Tuesday, December 9, 2014

Starting the wings

Well, despite best intentions to update the blog a little more regularly I see a month has passed since my last update.  Was sidetracked by a number of things over the last month, but did manage to hit some significant milestones and have have made a nice start on the wings.

Big event of the last month was the arrival of the wing kit, which also came with the replacement elevator skin I needed.  The guys at The Airplane Factory made taking inventory of the wing kit a breeze - only a couple small questions came up that will be easily resolved.  One thing that was apparent from the start was that the pieces are getting bigger, and there is a lot more of them!

Following inventory, I deburred and primed the replacement elevator skin and finished up the elevator (other than the tips).   Moment of truth came when I mated the elevator to the horizontal stabilizer and was relieved to see that the hinges lined up perfectly and that the elevator swung freely.  Whew!

With that done, the empennage parts were set aside and I started on the ailerons and flaps. Process was pretty much the same as for the empennage components - test fit the parts and make any required adjustments to ensure proper final fit, followed by deburring and prepping for priming.  One new technique I got to try out on the flaps was fluting.   When I initially did a test fit of the flaps I was dismayed to see that a few of the ribs did not align well with the pre-drilled holes in the skin.  On closer inspection, it was clear that the reason for the poor fit was that a couple of the ribs in each flap had a pretty clear  bend in them.  After scratching my head about it for a bit, I remembered that I had purchased a set of fluting pliers specifically for situations like this.  A minute or so with the fluting pliers on each rib fixed the problem - ended up being quite a painless issue. A little more prep work and the flaps will be ready for priming as well.

Both elevator skins riveted
Rudder mated to the vertical stabilizer in the background, and elevator mated
the horizontal stabilizer in the foreground

The rivet pail is getting low - guess that means the empennage is nearing completion!
Wing spars (in the wood box) and all other components of the wing skeleton
All the wing skins and the wing tips
Checking the fit of the aileron components
Aileron components deburred, cleaned and ready for priming
Checking the fit of the flap components
One of the flap ribs that needed fluting - a few other ribs
 had a bigger bow to them than this one.
Trial fit of both flaps

Friday, November 7, 2014

Empennage Nears Completion

Another long overdue posting, but certainly progress has continued despite a number of work conflicts over the last few weeks.

Continuing from the last update, the top rib of the vertical stabilizer with the VOR puck was riveted to the skeleton.  RG-400 cable was passed through grommets in the ribs and secured.  Wiring for the rudder strobe was also run through the grommets. A few hours with a rivet gun later and the vertical stabilizer skin was riveted on, completing this piece.

Riveted vertical stabilizer frame showing the RG-400 run for the VOR
and the wiring run for the rudder strobe
After riveting the vertical stabilizer, I once again joined it to the rudder and ensured that the rudder swung freely and that there was no interference with the VOR elements.

Rudder swings freely without interference from the VOR elements

Next up was the elevator.  Although the elevator is the first item for completion in the empennage plans, I had waited until the end to start it due to the skin that was accidentally damaged earlier in the build.  As with the other pieces, the elevator build started with riveting the skeleton together.  The elevator spar was a little more complex than some of the other pieces, but overall went together smoothly.  Once the skeleton was complete, I riveted the right skin on,leaving the left side ready for riveting once the new skin arrives. After I complete that, attaching the composite tips on the elevator and rudder will complete the empennage.
Elevator spar in progress. Torque seal on the nuts indicates that these nuts have been properly torqued.
Tape marks holes that are not to be riveted until the skin is attached. Note that I also ran bolts through the holes wherever I could prior to riveting to help ensure the holes lined up after setting the rivets.

Elevator skeleton riveted and ready for the skins. Note the counterweight on the end rib.

Right elevator skin riveted
Right elevator skin again

Monday, October 6, 2014

I Have Airplane Parts!!!

First step after my last update was to put together the skeleton of the horizontal stabilizer.  Once that was riveted, I temporarily attached the skin and test fit the rudder and vertical stabilizer - they fit together quite  well and all it took was a simple light finger touch to turn the rudder on the bearings.  While they were attached, I tested out the anticipated attach points for the VOR antenna to ensure they did not interfere with the rudder swing.

The Technical Counselor paid a visit last week to observe my work so far.  After inspecting the work and talking through a few hints and tips, he gave me the go ahead to close the skins on the horizontal stabilizer and the rudder.  With this approval, I riveted the second side of the horizontal stabilizer to completely finish it, and also riveted the second side of the rudder skins to get it ready for the next step.

