Monday, 2 May 2011

Starting with the easy parts

I spent the Spring, and Summer of 2010 collecting the raw materials required, spar grade Sitka Spruce, mahogany aircraft plywood, 4130 steel tubing, as well as various hardware, and components.

By late July I had the materials ready to begin the lower wings, as well as the required tools, incuding a new table saw, planer, sanders, bandsaw, drill press, router, and bench grinder all on hand.
I had also built the benches and tool stands.

By August I had run out of excuses.

I started the lower wing ribs August 25, 2010, and made good progress for a week, until I realised I was building them completely incorrectly.

Great, so that was a waste of a week, 2 sheets of really expensive plywood, multiple now useless fixtures and lots of spruce. 

Nice start.

I then worked out the correct rib construction method by re-studying photos of the EAA replica ribs, but it was an expensive lesson to thoroughly study every detail before cutting wood. 
EAA lower wing ribs, also showing a solid spruce
compression rib
New correct lower wing ribs
Then I realised just how hard the actual ribs were to build! I can only assume that E.M. Matty Laird had lots of very dedicated and inexpensive employees making what are the most time intensive ribs I have ever seen.
Each rib requires an inner spine of 1/16th mahogany plywood, which is routed in a three step process. Each process requires a separate router fixture. Pre-shaped upper and lower spruce capstrip, both also slotted to take the plywood spine, each inner spruce capstrip must be pre cut to length and angles, then notched to slot over the plywood spine, and all is then assembled in two special assembly fixtures.
No nails are used in the rib construction, only epoxy, and I reached a point where I could build 2 ribs per day, one to the finished assembled point, and one to the first fixture point. There are 28 ribs in the lower wings, some truss, some compression, and some with different spar slot widths.
Slotted spruce capstrip 
Fixture to pre-bend capstrip leading edges
The lower wing ribs were completed by October 2010, they were quite a steep learning curve, as they taught me the value of checking details again and again befiore commiting to the parts.
I realised I was not building another Pitts, and this would be a very different experience to my previous building projects.

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