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Principles of Rotary Flight

Last week we learned that an airplane can fly when its lift force is balanced with gravity. This week we will learn about another machine that can fly by producinglift balance gravity: the helicopter.

The Main Rotor

The lifting force of a helicopter is produced by the rotors. As rotors spin they cut into the air and produce lift, allowing the helicopter torise up. Each blade produces an equal share of the lifting force. Tilting the spinning rotor will cause flight in the direction of the tilt.

[pic]

The Tail Rotor

The tail rotor is used tocontrol the rotation of the helicopter. To explain this we need to understand the word torque. Torque is the name of a force that is always generated by any spinning object. When the helicopter rotorsare spinning, torque makes the body of the helicopter want to start spinning in the opposite direction that the rotors are spinning.
Obviously if this happens, the helicopter wouldn't be verycontrollable at all! By changing the angle of the tail rotor blades, the tail rotor can be used to make the helicopter turn left or right, like the rudder on a boat.

[pic]

In our experiment we willmake a paper helicopter that focuses mainly on the main rotor function: lift. Unlike a real helicopter, the paper helicopter can only provide enough lift to delay its fall, rather than actually enablingit to fly.

How to Build Paper Helicopters

Materials
• One piece of 8.5 x 11 inches piece of paper
• Scissors
• A ruler

Instructions
|Cut out a strip of paper about 90 X 15mm. |[pic] |
|With some scissors make a cut down half way down the middle of the strip.| |
|Make two small cuts, one-third of the way across the strip about 10mm below the end of the long cut. | |...