That done, I moved onto the installation of the VOR antenna in the horizontal stabilizer.  The VOR antenna is not part of the standard kit, so I had to manufacture my own material for the installation.  I talked through options with my technical counselor an we decided on an approach that maintained the existing rivet holes and took advantage of  gaps in the rivet flanges of the rib. I started by fixing the location of the VOR base on the rib, and then slowly ground back the rib flanges until each of the antennas were clear of interference.  This was followed by drilling a hole in one of the flanges for the hex key used to lock the antenna in place.  After verifying correct positioning, I then transferred the hole locations onto the skin and slowly and carefully cut out an hole for the antenna to pass through the skin, starting with 2 pilot holes and finishing up with files to obtain the final desired shape.

Next in line will be finishing the horizontal stabilizer and putting together the skeleton of the elevator.

All in all it has been a productive couple weeks and I am happy with the progress.

Horizontal stabilizer skeleton riveted
Test fitting the rudder and horizontal stabilizer

Riveting the rudder - for this rivet, since there was not room to directly use a rivet gun, I used a aluminum
 wedge with a rivet with a bent mandrel to give me the required clearance - worked perfectly!
Finished horizontal stabilizer
Rudder skins riveted on both sides
Vertical Stabilizer skin with hole for antenna element

With antenna element installed - the additional small skin hole between the clecos is for the
hex key to tighten the element in place.
Test fitting both elements of the VOR antenna 

Sunday, September 21, 2014

First Month Complete!

The first month of building has come to a close, and after spending the first few weeks of doing preparatory work, I have finally started to set some rivets.

I started construction with the horizontal stabilizer (HS).  It was very straight-forward to put together and no issues came up as it was riveted.  I have only riveted one side of the skins because I have a tech counselor who will be visiting in the next week to review my work to date - after his inspection I'll close out the other side of the skins.

After completing one side of the HS, I moved on to the rudder.  Similarly, no particular issues arose building the rudder skeleton and riveting one side of the skins. As with the HS, I've leave the other side of the skins non-riveted until the tech counselor drops by.

Next on the list will be the vertical stabilizer (VS)  - stay tuned for an update on that, including mounting a VOR antenna.

See below for some photos of progress over the last couple weeks.

Horizontal stabilizer clecoed and
rivets positioned, ready to be set

The very first rivet set!
Horizontal stabilizer skeleton complete
One side of horizontal stabilizer skin riveted
Rudder skeleton riveted - note the counterweight
One side of rudder skin riveted

Sunday, September 7, 2014

First Couple Weeks

It has now been a couple weeks since I received the empennage (tail) kit.  I have managed to find some time to work almost every day  - sometimes it is only half-an-hour, but the plan is to work on it every day to some extent to keep the progress going.

I've had to split time between working on the build and finalizing the layout of my workspace. I still have a few things to set up in the garage, but going forward the majority of time will be spent on the build instead of the shop.

To help familiarize myself with the empennage construction, I test fit all the individual pieces (elevator, vertical stabilizer, horizontal stabilizer, and rudder), using clecos instead of rivets to hold everything together.  Going through the test fitting helped me sort through how the pieces will eventually all fit together, and will help me plan the sequence of riveting when that is started.  All the components fit together very well, which is a great start.  There are also a couple pieces that need to be match-drilled to ensure a proper final fit, so I also took care of that during the test fit.

After the test fit, I broke down all the components and started the process of deburring and cleaning all the structural components and the skins.  As of today, all the empennage pieces are deburred and cleaned, and the framework for the rudder, horizontal stabilizer, and the horizontal stabilizer has been primed and is ready for riveting.  I did have a minor set-back when I ruined a couple pieces as I was shifting things around in the garage - fortunately it was before I had done much work on them so I won't lose any time, but it will take a while for the replacement parts to make their way to me.  Also had one piece that had a crack in it that the factory will be replacing for me.

So, all-in-all,  it was a productive first couple weeks and I am thoroughly enjoying the process!

Here are a couple of photos from the last couple weeks:

Doing inventory - these are all rudder components
Test fitting the elevator trim tab
Test fit of elevator  with skins
Test fitting the horizontal stabilizer
Match-drilling the horizontal stabilizer
Test-fitting the vertical stabilizer
Horizontal stabilizer cleaned,tagged and ready for degreasing
Horizontal stabilizer degreased and ready for priming
Horizontal stabilizer primed and ready for riveting
Rudder (left) and vertical stabilizer (right) components
primed and ready for riveting

Tools and Jargon

To help understand the various steps involved in the build, I thought it would be helpful to spend some time discussing the activities and the tools we use to perform them. I'll add to this list as the build progresses and new techniques are learned and applied.

