Tuesday, April 28, 2020

Heavy Compression Rib


Earlier I ground down the end of the Heavy Compression Rib to fit over the interplane strut fitting.  The factory just made the rib short by the thickness of the of the steel and used a piece of 3/32 plywood to fill the gap beyond the fitting.  I may do that on the last 2 wings.  The factory kept changing what they did after all.











Case in point, the wing assembly drawing shows 2 screws holding that compression rib in position.  One screw directly into the spar and the other through a hole in the strut fitting.

The old spars only have one screw and the other end was nailed in place, no second screw.  Go figure.




It turns out the forward end of the rib on the lower wing is the only place the screw in the hole and the second screw actually go in straight.  All the other positions require one of the screws to go in at about a 45 degree angle.  It may be that they drilled the hole in the fittings in different locations on each wing.  We need to go back and check all the fittings.  I've located the holes based on the fittings I had at the time.  Even then some of the screws need to go at an angle.
To get the screw to align with the hole I marked the holes on the end of the ribs, then used a #40 drill back to the corner where the screw head will set.  Then I re-drilled the hole with a #10 drill.


The screw sets nicely in the corner.

You can see the one hole in the corner and the other located where it's properly square to the wood.
I went back to the #40 drill, from inside the rib, through the hole in the fitting.

I stuck a drill bit in the hole so you can see it worked out well.

The Upper wing forward and aft screws both go at an angle through the fitting, and straight into the wood above the fittings.

The lower aft end goes straight though the hole but at an angle to clear the edge of the fitting.

When the wires are tight it's hard to imagine these moving even without the screws.


Monday, April 27, 2020

Wing Rib Gusset Problem & Wing Walk Outboard Rib Wire Holes


 For the wing ribs on the follow-on Model TEN, the WACO factory added a gusset to the center of the long middle bay on the ribs.  As long as the bay was I'm sure they had the cap strips bend or even break.  The gusset really stiffens it up.

Unfortunately the gusset interferes with some of the drag wires on the Model NINE.  Had I thought about it I would have re-positioned some of the gussets to assure they cleared the wires.  Oh Well.

 At this point all I could do was file some notches in the gussets to clear the wires.  I used a 1/4" chain saw file.  Eventually I got bored and switched to the small sanding drum on the Dremel tool.
 The notches on some of the gussets were so deep I added another piece of gusset .

This is the outboard bay.

 The center bay


 The inboard bay.


 The drawing for the outboard wing walk rib showed hole locations for the drag wires.  I wasn't convinced they were right so I waited until I was ready to install it to saw the holes.  I'm glad I waited.  They were way off.  They were probably the the locations for the model TEN.

The rib fits nice.


Wing Trammel Points and Starrett Trammel Points


 To square up the wings we adjust the length of the diagonal Drag and Anti-Drag wires.  The turnbuckles are used to both tighten the wires and to adjust their length.

The idea is that if you adjust the wires at each bay so they are the same length the wing will be square.  You can't easily measure the length of the wires.  Instead we mark points on the bottom of the spars and measure between them to square up the wing.
 We don't actually take a measurement with a tape measure, but you could I suppose.  Instead we use some Points, like on an awl, attached a small beam.  Mine were made by Starrett.  They clamp onto a stick, in this case spruce.  The one is fixed, you clamp it where you want it.  The other has a thumb screw which adjusts to position of the point to increase or decrease the distance between the tips of the points.

To measure the diagonal distance between the points marked on the spars at each bay, you set the fixed point at one mark, then adjust the movable point to align with the mark on the other spar.  Then you use this length to measure the opposite diagonal length and adjust the turnbuckles to lengthen or short the wires.  As you adjust the length of the wires, and re-tighten them, you needed to readjust this length between the trammel points until the 2 wires are exactly the same.

 I used the optical center punch to make a light punch mark at each trammel point, on the bottom of the spars.  The punch mark makes it so much easier to do this by your self.  Now that that I've worked out the locations for the points I'll mark the spars for the other wings before I start assembling them.

On the lower wing the points are located at these distances from the root end of each spar.
Root 2"
Light Compression Rib 46 13/16"
Heavy Compression Rib - Inner Bay 91 3/4"
Heavy Compression Rib - Outer Bay 93 1/4"
Tip Compression Rib  139 5/8"



 On the Upper Wing the points are located at these distances from the root end of each spar.
Root 2 1/4"
Light Compression Rib 55 9/16"
Heavy Compression Rib - Inner Bay 108 11/16"
Heavy Compression Rib - Outer Bay 110 3/4"
Tip Compression Rib  156 5/8"

Now I can start adding part to the wings.



