Sunday, July 16, 2017

Painting Roundels and Center Section Installed

 The grand kids, Rowan and Duncan, visited for a couple weeks around Independence day.  We had a nice dry day near the end of June so we started painting the roundels on the lower wings.  We made a cardboard pattern and drew the circle with pencil on the wings.  As with the rest of the SPAD paint scheme the roundels were brushed on.  One thing we learned was, unlike dope, Poly-Tone really softens the the paint you're applying it to.  It will take at least 2 coats of white to get the cream not to show.  They had fun and we made progress.

The weather has been mostly hot and humid.  Today wasn't to bad so I installed the center section.  We fit the center section to each wing before installing it just to make sure I put all the fittings back on correctly.  Everything fits nicely.  Once the cowl is permanently installed I can safety wire the turnbuckles.  Nice to be putting things back together.

Sunday, June 4, 2017

Dad's Pitts Special Model 1951 - 2017

While visiting my parents for my Mom's 90th birthday party I noticed my Dad's old Pitt's Special model.  Going with Dad to the flying circle was one of my favorite treats.  Watching him fly that Red and White Pitt's is just one of those great memories.  The plane has always hung in his workshop a never fails to remind me of going to the flying circle and watching him and all his friends flying, dog fights, jets and stunt jobs.  It was great fun!  I think is was a major reason all I ever wanted to do was build and work on airplanes.  We built a Fly Baby and fixed op an L-2 Taylorcraft while I was in High School.  Fifty plus years later as an A and P, Private Pilot, and Aerospace Engineer, I still have the Fly Baby, and 2 other projects.

We were looking for something in his shop in the barn and I asked him when he built the Pitt's, since it just always seemed to be a part of our lives.  He couldn't remember exactly but he always took pictures of models he built and has the pictures all in albums, many albums.
We got to searching and sure enough there was a picture of my older brother David (right) holding the plane in 1951.  Dad's in the middle and uncle Peter, 2 years older than David on the left.
We did some more searching through all Dad's well organized magazines and found an add for the Pitt's on the last page of the January 1951 issue of Model Airplane News.  The add for the McCoy 29 was on the back cover.  The kit was $4.95 but the engine was $11.95.  Dad, a retired cop, always worked part time at a hobby shop so I suspect he at least got a small discount.
The model appears to be one of the few which never crashed.  I think the real hobby is fixing busted planes.  All the paint job on the wings and tail is done with the original decals.  I never realized it was all decals until we got looking at it.  He was thinking he should recover it.  I suspect there aren't many models that old and still so original.  The only change has been to rotate the engine to the outside.  I wondered if it ran better that way or if it's a different McCoy than originally installed.  Engines moved from model to model and had a way of occasionally getting damaged in the dirt, usually at high speed.  Ah the excitement of watching airplane parts flying in all directions, when it's someone else's plane.  The truth is much simpler, the control lines didn't stay tight with the engine facing into the circle.  Turning the engine to the outside solved the problem.

We decided to recreate a couple of the pictures of the Pitt's.  The spiffy shirt is long gone but their current house has  the same shingles as the old one.  The tissue paper is starting to fail but other than the pilot, added some years later, it's all original, and in very good condition.

The day we took these pictures dad was getting ready to start working an a large scale P-40 kit he got in a deal for his P-51 model which the other fellow should enjoy flying as much as dad did.  The P-40 has retracts and all so it should keep him busy for a few days.

I'm glad he still has the Pitt's.  The memories it brings back are treasures.

Brace Cable Length Fixture

Having figured out how to make the wire wrapped cable ends the way I wanted, I needed a way to make sure the cable length was correct.  Wrapping and soldering the ends was too much work to remake one because I messed up the cable length.  When we assembled the plane the first time we did it in the barn, and just made each cable to fit the plane with the wings held in position.  When I started this it was fall and I didn't want to leave the plane assembled in the driveway for weeks.  I also wanted to recover the wings while I made new cables.

To control the length I made a simple fixture from 2x4s and some pieces of angle iron.  The block and angle bracket on one end is screwed to the 2x4.  The other end can be positioned to the desired length of the cable and just clamped to the 2x4 frame.

I assembled the plane and rigged all the cables tight.
I measured each cable length from the edge of the fitting, at one end,to the center of the pin, on the far end of the turnbuckle, at the the other end.

The fixture is set up to duplicate cables using the distance between these same references, the edge of the fitting and the pin at the far end of the turnbuckle.

I made a bracket at the fixed end to hold the fitting.  It's screwed to a piece of 2x4 which is screwed to the 2x4 base.
I found I needed to protect the fitting paint from scratching so I made a protector from a plastic blister pack.  It had a nice fitting square corner.

