Taylorcraft CF-CLR: Tail Feathers

June 2016
Was back in February I sprayed the Polybrush and Polyspray coats and began to have problems with contamination..

The initial problem was traced to the tack cloths I was using. I usually just use the yellow ones from the local paint store, but I thought I'd "treat" myself to some "Boeing approved" versions. Anyway back to the cheaper yellow ones....

I carefully prepared the tailfeathers and a few small parts for top-coat. The paint went on ok and looked good.

The next day I couldn't believe what I was looking at. No trace of the tack cloth problem but still far too many specs and in localized areas, craters/fisheye or whatever you want to call it when the paint flows away from a tiny pin-head size circle.

I immediately assumed it was my equipment ie bad air, bad filters, bad hoses etc. So set about fixing all of that. No problems found but I went through it all anyway. I called Polyfiber and they were very helpful. The suspect... not waiting long enough between prep wiping with C2210 and applying topcoat. Further discussions with people in the know suggested using an alcohol based cleaner was the way to go.

I've also washed my paint "booth" from top to bottom, sealed off every potential leak, and installed new finer filter elements. By the time all of this was done I was well past the 72-hour timeline for re-coating and the tailfeathers needed to be wet sanded anyway to remove the blemishes. I've yet to get back to painting as I've been concentrating on fabricating parts....

Christmas 2015
Finishing tapes were applied to the tail feathers and fuselage concurrently. Its good to have a couple of things on the go rather than waiting for glue to dry. It basically kept me from being too eager with the iron (which works better if the Poly Brush is dry).

So having several well lit work benches/spaces is nice to have.

I took the time to make a couple of 2" straightedges out of some odd pieces of plexiglass I had. Makes short work of marking out rib tapes.

I thought about removing the nav light mounts during the frame repairs and frankly I wish I had cuz it's a pain forming fabric around that shape!

Anyway the rudder trailing edge was done in three pieces.

This at least enabled avoiding the use of bias tape as much as possible. Bias tape pinks unravel easily.

From the nav light up I used straight-cut tape and

heat formed the curve.

The leading edge is two tapes, one below the control horns and one above.

A method of getting a good butt joint is to trace the tape below with the soft pencil.

Usually enough of a shadow can be picked up to provide a guide for the pinking shears.

The stabalizer rib tapes are butted. Seemed like a reasonable way to do it.

Trailing edge tape goes on first on the stab (after the rib tapes of course).

I tried to heat form a straight tape but couldn't make it work, so I used bias for the tip and straight for the remainder.

Straight and bias tapes are butt joined at the rib tape.

a little heat forming is needed at the inboard curve,

and it lays nicely.

Corners are finished with butt joints.

With both stabs done except for drain grommets I turned my attention to the elevators.

Access to the trim mechanism is needed along with the opening for the pushrod.

2 inspection rings are installed though I'll only open one.

The pushrod opening is the same as the rudder cable openings on the fuselage.

Four grommets are installed on top in the locations marked before the bottom fabric was applied.

These will aid in trim servicing if the belcrank needs to be removed for any reason, but will be left closed unless needed.

The Poly Fiber manual says to work fast to pull bias tapes in one shot. For me anyway it's just about impossible to ensure the tape remains on the centreline and/or the edge lines. The Poly Brush drys either too fast or too slow depending on what you're trying to do, and when you so much as breath in the general direction of the pinked edges of the bias tapes, they begin to unravel.

So, in place of applying Poly Brush first and then fighting time and the tape, I attached the inboard end, once dry I pull the tape into position, taking my time and lining it up perfectly with the right amount of tension to achieve the correct width. Clamps are used to hold the tape in position and snug against the tube.

Once happy, I attached the center-line 1/4" or so by soaking it with Poly Brush from the outside. Once that's dry the clamps are removed and the remaining 90% of the tape is attached in the normal way by carefully lifting the egde of the tape, applying Poly Brush to the underlying fabric, and laying the tape into the Poly.

