OK, I'm calling this the official start of build prep (debatably, that started with my balsa bending experiments, but whatever).
Because the first thing I'm actually going to do is fabricate the helical fins, the first bit of prep I need to do is create the template for them. This was an interesting little exercise. My template needs assist with three tasks:
1) cutting the balsa
2) positioning the balsa on the bending form
3) position the finished fins on the pylons for final assemply
Although it's not really the right tool for the job, I created the template with Paint.net. Here's a half-sized annotated version:
The footprints for the two pylons came first. Positions on the X-axis are easy: they come from OR. Positions on the Y-axis are slightly more interesting. The helical fins conform to a 5" cylindrical form, and the front and back are exactly 60 degrees apart. Therefore, the distance along the circumference of the cylinder is 1/6 the total, or 5*PI/6 = 2.62". And so that is the height on the Y axis of the front pylon on the flat paper.
Then, via all sorts of fiddling, I created a symmetrical tapered fin shape that covers the pylons, and looks about the way I want, as shown above. That will serve as a template for cutting the balsa.
I also put vertical rules left and right, to line up with the edges (or at least one edge) of the cylindrical form I'll use to bend the balsa. I'll wrap the paper onto the form, trace the fin outline onto the form, and then that will help me position the balsa correctly on the form.
Finally, after the pieces are finished, the pylon markings will help me mount the helical pieces onto the pylons in the correct position.
So everything is accounted for I think. We'll see!
Because the first thing I'm actually going to do is fabricate the helical fins, the first bit of prep I need to do is create the template for them. This was an interesting little exercise. My template needs assist with three tasks:
1) cutting the balsa
2) positioning the balsa on the bending form
3) position the finished fins on the pylons for final assemply
Although it's not really the right tool for the job, I created the template with Paint.net. Here's a half-sized annotated version:
The footprints for the two pylons came first. Positions on the X-axis are easy: they come from OR. Positions on the Y-axis are slightly more interesting. The helical fins conform to a 5" cylindrical form, and the front and back are exactly 60 degrees apart. Therefore, the distance along the circumference of the cylinder is 1/6 the total, or 5*PI/6 = 2.62". And so that is the height on the Y axis of the front pylon on the flat paper.
Then, via all sorts of fiddling, I created a symmetrical tapered fin shape that covers the pylons, and looks about the way I want, as shown above. That will serve as a template for cutting the balsa.
I also put vertical rules left and right, to line up with the edges (or at least one edge) of the cylindrical form I'll use to bend the balsa. I'll wrap the paper onto the form, trace the fin outline onto the form, and then that will help me position the balsa correctly on the form.
Finally, after the pieces are finished, the pylon markings will help me mount the helical pieces onto the pylons in the correct position.
So everything is accounted for I think. We'll see!
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