of the decision making process.  In any case, all of the things not decided for you by the kit manufacturer are your responsibility as the builder, and quite naturally require a good deal of research.  I find that when I feel like I'm not making good progress it is invariably because I can't decide on some small issue and I'm just dragging my feet.  

And so it goes that there steps that protrude from the fuselage side to aid in climbing up on the wing.  And it seems that these steps are prone to cracking after some time.  Many builders have reported online of the rather involved process of repairing or replacing them.  One of the major impediments of repairing a cracked step is that they are attached to the plane's baggage floor ribs underneath the baggage floor, which is riveted down.  Thus, the repair first involves drilling out all of the floor skin's rivets.

An alternative to permanently fastening the baggage floor with rivets is to use screws and nutplates in their stead. So my big decision this week is whether or not to take the time out to add the 40 or so nutplates required to make the baggage floor removable.   Meet the nut plate:

This particular model is a dimpled nutplate for an 8R8 screw.  Using a dimpled model allows the use of a counter sunk screw which, in turn, allows a flat baggage compartment floor.

Meanwhile, Carol cranks out many of the small flanges and other assorted do-dads that hold the plane together while Trina looks on innocently.  Notice the plans draped over the dimple machine and the back of a chair while drying.  The result of a mishap involving the exuberant puppy and bottled water.

When all of the center section holes are deburred they are then dimpled.  My DRDT-2 dimple machine gets a good workout on this sheet.

 The rivet lines are primed.

Now its time to assemble the baggage compartment ribs

With all of the center section ribs in place the center section skin can be riveted on.

And that's about it for the center section.