Haven't done much in the shop on my own stuff lately, as I've been helping Ron with his Aeronca Scout rebuild and puttering away on the 701 wing rebuild. I'm gaining confidence in my ability to fabricate simple aluminum channels and web caps and learning the value of measure twice, cut once, fit and debur before riveting. Pictures to come!
I've also been talking at length with Ron and he's all but convinced me that building my 750 from "scratch" (hand make all the parts from raw aluminum stock) rather than via prefabricated kit components from Zenair is not only doable, but really economical. It's what he's done with his 701 and has shown me how easy the process actually is. The monetary savings to be had by forming the parts myself is nothing to scoff at either, perhaps saving upwards of 75% on what Zenair produced parts cost! Sure, there are some things it makes more sense to buy direct (windshield comes to mind), but the more I think about it, the more I like the idea of scratch building (and it means more learning!)
So what does scratch building entail? Basically it means making forms out of wood from the plans which in turn will be used to form the raw sheet aluminum into ribs, channels and other associated parts. Other flat parts (wing skins, fuselage panels) are measured and cut directly from aluminum sheet stock.
The obvious trade off is time, but Ron and I both believe the goal of 3 years building is easily achieved.
In order to determine how much aluminum sheet to order (the Zenair plans unfortunately don't include a comprehensive material list), I'm working on converting the appropriate plan drawings to scale CAD files. In the spirit of money savings, I've found an excellent free online CAD program called LibreCAD that makes converting the dimensional drawings in the plans to CAD files easy.
For example, I can take the drawing of the Horizontal Stabilizer Nose Rib from the plans:
.....and use LibreCAD to turn the information from the drawing to a CAD file, suitable for printing, exporting to a CNC machine, etc:
As you can see from the screenshot above, I'm not including the dimensions on the CAD drawing, as they are just as easily referenced on the paper copy. I've also created the CAD file with 3 different layers; form, aluminum and a label layer. Each of these can be toggled on or off for easy viewing should the need arise.
I am however keeping an Excel spreadsheet to document each drawing that has been converted. Once I have the drawings all converted, I'll be able to place parts of the same material thickness onto a page representing a complete sheet of raw aluminum. This should save material and money as I can nest smaller parts (ribs, channels, etc) among the larger ones, saving material waste.
The spreadsheet also tracks what forms I've got made and what parts are completed and ready for assembly.
I never had CAD available to me as a highschool drafting student, but that part of my brain that knows how to interpret drawings still works it seems! Is this worth the effort? Who knows. I'm just enjoying the journey!
Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.