Fabric on!

If you plan on building an airplane, plan on doing a lot of research.  Fabric covering an aircraft is a complex process and will take a great deal of research to figure out, as I can confirm after this past week.  Fortunately, there are great resources out there such as walkthrough videos on the covering process and manuals that detail every possible step.  Finally felling ready, albeit apprehensive, the fabric hit the rudder today.

The first step was to prepare the ribs for rivets.  To attach fabric to a control surface, you need to attach it at regular intervals with one of three generally used methods: stitching, rivets, or screws.  After consulting with several builders and learning the kit suppliers recommendations, I decided to go with the same 1/8" stainless steel rivets that I am using on the aircraft structure at 4" intervals along each rib.  If you choose rivets, then the first step to covering is drilling, deburring, and cleaning the holes for the rivets.  Two things learned here: (1) order a bulk pack of the drill bit you use most, in my case the #30 bit for the 1/8" rivets, because drill bits break and it really is frustrating to have to stop work because you don't have a spare bit; and (2) a good deburring tool (like this one I picked up from Aircraft Tool Supply) will really make the work quicker and cleaner.

 

Now, with the rivet holes in place, I went over the rudder with 220 sandpaper again to make sure I didn't have and areas that would tear the fabric.  After running a clean rag over all the surfaces and making sure there were no snags, it was time for tape.

 

 

I used cloth tape from Aircraft Spruce to cover all the rivets and metal edges in what turned out to be a more tedious process than expected.  The kit manufacturer says you can get cloth medical tape from a drug store which seems like it would work better as it feels like it has more tack to the glue.  This tape required a lot of pressure and time to bond to the frame. 

 

 

I tried diligently to keep the tape free of wrinkles and finally used an awl to punch holes in the tape at the rivet holes in the ribs.

 

Another thing I wish I would have done differently: the screws holding the bottom of the frame and the middle rib to the spar should probably have been countersunk a bit more.  They protrude out slightly and if they were a bit more flush the project would look cleaner.

 

 

Next, I took the 2.7 oz Dacron Fabric and traced out the rudder with about a 6" overlap.  On the second side, it worked a lot cleaner when I trimmed and clamped the fabric over the spar and then traced out the 1" overlap as suggested by the Stewart System videos.  However, for this first try I'm glad I left some extra fabric to trim as I needed to correct a cutting error.

 

To cut the fabric, I used another cool tool, the Florian Pinker.  It cuts a pinked diamond-shaped edge on the fabric continuously as it rolls along.  The pinked edge is supposed to prevent the fabric from fraying and supposedly ads to the adhesion strength when glued.

 

 

Up next, applying the glue, EkoBond, to the rudder.  That the teal colored stuff on the picture. Per the instructions, I applied a full layer of glue around all contact edges and let dry.  It only took about 15 minutes to dry to a tacky surface that was ready for fabric.

 

 

Starting the process of hand tacking the fabric to the glue was another difficult task as I was constantly adjusting the fabric and trying to keep it straight and lined up.  With this glue, you can get a nice temporary tack by just using hand pressure, and can simply pull it off and re-tack it with a little pressure if you need to as you go.  That helps to hold things in place until you apply the head to get a firmer tack, and allows for error correction.

 

 

Working very slowly, I used my small hobby iron at 230 degrees to tack fabric to the frame, taking care to try and be as smooth as possible on the rounded edges.  When it was all done, while the heat did take out most of the wrinkles, there were a few left.  Hopefully the final shrinks of the fabric and the final heat process will clear those up.  By far, the most difficult portion was the corners where you have to trim and fold them just right. 

 

After the whole frame was tacked, I passed the iron around the tubes on the inside to seal the fabric overlap.  Honestly, I was greatly relieved to see things look cleaner at this point. I was worried that it wouldn't bond or look right until now.  But, seeing the fabric start to adhere smoothly gave some confidence.  I was still worried though, as the fabric was quite loose.  I thought I have maybe left too much slack in the fabric and would have to redo it all.

 

 

I took the iron over the fabric at 230 degrees for the first shrink and wow!  it tightened up and started to look like a real control surface! I was impressed this far. After that, I trimmed out the second panel of fabric, this time using clamps to hold it at the base of the spar while I measured for the 1" overlap.  This time there was no room for excess trimming, so that saved time.

 

 

This panel took only a few minutes to get right, much quicker than the first one.  It is always a good feeling to get better and faster at a task.

Another layer of EkoBond glue around the fabric covered frame, this time carefully wiping away the excess with a shop towel and working hard to keep a clean and even line for the next panel to adhere to.

 

Same thing on the other side, and we are ready for panel #2.

 

 

 

Second panel is on, again carefully working to keep wrinkles out of the curved edge.  This time, I was not as successful at that task.  Hopefully the finishing tape will hide those imperfections.  A pass with the iron for the first shrink and it looks pretty good though!

 

 

Remember those rivet holes?  Over the top of the ribs I applied a strip of 1/2" reinforcing tape, then punched a hole with the awl at the rivet holes.  I then took the drill, set on a very slow speed with a #31 bit, one size smaller than the hole, and ran it through the hole to allow the rivets to be pushed in.  The rivets took a little force, but the slid into place and were easily pulled solid with the air rivet gun.