The right elevator trailing edge is done in one piece in the same fashion and a good result is achieved with the bias tape.

Poly Fiber stresses laying tapes into wet Poly Brush, but also says, in regard to rib tapes, that as long as the outer portions of the tapes are well attached your good. So I applied the same reasoning to the bias tape (and the centre of the tape is well stuck anyway) for a much better way of applying bias tapes imo.

With all the doilies, tapes and gussets installed, drain grommets are added and yet more time is spent with the iron, smoothing out lumps and bumps and making sure things are stuck.

Tail feathers are ready for spraying.

October 2015
The tail surfaces seem to be a good place to start the covering adventure and fresh from attending the Polyfibre workshop at Oshkosh I felt primed and ready.

I won't regurgitate the Polyfibre manual, rather I'll point out some things that I found work and some details that are not in the manual.

At the OSH workshop we covered a mock stabilizer which had no hinges or other obstacles that make things a little more complicated.

Remember to apply the anti-chafe tape cuz it's no fun having to un-glue the fabric (only made this mistake once so far!)

Cut the fabric with lots of extra (only made this mistake once so far too)

Fold the panel in half and crease. This provides a good starting point and makes it easy to mark and cut the hinge locations.

The manual talks about using a razor blade to trim the excess fabric. I prefer to form the fabric first, mark all my cuts with a pencil, paint them with fabric adhesive,

and cut with scissors before gluing the fabric in place. The result looks better, I think it's actually faster, and more importantly, no chance of damaging the primer.

Forming the curved edges is about trying to shrink the fabric in one direction only, so there needs to be enough extra to keep good tension on the fabric as the iron is applied.

In one place the manual says you don't need to glue the leading edge when the fabric is one piece top and bottom. Then in the next paragraph it says to glue. Anyway at OSH we glued. This allows the bottom fabric to be shrunk at 250. Then to get the required overlap a pencil line is drawn. The top fabric is then heat formed as required and the pencil line is visible through the fabric. Excess is then trimmed and the fabric is glued. The edge of the top fabric is glued to the pencil line (even if it causes wrinkles along the edge...which are removed later with the iron). This procedure renders a nice straight edge.

There is minimal room for the trim bellcrank in the elevator, Mine was installed with AN3 bolts with 75% of the heads shaved off. This time it's installed using clevis pins which have a much lower profile and the same hardness specification as AN3 bolts.

Before covering and with the tab and push rod installed, I measured were the rod will emerge from the fabric.

Once the fabric is shrunk to the final 350 degrees, I transfer and mark the coordinates.

On the top surface I mark locations for grommets that will be installed but not opened (until bellcrank removal is required).

The rudder must be covered in two pieces because of the control horns

The stabilizer flying wire attach points are opened with a soldering iron after shrinking the fabric to 350.

The smell and need for fast but smooth brush strokes bought back memories of my first ever airplane covering project... a Sterling Ringmaster, a glo-engine powered control line model airplane my father and I built when I was perhaps 5 or 6 years old

We live in a "sound-bite" world where TV shows complete home and auto restorations in 60 minutes or less. So to put a little reality behind this project, the photo above represent over 5 full days to cover and Polybrush 7 parts. And this is the easy part!

Next up is rib lacing

after a few attempts at deciphering the Polyfibre manual, I went to Youtube and found a number of useful videos on tying the modified seine knot including one which is also on the Polyfibre site.

Keep on lacing....

March 2015
One thing that can be done in the cold is welding. I expect, when the weather finally warms up, I'll be glad I did most of the welding tasks in February.

First up was the left stabilizer. It was serviceable, but at some point someone had done an external sleeve repair on the leading edge. Clearly visible it was something that always bothered me so a new leading edge tube was the order of the day(s)

Now the leading edge is 7/8" chromoly and it really really wants to stay straight! I concluded that even if I could find a tube bender for this size tubing locally, it would probably be of the type that "allows" some deformation. So.... I set about building one. There was a good deal of trial and error but my only regret is that I didn't video the machine in action, it worked so well!