The 3 holes are for socket head cap screws which keep the fitting from sliding off the end of the bracket, which it did without them.
My length measurement starts from the fitting side of the bracket.  If I had been thinking, I would have positioned the angle bracket on the block so the fitting side of the angle was in line with the edge of the block
I took all my measurements in centimeters because it was easier.

The movable block was made so the measurement between the edge of it and the edge of the fixed block is exactly the length of the cable.  As a result all I have to do was measure from the fixed block, draw a line for the front of the movable block and clamp the movable block on that line.

The bracket on the movable block has eye bolts for the turnbuckle pins.  Since all my wing brace cables are double I used 2 eye bolts.  In the end I did each cable as a separate piece so I could have done this with 1 eye bolt.

One advantage I found to 2 turnbuckles was the ability to easily lock the turnbuckle barrel so it wouldn't unscrew while working.

I crimped the Nicopress sleeve on the free end of the cable but did not wire wrap it until cutting the cable to length.  You can't spin the cable while it's still attached to the reel of cable.

With the length set and the turnbuckle at zero threads showing, I pulled the cable snug, then cut it off about 8" past the fitting end bracket.

The turnbuckle end was then wire wrapped and soldered.

I found a couple nails and a safety pin made simple stops to keep the cable end from turning in the barrel.

Slip the Nicopress sleeve on the cable, pull the free end of the cable around the thimble on the wing fitting, then back through sleeve.
To grip the free end of the cable, so I could pull it tight, I modified a cheap pair of Vise Grip type pliers.  I used a chain saw file to make a groove to fit the 1/8" cable.  I felt it gripped better than flattening the cable end in the jaws.  The groove needs to be such that there is a slight gap when the jaws are tight.

This works really well.

I removed the adjustment screw on the pliers and installed a 5/16" eye bolt so I could use a ratchet strap to pull the cable tight.  The cheap pliers had a metric bolt with threads very close to 5/16 UNC.  I just ran a tap down the threads to clean them enough for the eye bolt to turn freely.

The ratchet strap works well to pull the cable tight.  To keep the 2x4 from bending I screwed another 2x4 to the bottom, forming a "T" section.

I also added some 2x4 feet so I can clamp it to saw horses at a convenient working height.

With the cable tight the Nicopress Sleeve is positioned with a 1/16" gap to the thimble, as on the other end, and squeezed.  I had to take the cable out of the fixture to make the squeeze closest to the fitting.  If you don't you just can't see what you are doing to position jaws.

My original idea was to leave the first cable in position while crimping the second cable.  With very little thinking I would have realized the 2 cables were too close together to squeeze the second cable with the first one tight.

Tip it back out of the way and do the second cable.  You still need 2 slots in this bracket for everything to fit.

The cable is then ready to finish wire wrapping the ends as discussed in the previous posting.

Friday, May 19, 2017

Brace Cable Terminal Ends

The Nicopress tool instruction sheet shows the cable eye end made with about 1/16" of cable sticking out of the sleeve.  I figured out how to do it and we'll get into it later.  As discussed earlier, my objective was to make these nice old thyme looking cable ends with a Nicopress sleeve and the cable end wire wrapped and soldered.
There are 2 ways to form the cable end.  One is to use an AN 100 Thimble.  The other is to use AN 111 Bushing.  The bushing works fine where it is able to fit into the fork end of a turnbuckle.  The Thimble works fine in a fitting or the eye end of a turnbuckle.  The only time a Bushing is a better choice is under high loads.  Under high loads the Thimble tends to flatten which causes the cable to lengthen which alters the rigged geometry of the plane.  This does not happen with a bushing.
We used bushings, on the turnbuckle ends, for most of the rigging cables on the wings.  They fit the turnbuckles we used, Army surplus.  The problem I ran into was keeping the bushing at the end of the cable while forming the loop.  Just bending the cable around the bushing doesn't form the correct radius so it tends to leave a gap at the end between the cable bend and the bushing.  You can pull it tight on installation, but it affected trying to get the cable the correct length.

To solve this I decided to Pre-Form the bends on the cable end.  They did this on old, WWI, brace wires made from piano wire.

I made a bending jig with some angle iron and dry cell battery terminal nuts.  They are just the right radius and they have a groove which perfectly fit the cable.  Being made of brass they do not scratch the cable.

There is one nut screwed to the base angle.  I drilled out the threads on the one at the pivot for the bender.  The pivot bolt is threaded into the base angle.  Then there is one nut screwed to the pivot arm.  I used nuts with 10-32 threads.

To form the eye we will make 3 bends, one around each nut.

I start with the pivot to the left and about 4"- 5" of cable sticking out past the first nut.

The line scribed on the base is the finished bend line for the first bend.