So far so good!  It looks like a rudder!

At this point, I've been at it for about 4 hours, so it was time for one last task before I called it a day.  I find that I start to rush things and quality suffers after about 4 hours straight, so I'm trying to prevent that.  The last project of the day was a reinforcing patch over the slit in the fabric for the control horn.  I cut out a 10" x 5" rectangle with the pinking shears, then a pinked cut in the middle for the horn to pass through.

I glued the patch area of the fabric, let it dry, then heat-sealed the patch in place.  Hopefully this patch will make the fabric strong and durable here so no tears will form at the control horn cut.

That's it for today!  Next is the finishing tape, then on to primer and painting.

Practice Build Time:  4.5 hours

Rudder Ready for Covering

Today started, per usual, with me learning that I probably should have done things in a different order.  I took the freshly machined control horn and started scoring the holes on the rudder spar and rib for the control horn bolts, but soon realized that securing the nut underneath the gusset already riveted in was going to be difficult.  Next time, I'll have to wait to rivet in the gusset until after the control horn.  This will allow clean access to the nut and will allow me to line up the rivets on the gusset so they don't interfere with the bolt, two of the problems I had today. 

 

After scoring for the holes, another problem emerged:  My drill was too large to give me a straight angle to drill into the rudder rib. So, off to Harbor Freight again where I picked up this pneumatic angle drill.  I intended on getting the electric one, but they were out of stock and the shop is set up for air, so for $27 after coupon this one did the trick. 

 

 

The bolt holes were drilled out with a #11 bit and I really liked the air drill, it allowed for good bracing so the holes were clean and on point.  After a quick deburring the AN3-10A bolts were slid in place.  For the nut end under the gusset, I rigged up a thin wall 3/8" socket to a long extension bar so I cold hold it firm while ratcheting the other end.  That did the trick, but I didn't like the stress it placed on the gussets to get it in place.

 



 

After the control horn was bolted in, I started fabricating two angle braces that are not in the plans, but suggested to me by master builder Sam Buchanan who used them on his Fokker project.  I started off by cutting out two pieces, each 2" by 4", from the gusset thickness aluminum sheet, then bent a 90 degree bend with the metal brake right down the middle long ways.  Then, the pieces were traced out over the control horn to fit, sanded, smoothed and deburred, before the next step.

 

 

Two rivet holes were drilled using a #30 bit in the control horn and braces for each side, and one rivet hole for each side was drilled where the brace connects to the rudder spar.  After the deburring and locking in with Clecos, they looked smooth and strong, ready for rivets.

 

 

Once the stainless steel rivets were pulled, I was happy with the result.  The control horn fells strong and stable enough so that it can take the forces of taxi and braking.

 

 

 

With the practice rudder fully fabricated, it is next time to try my hand at covering.  I have to watch the covering video from Stewart Systems again and will be back at it soon.

 

Practice Build Time = 2.5 hours

Machining the Control Horn

It's been 5 months since the last post, but I've been spending that time researching building and covering techniques and reading up on other builder's projects.  I've shown my rudder to some A&P (one of which is my father) and have come to the conclusion that I can actually build this thing.

There is a mindset that goes into this process that I don't think I had at the beginning.  I guess I expected a little more detailed instructions, but this is an airplane, not a bookshelf from IKEA.  The extra time I have had to take to learn construction and fabrication techniques is well worth it, as when this is all done I will not only have built the aircraft but also have the tools and the knowledge to fabricate replacement parts and fix any issues.

That said, I am moving on with the practice rudder to make sure I understand the process.  My plan is to finish it through covering and paint.  If that goes OK, then I know I can do this.  The next step in the rudder is to fabricate a control horn, and the 6061 aluminum sheet for that is too thick to cut with snips, so I purchased a new tool, this Harbor Freight Band Saw beauty:

Where have you been all my life?  I wish I had this at the beginning of the build, it trims through aluminum like butter leaving a clean, smooth, and straight cut that requires very little deburring or sanding.  If you are building an Airdrome Aeroplanes kit and don't have one of these, you need to get one.  It will make life ten times easier.

After tracing out a control horn copy on the 6061 sheet, I cut it out with the band saw, used the drill press to put in the pilot holes, then ran it through the sander to get all the edges smooth and the corners round without any burrs.  It took about an hour, but the end result is as good as the one from the kit.  The horn from the kit is the one on the right and mine is the one on the left:

 I ordered some AN bolds and nuts from Aircraft Spruce, got 20 each of bolts and nuts for about $5 so that I will have extras in the parts bin if I need them. Before doing that I took a quick internet lesson on decoding AN bolts and found a nice chart that I printed and laminated for the shop.  Next, I'll be bolting the control horn and hinges on.

 

Once that is done, I'll test my ability at covering the rudder.  I orders a sample kit from Stewart Systems for $100, and it should be enough to cover the rudder, plus it came with a box of DVDs on how to apply their covering.

 

 

 

Planning/ Research time = 1 hour