The leading edge is bent to the exact shape of existing before dismantling

Both ends are left long until final fitting

The existing stab is blocked up on a flat work top. Unfortunately I don't have a steel table, but at least it's easy to attach blocks.

Also use a sharpie to trace the outline of all parts. A simple way to double check that things go back together right

The leading edge is cut off

Leaving all the rib material and some of the old tube.

Each weld is carefully trimmed back, leaving the part as it was before it was originally assembled

Tip is cut and gradually trimmed for a good fit

Ready for tacking

After tacking, the fuselage is needed to check fit

Several checks to make sure things are straight. Here fishing line is strung from tip to tip to help make sure I get the stab attach bolt holes in the right place.

Next up, both elevators needed work

The left elevator had apparently been tweeked so I copied the tip bow shape from the right elevator which looked undamaged. Anyway this will ensure both elevators are the same shape.

Right elevator is laid out in the same manner for replacement of the leading edge and most of the trailing edge

The inboard end of each elevator has a .050" sleeve. 1" O/D tube is cut along its length and the fishmouth such that once clamped to the leading edge there is a 1/8" gap.

The sleeve is welded together and to the base tube at the same time.

Ready for tacking.

Note that the elevator trailing edge doesn't lay flat on the table. The shorter the chord the closer the centreline of the trialing edge is to to the c/l of the leading edge. The drill bits taped to the table are lifting the trailing edge the calculated amount.

The objective is to get things as close as possible on the table. After things cool down, final adjustments are made by cold forming.

I was a fair welder once. Welding takes a steady hand, good eyes, and patience. Apparently as I become impatient, my vision deteriorates and my hand gets shakier! The good news is a weld doesn't have to look pretty to be strong!

Anyway, I'm particularly good at contaminating the tungsten electrode with welding rod. This resulted in frequent trips across the shop to the bench grinder. I finally smartened up and put tips on all my electrodes (duh) at once, a six fold increase in efficiency!

Of course replacing the leading edges means replacing the hinges. First I need spacers to get the stab-elevator clearance correct

Thick wall chromoly tubing supported by steel of the right thickness to get the hinge on the centreline. A small tack is applied. Any larger and the cooling weld has a tendency to pull the hinge out of position

Flip the elevator over, check the hinge for straightness (easily eyeballed because I have the 2' of tube still attached), tack this side, then flip over again and weld the top side, then back again for this side.

the excess tube is cut off, but not the section iin the middle (where the male hinge on the stab fits)

I welded a drill bit to a steel rod to open the hinge to the final dimension

Finally the elevator is fitted to the stab

Repeat for left elevator, paying extra attention to the trim system structure

Right elevator bellcrank was only lightly tacked on the bench and final position checked once the tailplane was rigged.

CF-CLR has a tailplane for the first time in about 28 years

While things were together, I also temporarily installed the trim system and identified several items needing attention

The trim horn had been repaired with a doubler, and drilled to -4 and it was worn beyond that

So a new horn was made. I used 050 chromoly in place of the 040 mild steel (added the lightening holes so it's about the same weight!) so hopefully it will wear a little better.

The clevis on the pushrod was also replaced

Closer look at all the possible lost motion points reveals the screw-jack shaft end-play as a significant contributor.

I found a nylon washer that was the perfect thickness to eliminate the free play.

The crank handle rollpin hole is relocated 90 degrees and the Tcraft gets treated to a couple of DC-8 thrust reverser bushings so, for a while at least, the trim crank handle won't have the usual floppy feel.

One of the spot welds had popped on the tab and a small crack occurred at that location. One 3/32 rivet was added and PRC was used for additional bonding.

I formed an eye on the end of the hinge pin with the idea that it will be both stronger for the cotter pin retention method and easier to remove.