EMPENNAGE FIBERGLASS

 

On February 13, 2003, I began the tedious (understatement) of installing the fiberglass tips on the tail plane.  Manufacturing parts from fiberglass does not save time, money or aggravation.  The only advantage is the ability to make pieces with smooth curves or tight radii that is difficult to do with aluminum.  The stabilizer, rudder and elevator tips are examples.  I started on the right elevator.  The only significance to starting on the right elevator is that it was still on the work bench from its assembly.

 

Gap between tip and counterweight Aluminum back-up strips

 

The Photo at the left above should look familiar.  It also appears in the RH Elevator assembly log (I cropped it so I could enlarge it).  When the elevator was completed, I started the tip installation before I took any pictures.  The tip installation looks like it should be straight forward but nothing is ever as it seems.  Note the open front around the weight.  Also note the large gap between the tip and the weight.  After seeing the gap I decided to call it a day.  On February 14, while I pondered what to do about the gap, I busied myself with the trim and fit of the tip.  I also decided to make some aluminum strips to back up the fiberglass for rivet installation.  See photo above right.  No material has less strength at fastener holes, in both shear and tensile, than fiberglass.  I installed some AN426AD3-3 rivets to hold the strips in place for final assembly.

 

Picture of the gap on the left elevator tip

Counterweight with “Marine Tex” in glass cloth

 

The photo above left shows the gap on the left elevator.  It is a better picture of the problem than the one of the right tip above.  I decided that not only should the gap between the counterweight and the tip be filled in but the lead counterweight should be covered up as well.  Lead is very soft and surely will get beat up as time goes by.  Also, I am not sure if paint will stick to very well.  I decided some form of fiberglass re-enforcement was in order.  I have, on many occasions, used an epoxy putty called “Marine Tex” in conjunction with fiberglass cloth to make repairs to fiberglass parts.  It is possible to do some forming without the need for a mold using the following procedure.  The procedure is basically very simple.  Step one is to apply masking tape to any area that you do not want to have fiberglass resin/epoxy putty on.  Then the “Marine Tex” is mixed per the instructions.  (I found out a few years ago when I was in a big hurry that if you over catalyze epoxy, it will NEVER set up!)  Apply this mixed up paste to the part.  Put a layer of fiberglass cloth over the putty and work it into the putty (photo above right).  The cloth needs to be wetted out with the putty just like regular resin.  The advantage to this is that the putty will stay put and hold the cloth.  The cloth is there to strengthen the part after it is cured.  Once the cloth is properly wetted out the excess along the aft side of the counterweight was trimmed off with a pair of scissors (I forgot to take a picture of the trimming).

 

Tip cleco’d in place. Note sealant and second coat of putty Clamp installed during cure time

 

While the putty was still wet, I installed the tip over it.  There is about 20 to 30 minutes of working time with this stuff, so there is no hurry.  I even took the time to install the tip wet with sealant (PR890B 1/2) between the tip and the end rib of the elevator.  When the tip was cleco’d on, I put another layer of “marine Tex” over the counter weight.  This was done to finish filling in the gap. I attached the tip with CR3214-4-2 “Cherry Max” rivets.  See the picture above left.  Now before you get all excited about me installing the tips wet with sealer I will explain why I did it.  We found a box of fuel tank sealer in our facility in Gallatin that someone left behind.  It was outdated but I wanted to se if it was useable.  It was useable but I never used any more of it.  I also never installed any more fiberglass wet with sealer.  After the rivets were all installed, I   installed a clamp on the end of the tip to hold its shape while the putty dried.  See above right.  The next day I sanded the tip.  More filling is required.  That has not been done yet.  I will fill and finish all of the tips at the same time.

 

Left elevator counterweight Close-up of counterweight after shaping

 

This entire process was repeated on the left elevator tip.  I did not take duplicate photos since at times I had sealer or epoxy putty on my hands and my digital camera is very expensive.  In fact most of the previous photos are actually of the left tip because as I was working on the right tip I was developing the tip installation plan and photos were not always on my mind.  One thing that I did not touch on in the narrative above is that the counterweight needs to be filed substantially along the front and the sides.  This is to make room for the thickness of the fiberglass.  The photos above show the left counterweight after it was “sculpted.”

 

Elevator and stabilizer assembly Stabilizer requires trim at elevator cut-out

 

The photo above left shows both elevators completed and temporarily attached to the horizontal stabilizer.  It also shows the stabilizer tips in place but they are not done yet.  This picture was taken after I made a new holding fixture for the stabilizer/elevator assembly.  The photo at the right shows that some trimming of the stabilizer skin was required before the stabilizer tip could be installed. 