Thursday, April 23, 2020

Finishing the Ferrule Installation Tn The Wires

The wires are formed, and the fittings and turnbuckles are in the loops.  Now I need to slide the ferrules tight to the loop and bend the tab over.  Unfortunately the ferrules fit very tight, even if the 2 pieces of wire are very straight.  I experimented with several clever ideas for how to seat the ferrule, well maybe not so clever.  I finally figured out a simple process for all this which seems to work well.
First off the wires are about 5 feet long and bend easily so I needed a stand tall enough to keep the end of the wire off the floor.  Hanging vertical seems the only safe position.

All this resulted in a stand I can clamp to my work bench.  The long piece of 2x4 has a slot sawn in it for the wire to dangle in, while pounding the wire down into the ferrule.

The base board allows it to be clamped to the workbench and the angled pieces, nailed in place, make it all rigid.


The end of the 2x4 is too soft to last long pounding on it so I added a piece of 1/8" x 1 1/2" steel angle.  I still have 84 ferrules to do in the fuselage when the wings are done.  The slot makes it easy to set the wire and ferrule in it.  The vertical leg of the angle traps the ferrule with the wire in the slot.

The ferrule is trapped on a solid surface and the free end does not touch the floor.

Before putting the clips and turnbuckles on the wire ends all the Loops were painted.  I did them now so the clips and turnbuckles don't shadow the wire and so I'm only painting the wire.  I'll paint the ferrules and main part of the wires after finishing the ferrules.

The ends with the wire clips cause a little problem.  There is no way to pound directly on the end of the loop because the clip is in the way.  I suppose I could pound on the clip, too tacky.

I made a pounding block from a piece of 1" square oak with a notch to fit over the clip and wide enough to just clear the eyelet.


You just pound it down until the ferrule is firmly seated against the loop.

With the turnbuckle end you just use a plastic mallet and pound directly on the loop.  So easy.

The next thing is to bend the free end around the ferrule to lock it in place, without bending or nicking the main wire. 

I clamp it in the vise tipped like this so it won't rotate up when I bend the free end.

I start with my modified Vise Grip pliers about 1/16" from the end and start the bend up just enough to move the pliers in closer.  I want the bend tight to the ferrule.

With the pliers re-positioned I bend the end up to about 90 degrees, as far as I can until the pliers touch the ferrule.

Reposition the pliers, rotated 180 degrees, then bend to the ferrule.

To close the bend a little further I squeeze it in the vise.

It leaves a fairly tight bend which will give 85% to 90% of the strength of the wire.  I use the loop shaped like an AN100 thimble to minimize the stress at the bends.  A more round shaped loop will break at an even lower load.


The WACO Factory used tinned wire and soldered the ferrule after making the locking bend.  I can't get tinned wire, which has Hydrogen Embittlement problems that can cause the wire to fail.  To tin the wire you have to use very aggressive flux containing hyrdo-whichever acid.  The hydrogen gets trapped under the tinning, eventually penetrating the steel matrix preventing it from flexing.  It shatters instead.

NACA Report No. 3 says that soldering adds no strength to the joint.  They recommend wrapping the free end with wire to lock it in place, adding a little more strength to the joint.

To do this I clamp my modified pliers in the vice and use them to hold the ferrule and keep the free end tight while wrapping with safety wire.


I use 3 turns with 0.041" stainless safety wire.  Twist it tight.  Fold the cut end under for safety.  I am so tired of bleeding on everything.  Then release it from the pliers.  It looks like the picture in Report No. 3 only I use 3 turns they used 1. 

The safety wire sets nicely in the grooves of the ferrule.


 Solder may not add strength but it seals the ferrule joint and protects it from rusting.  I wanted to create the same protection for all my hard work.

I was planning to fill them with epoxy but it is too viscus and will not flow into the voids without a vacuum to pull it in, much to much work.  Instead I seal the outward end with a dab of 5 minute epoxy.  I'm creating a little cup with the epoxy making the bottom and the coils of the ferrule making the sides.

I like to control the mix of small quantities of epoxy with 2 equal size circles for a visual guide.


 I'm using a bamboo skewer to mix and apply the epoxy.  The point is nice for applying and you just cut off the used end and resharpen it for each new batch.

I let this seal, on each ferrule, cure for 5 minutes hanging on a peg seal end up.


After the seal cures I fill a small syringe with Oil based spar-polyurethane varnish to seal the inside of the ferrule and wires.  I think I found these for giving babies small amounts of medicine.  They say monojet on the side and hold 1.0 ml.

I slowly drip in 0.3 ml of varnish.  Then I hang them to dry for a day.  I wrap the clip or turnbuckle with foil in case a little drips out.


When the varnish dries you can see it has just penetrated between each of the coils.  Everything inside should out last me and the grandkids anyway.


The ferrules and wire get a coat of primer and 2 coats of metallic Rust-Oleum Satin Nickle.

Yea!!  We can finally build a wing.