http://www.instructables.com/id/DIY-AIR-POWERED-CAR/

This is how to make an air powered car with simple materials.

• a motor w/ a battery
• a fan/propeller
• wheels
• a plastic bottle
• a plastic shaft
• a hot glue gun

Cut holes in the bottle for the plastic shafts to fit into the bottle.

Fit and glue the wheels on the shaft after the shaft is through the bottle.

Attach the motor and the propeller/fan at the end of the bottle. While doing that, put a switch at the front of the car to turn on the battery which powers the motor and the propeller/fan.