My Hatband replica build

[Jmk89]

Today saw the start of actual building of my attempt to replicate John O'Donnell's Hatband Coupe model  (for the earlier attempts to find information and discussion on how certain design features were determined, see this thread).

I started by setting out the wing outline.


As the picture shows, the tip is a laminated outline (1/4" x 1/32" x 3 laminations).  The leading edge is 3/16"sq balsa shaped by clipping the front top corner down to about 1/16" above the building board.  The LE in the tips is soft, that in the centre panels is medium.  The TE is 1/8"x 3/8" balsa shaped using my tilted sanding block to give a 1/32"rear edge - again the density of the balsa differs, with medium in the tips and medium hard in the centre panels.


I also have produced the straight wing ribs:

This photo shows the sandwich with the blanks glued together using glue stick and the templates attached to the blanks using double-sided tape.


Here is the "block" after shaping using razor plane, rasps and sanding blocks.  The eagle-eyed may notice that three of these are 1/16" thick and the rest are 1/32" - the 1/16"ribs go at the dihedral breaks.  Also some of the ribs are darker than the others - they are medium hard balsa for the centre section panels and the lighter coloured ones are medium soft for the tip panels.


And then into a butter tub containing isopropyl alcohol.  They should have separated by morning, and then can be laid out on newspaper to dry.

Tonight is the National Rugby League grand final and, although it is not usually something I take much interest in, one of the teams competing is the Newcastle Knights.  I spent two years in Newcastle as a kid which I enjoyed greatly so I have a soft spot for the city and would like the Knights to win.  So I may shape the diagonal wing ribs while listening to the radio broadcast.

[Jmk89]

The Knights lost 19-18!!!

But the ribs came out of the alcohol in good condition this morning and are now drying on some workshop hand towel.

First the straight ribs


And now the diagonals

[MEETOO]

Looks like you made great progress today. Will follow the build  with interest.

[Jmk89]

Thanks MEETOO.

I was lucky and got some more time today (public holiday in NSW), so I made some good progress on the wing.

First, once the wing ribs had dried out, I glued in the 1/32" straight ribs - the 1/16"straight ribs will be glued in when the dihedral is being set. 


After  the glue had dried, I started fitting the diagonal ribs.  Although it looks like you fit them with lap joints and each rib being straight, I crack each one so one diagonal rib occupies one rib bay.  To measure where the crack needs to go, I hold the diagonal rib with its front end in the intersection between the LE and the rib on the other side of the wing bay and the rib going back along the diagonal.  Where the diagonal rib intersects the straight rib I mark the diagonal rib - that's where the rib has to be cracked.  If you are going to err here, err on the side of making the nose section a smidgeon longer, but don't get carried away (this is why you make wing ribs a good 3mm longer than the actual length ).

Next, bend the diagonal rib so you can check that the front part follows the correct line from the LE intersection with the "other"  to the mid-point of the current rib.
To make the crack, I position my scalpel blade on the rib where I want the crack and lift one end until I feel the rib weaken.  Then stop.  You don't want to break the rib in half, just make it bend.

To make the crack, I position my scalpel blade on the rib where I want the crack and lift one end until I feel the rib weaken.  Then stop.  You don't want to break the rib in half, just make it bend.


 

[Jmk89]

Part 2

The next step is fitting the bent rib.  The photos show that in the tip bay which is a bit extreme, but you will get the idea.


Sand off any excess from the nose of the diagonal rib so it a good fit in the front part of the wing bay. 


Then sand the tail of the diagonal rib until it fits neatly.  Then glue in place.

When gluing, put a smear of glue on both sides of the rib at the mid-point crack.  That way the outside of the bend will stick to the straight rib and the valley of the crack will be re-inforced by a glue bead. Be very stingy with the glue for the valley. 


And here's where I left off.  The next step will be setting the 3 dihedral joints.

[OZPAF]

That's a neat trick with the diagonal ribs Jeremy.

I must admit that I might have used a trammel sanding approach to shape the straight and diagonal ribs from blanks in situ. it's very quick and produces accurate ribs.

That's fast progress.

John

[Jmk89]

Thanks for your comment, John.

I considered using the trammel method, but with 1/32"ribs and some big gaps between them, I thought I would go with the method I'm more comfortable with.  Whenever I've tried the trammel method, it has proved to be unlucky for me.

I think that this is a bit like the woodworking debates about how to cut dovetails.  Everyone has their preferred method.  They all work and really it's just a question of personal preference which one an individual likes to use. 

Today I did the tip dihedral and inserted the straight ribs at the tip dihedral break and the diagonals in the bays next to those ribs.

First, make (3D print) a sanding block with an 82° bevel to put an 8° slope on the LE and TE of centre and tip panels at the dihedral break. Pin down the centre panels and prop up the tip panels by 2". Sand the 8° bevel on all 8 LE and TE surfaces.


Glue the LE and TE and put in the ply reinforcing braces. Pin the tips in place and leave to dry.


Once dry, and with the panels still pinned in place, use the 82° blocks to prop the dihedral break straight ribs and glue them in place and let dry.

[Jmk89]

Part 2

Once dry insert and glue diagonal rib in bay of centre panels next to dihedral break straight ribs.  I do that step now because the centre panel is sitting nicely on the building board - doing diagonal ribs "in the air" is the sort of step I am bound to stuff up.  Leave to dry.

Finally, unpin the two wing halves and pin tips to the building board and prop up the centre panels.  Fit and glue the diagonal ribs in the tip bays beside the straight rib at the dihedral break.


Next step - join centre panels at 3° dihedral.

[THB]

Neat work Jeremy - following with interest
Tim

[Jmk89]

Today, I joined the wing centre panels, added the centre straight rib and the diagonals on each side and then started inserting the wing spar.

First, joining the centre panels.  With each panel propped up 5/8" and the panels pinned down at the centre, the LE and TE were glued to each other and the ply braces were glued in place.  Left to dry.




Then, the 1/16" straight centre rib was glued in place and left to dry.


Once dry, one centre panel was pinned down flat on the building board and the diagonal rib next to the centre rib on that side fitted and glued in place.


Once that side was dry, the process was repeated on the other centre panel.

[Jmk89]

Part 2

Inserting the wing spar.

I decided to follow the spar concept of Teachers Pet - hard 1/16"x 1/8" balsa in the centre panels with  a doubler spar for about 2/3 of the span and ply braces front and rear of the spar at the centre rib position; and medium hard 1/16"x1/8" balsa in the tips and a ply brace between the tip spar and the centre spar at the dihedral break rib.

Here are the full length centre panel spars glued in place with the front ply brace in position.


Of course, the spar notches never line up exactly, so each needs to be adjusted with a fine file.  I put pins each side of the ribs to try to stop them moving around as the file does its work.


After a spar is fitted, it is glued and weighted in place until the glue dries.