Firstly - let's introduce the general airplane construction since that defines the techniques and tools that will be used.  The majority of the skeleton and surfaces on the Sling 4 will be aluminum; a few fiberglass pieces complete the picture.

The primary method of joining aluminum pieces together is riveting. In the Sling 4, the majority (and perhaps all) of the rivets are called pull rivets (also called blind or pop rivets).  You have probably seen this style of rivet on many items around your house, and the ones I'll be using are similar in function, but of a higher quality and strength. Installation of a pull rivet starts by placing the rivet tail into a hole that is common to the pieces of aluminum you want to join. Using a pneumatic or hand riveter, the mandrel is pulled back, which compresses the tail and locks the pieces of aluminum together between the head and tail of the rivet. The mandrel snaps off on its own,leaving behind the final rivet holding the work together.  There will be thousands and thousands of the rivets in the Sling 4.

Examples of various sizes of pull rivets to be used in the Sling 4 empennage

Here are a couple of the tools I'll be using to set the rivets
Hand (left) and pneumatic (right) riveters

However, there are several steps than one needs to complete prior to riveting to prepare the pieces to be joined and to ensure longevity of the components.  The majority of parts in the Sling 4 kit are pre-shaped and pre-drilled so that little modification is required to enable the pieces to fit together properly.  However, there will be a few pieces that need to be drilled in spot to ensure an accurate fit, and every piece needs to be deburred and prepped.  Deburring is the process of removing any burs or sharp edges to reduce the potential for metal fatigue and cracking. Every piece in the kit needs to be inspected and deburred to at least some degree.  In addition, there are sharp edges and corners on every piece that need to be rounded.  There are a wide range of tools used for deburring - some are hand tools:

Hand deburring tools

.....and some are electric:
Scotch-Brite Deburring Wheels (these are not stone grinding wheels)

Finally, many individuals choose to prime the pieces to reduce the long-term potential for corrosion.  There are many different primers and ways to apply them, but I have chosen to work with an epoxy primer that is sprayed on.  To prepare for priming, the aluminum be cleaned, degreased, and abraded to provide an optimal surface for the primer to adhere to - a lengthy process but it will be much more durable.

Here is an example of a primed piece of aluminum (bottom).
That green color will be a tell-tale sign of what I have and haven't primed

Here is an example of a couple pieces of aluminum being riveted together.  First step is to cleco the pieces together to hold them in the final desired position.  A rivet is then inserted into one of the match-drilled holes. A riveter is used to pull the mandrel of the rivet, which compresses the tail and sets the rivet.  As the riveter continues to pull the rivet, the mandrel snaps off and the rivet is complete.

Rivet ready for setting
Rivet head set

Thursday, August 21, 2014


This blog will serve to update friends and family on my build of a Sling 4 airplane.  The Sling 4 kit is provided by The Airplane Factory through its US Distributor.

After many years of enjoying flying my Cessna Cardinal, I decided that I would proceed down the experimental path.  Many reasons played into this decision, among which were education and recreation, lowering operating costs, and acquiring modern avionics at a reasonable cost.

Although most of my flying has been by myself, I wanted the option to seat up to 4 adults.  I didn't have experience working with either aluminum or composites, but I felt that going the sheet-metal pathway would be best for me.  To that end, I signed up for an EAA metal workshop to try my hand before making the final decision to pursue that path.

There are currently only a few 4-seat experimental metal kit options.  I had seriously looked at the Vans RV-10, but that is a lot more airplane than I currently fly and the build time was rather daunting.  I came across some information on the Sling 4 and decided it was a nice compromise.  Yes, I would prefer something that had a little more top end speed, but the reality is that the Sling 4 will cover all my planned uses.  I still have not actually seen a Sling 4 in person, but have test flown the Sling 2 at the US factory office and thoroughly enjoyed the handling and visibility.   While there certainly will be some differences between the Sling variants, I am sure that the Sling 4 will be every much as enjoyable.

The blog will follow the build process by the major airframe components/activities:
  • Empennage, including horizontal and vertical stabilizers, elevator and rudder;
  • Wings, including fuel cells, flaps, and ailerons;
  • Fuselage, including canopy, doors and landing gear;
  • Firewall forward, including engine, propeller and associated electrical and fuel components;
  • Interior, including seats, panel and avionics;
  • Final finish (painting or perhaps even wrapping)
I won't update this every day, but will try to post at least once a week to keep all informed of the latest progress.  

Whatever your reason for dropping by, I hope you enjoy the blog.


UPDATE: The empennage kit arrived on Friday, Aug 22, 2014, meaning the build has officially started!

The Airplane Factory Sling 4 (Photo from TAF SA website)