The Propeller

Rubber band powered propeller

The second vehicle, the plane, is powered by a rubber band propeller (pictured right). The whole propeller is made of a bamboo skewer, wire, plastic, beads, and rubber bands.

Indication of the angle
of the blades

The blades are made of plastic, cut and tilted to be as similar to a normal propeller as possible. One of the problems we had in the initial design of the propeller was that it wasn't pushing enough air out for the plane to sustain motion. After studying some propellers, we changed from having straight flat blades to blades that tilt downwards on opposing sides (as shown in the photos). 
The angle of the blades allows more air to pass underneath creating a "lift". 

Additions on the spinner

The blades are connected with wire to the "spinner". The connection consists of two interlocking loops of wire. The wire perpendicular to the blades extends through the plastic tube which allows it to spin freely while being attached to the bamboo skewer.  
With the initial design, the most problems were with the spinner. The wire holding the blades kept tipping back and forth as the connection wasn't tight enough and would move. Also, the rotation of the spinner was very rough due to the friction created between the looped wire and the plastic tube. The problems were resolved by two things. Firstly, I wrapped a thinner wire around the joint to secure the loops of wire to restrict the movement. Secondly I added two beads between the joint and the plastic tube greatly reducing the friction between them. 
The speed of the propeller was an issue. To try and increase the speed of the propeller, I tried to change the number and thickness of the rubber bands. I found that with a greater number of thicker rubber bands would significantly increase the speed of the propeller. 

W Y Chan