 

Trimming the stabilizer skin. The stab tip trim line aft side of the tape

 

Trimming was easy enough.  I marked the trim line with masking tape.  Then I drilled a ¼” hole for the radius at the corner where the two cuts converge.  Next I trimmed along the tape line with a pneumatic “mini” grinder.  This task was accomplished on both upper and lower skins.  I then put the elevator back on and laid out trim lines for the tip.  I removed the elevator and transferred the trim lines to the tip.  I trimmed the tip.  I took these same steps for the tip on the opposite end of the stabilizer.  All of the “easy” work was now done on the horizontal stabilizer tips.

 

Aluminum “mold” in RH stabilizer tip Aluminum “mold” taped in place with aluminum tape

 

The horizontal stabilizer tips come with the aft end open.  The assembly instructions suggest some methods to close out the tips but I preferred to go another route.  I have some aluminum sheet metal other than that which came with the kit.  It has protective coating on both sides.  The Marine Tex epoxy putty will not stick to the protective coating so the metal is good for making simple impromptu molds.  The photo on the left above shows one of the stabilizer tips with a piece of plastic coated aluminum wedged in to the area that needs to be closed out.  The aluminum had to be cut to shape before installing.  The other tip in the photo is still open ended.  The aluminum piece is curved slightly to match the curved front of the elevator “horn.”  The right photo shows the aluminum “mold” taped in place with aluminum tape.

 

Fiberglass cloth cut to shape Waiting for epoxy to cure

 

After the aluminum “mold” was cut, formed and taped into place, two pieces of fiberglass cloth were cut (left photo).  The smaller of the two went on first.  The procedure was the same as the one used on the elevator tips.  Epoxy putty is mixed, spread on the inside and cloth is wetted into putty. The only difference is that two layers of cloth were used.  They went in separately.

 

A completed stabilizer tip A stabilizer tip installed

 

The photo on the left shows the tip after the aluminum “mold” was removed and the closeout was trimmed.  The photo on the right shows a tip installed on the stabilizer.  This is the other tip.  By comparing the two photos, it looks as though the tip in the right photo is a little wider.  It is wider.  The tips are a little narrower than the elevator horn and I did not notice this until I had finished the closeout on one of them.  I have to cut this closeout out of the rib and make another one.  The “mold needs to be wider before glassing in the closeout

 

Rudder and vertical stab. With tips Rudder lower cap after trimming

 

The rudder and vertical stabilizer are next.  The left photo shows rudder and stabilizer temporarily assembled and the three tips are next to them on the work bench.  I started on the rudder lower cap first (RH photo above).   I am on the road to having it fitted OK here, but I am not satisfied with the way it looks yet.  Also, I think that this cap needs to be removable.

 

Another view of rudder cap Rudder and vertical stabilizer tips.

 

While I contemplated what to do with the lower cap on the rudder, I decided to install the upper tip on the rudder and vertical stabilizer.  The right photo shows the two tips installed.  The rudder tip required a lot of trimming, even more cussing and even a little temper control before I got it to fit.  I don’t know why it was such a chore but it was.  People who build all fiberglass (or “composite,” which I believe is the current technical term) because they think it is easier don’t realize how wrong they are.  The extra energy expended is not always worth it.  The photo above right shows the rudder top cap and verticabilizer top cap i

 

Gaps taped over and filled with Marine Tex Epoxy resin and cloth over the Marine Tex

I decided to fill in the area I previously trimmed on the rudder lower cap.  At this point I was sorry that I was so hasty in trimming it in the first place.  I put tap over the cut-outs on both sides of the cap and put Marine Tex over the tape.  I then put a layer of cloth impregnated with epoxy resin over the Marine Tex.  Here is a handy piece of information for you.  Epoxy resins as a rule stick well to fiberglass parts made with polyester resins such as these tips.  Polyester resins as a rule do not adhere well to parts mad2e with epoxy resins.  If you are wondering why I didn't just wet out cloth with Marine Tex for these gaps it is because I wanted to keep the area the same basic thickness as the tip.  Also I was no forming around square corners as before and epoxy resin is easier to use to wet out the cloth.

Tape and ink cut lines Trial fit of the two sections

 

The next step was to cut the tip into two sections.  The photo above left shows the cut lines.  I cut along the tape around the bottom of the cap.  I then cut along the ink lines.  At right are the two sections in place on the rudder for a trial fit.

 

Fiberglass cloth and epoxy resin inside cap Two sections held together with aluminum tape

Next I put a liberal amount of mold release wax on the rear section of the cap on the inside.  The tape on the inside is where I stopped with the mold release wax.   I taped the two sections together on the outside with aluminum tape and put two layers of cloth on the inside of the cap.  I then mixed some epoxy resin and wetted out the fiberglass cloth.

Two sections separated Flange after trimming

 

After curing overnight I separated the two sections (above left).  I then trimmed the excess and voila; I have flange to install screws into to hold the two sections together.

 

Marking cap for drilling holes Cap cleco'd in place

Now I needed to drill attach holes in the fiberglass where the cap will be attached to the rudder.  I also drilled three attach holes from the rear section into my "new" flange (above right).