Flying challenge

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Adam and lift test

4. Flapping mechanism
The crank wire is the most difficult part of the ornithopter, but you've had practice. Also, if you make a mistake, you can easily cut off the crank wire and make a new one.

Bend the motor hook first. Then slide the wire through the bearing tube on the bottom of the fuselage. Cut a 1/8" long piece of aluminium tubing as a thrust washer and slide this onto the front end of the wire. In Figure 1 (the first diagram in the image below), you are now ready to bend the crank itself.

Make the first bend by grasping the wire with pliers just ahead of the thrust washer. All bends are 90°. Carefully make the second bend so that it is in the same plane as the first, so that in Figure 2 of the image below the wire is parallel to the bearing tube.

The third bend rises directly "out of the page" (Figure 3), and the fourth and final bend leaves the wire once again parallel to the bearing tube (Figure 4).

Make two connecting rods (conrods) from plywood. The critical dimension is the distance between holes, which are made by piercing the wood with a straight pin and enlarging the hole with cut wire. Slide these onto the crank.

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5. Wings and Tail
Make a perpendicular hole through the tail and fit the tail onto the rear spur. Make sure the tail is not crooked, then glue and bind with thread.

Insert wing lever wires through the wing hinge tubes. Bend the wires as close as possible to the hinge tubes to hold the wings on, bending in the same plane as the wing lever. Cut off excess wire. Wings should swing freely and should be perpendicular to the fuselage.

Now apply the tissue covering to the tail. First apply a thin coat of white glue (dilute with 3 parts water for best results) to the upper surface of the frame. Then apply the model tissue and smooth out wrinkles before the glue dries. Let it sit until dry, then trim off the excess with a new razor blade. Keep the tissue dry.

For the wings, spread the tissue flat on your work surface. Tissue grain will be perpendicular to the wing spars. Coat the top of the wing spars and pylon with glue and press the structure onto the tissue, keeping the tissue flat. Once the glue dries, trace and cut the wing outline.

Slide the free ends of the conrods onto the wing lever wires. The rear conrod must go on the left wing. Turning the crank should drive the wings in a smooth, symmetrical motion.

Cut two aluminum tube retainers 1/8" long and slip them onto the wing lever wires. Leave some space between the conrods and retainers. Crimp each retainer with pliers and add a small drop of glue to the outer end to hold it in place. As the conrods loosen up, you may need a retainer on the crank as well.

All that's left is to install the rubber band. Cut an 18" length of 1/8" model aeroplane rubber. Tie as shown. Apply rubber lube. Double the rubber band and hook it over the front and rear motor hooks, with the knot in the back. Your ornithopter is now ready for flight adjustments.

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