Hold the cable in position.  With a block of wood, held tight to the first nut, bend the cable so it springs back to the bend line.

With the first bend positioned on the first nut and the cable end on the bend line, swing the arm all the way until it stops.  This makes the second bend.

My first attempt at the third bend was to just pull the end of the cable back to form the bend.  This makes a loose and poorly positioned bend.

What worked better was to hold the top of the cable, bend 2, tight to the top of the second nut.

Then use the block of wood to form the bend around the third nut just like the first bend.

Much better.  The 2 cable ends form about a 90 degree angle between each other.

Now the sleeve and bushing can be assembled for crimping of the sleeve.  I found the bushing didn't stay tight in the bend until the sleeve was crimped.  You can hold it in position with the cable clamp or my pair of fluting pliers worked great.  Just don't adjust them so tight you crimp the cable.
You just want to hold the cable snug to the bushing.

I clamped the pliers in the vise to hold everything while crimping the sleeve.

On 1/8" and larger cable always start with the center crimp then crimp the 2 ends.

It makes a nice strong cable terminal.
When using the Nicopress sleeve with a thimble, AC 43-13 recommends trimming off the pointy ends of the thimble.  This allows the sleeve to fit closer to the bends at the end of the thimble.  I trim off about 1/2 the pointy ends with the belt sander.
The cable end is held in the cable clamp and the sleeve positioned to leave about 1/16" of a gap from the thimble.  You might say then why trim off the thimble?  When all the crimps are made the gap will be gone because crimping makes the sleeve longer.

Crimp the middle then each ends.

To form the cable end like the Nicopress instructions showed, I started with a shorter free end.

Position everything in the cable clamp and mark the cut about 3/16" past the un-crimped sleeve.

Protect the cable with 20 gauge steel and cut off the end of the cable.

Re-position the sleeve and crimp it.

The finished terminal leaves just a tiny bit of cable sticking out, as shown on the instructions.  Instead of making the cut square, if the cut had been made at about a 15 degree angle, long ends closest to the main cable, there would be even less chance of getting snagged on the free end.

Back to our wire wrapped look.  The cable end is in our cable clamp with the sleeve crimped.

The piece of PVC pipe provides a support for the cable while rotating.  Otherwise it just flaps and you can't rotate it while wrapping the end.

CAM-18 recommends soldering the cable before cutting of the free end to length.  I found it just as easy to cut before soldering.  I don't think they had Dremel Tools back then.  You still need to protect the cable.  I used a short piece of steel for a guard but CAM-18 recommends a piece 3" long so you don't accidentally damage the cable.

You need a cut at about the angle of the twist in the cable so the wrap wire won't slide down the slope while wrapping the end.

I found it much easier to wrap if I pre-soldered the cable, where it will be wrapped.  Then I clamped the cable and the free end tight together with a cloths pin and c-clamp.

This allowed me to heat the cable, with my soldering iron, and sweat them together.  You need to let it set for several minutes to cool enough to remove the clamp.

Sweating them together holds them tight for wrapping and make the area stiffer for wrapping.

The wrap starts at the sleeve as shown in the earlier posting. and progresses to cover the free end completely plus about 1/4".  The one thing I've learned since then is, it's easier to wrap rotating the cable so the top of the wrap is moving away from you.  You can see the wire better as it's being placed so you can keep the winds tighter.
When soldering I found it worked better to start at the small, cable only, end and work toward the sleeve.  Rotate the cable to be sure you've completely soldered all the way around the wrapping wire before moving along the joint.  It's easier than trying to warm up an area to solder a spot that got missed.
When it's done you have a nice looking cable. All the wire should be soldered and the solder should fill the gap between the cables.

The cable ends with a turnbuckle were easy to wrap using the cable clamp to hold it while wrapping.  The ends at the wing fitting required a slightly different method.  The fittings are too big to fit in the clamp.  I thought about designing a different cable clamp but found I could do them just fine without it.  If I were doing the full wire wrap method I would need a different clamp to hold the cable tight while wrapping, but the Nicopress sleeves were installed in the fixture I built for controlling the length of the cable.  The sleeve securely forms the loop end so all I needed was a way to hold the cable while wrapping the free end of the cable

The wing wires are all double wires.  To rotate the cable while wrapping I just used 2 pieces of PVC pipe to hold the cables.

With a way to hold the cable the rest of the process is not much different.  I cut the free end to length, tinned the cable with solder, and sweated the cables together as before.
I used the wing fitting as a kind of lever to hold while rotating the cable.  Again, rotating the top of the wind away so I can see the wind develop.

The tube made a nice rest to hold the wound cable while soldering.

I found it convenient to wrap both cables a the fitting and then solder them.

I think I'm ready to make the tail surface brace cables for My WACO NINE project.