Freebird ornithopter

Nederlandse tekst

I wanted to build an Ornithopter for a long time, but it's complexity held me from it. But finally I printed the Freebird plan and started building. It is supposed to be 16" span but on A4 it printed out at about 90% of this size. It builds really easy compared to the scale stuff I usually build. In two evenings it was finished!

The model has already flown. In my living room it makes a nice full circle at almost constant height. I tried this on a few office rubber bands and I still have to make a proper rubber motor. The video is from the website.

The hardest part is bending the crank. On the plan a simple alternative is given, which needs only two 90 degree bends. But the more complex crank gives a nice symmetrical flapping action. Here is how I did it:
- I started with the SFA prop-hook,
- then I put the hook in the bearing and put 2 beads on the wire,
- made a 90 degrees bend,
- made the second 90 degree bend,
- put on the first (basswood) connecting rod,
- made the other 2 bends and put on the second connecting rod,
- put on a bead and glued on a small tube.
- I put the connecting rods between beads on the wing lever wire, and again secured by a small tube

To make the bends I use a small plier with a very thin jaw. It wasn't as hard as I expected and it took me only a few minutes.

What I found is that the wing bearing position didn't match the crank position. Partly because of the beads I used, but also because of the space needed for making the bends. I would advice to make the crank arrangement first and glue the wing bearing in the right position so it lines up nicely.
Covering is unshrunk an unfinished Esaki tissue.

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I tested it on a parking place between some large buildings. At first it didn't do much on its loop of 2.8 g/m rubber. It did a level flight, not more. I switched to a long 3.1 g/m (1/8") loop, but this was no improvement. So I bent the tail a bit up, switched back to the original motor and put in as much turns as sensible and tried again. This flight gave me a fright! It took of as a scared bird and started circling to the blue sky. It went over a barb wire fence, over a building, over a few large trees, passed a few big fences again and I was running behind her. When she started to descent it was above a big fenced area
But luckily it just cleared one of the fences and landed on the road next to it. That flight must have been close to 3 minutes! This bird really flies!

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laatst gewijzigd op 08-nov-2012