Things to Emphasize

1. For any object to be aerodynamically stable when moving through any fluid, its centre of mass must be ahead of the object's centre of pressure.
2. A object's centre of mass can be moved by adding or removing mass from the object or by redistributing the mass within the object.
3. An object's centre of pressure can be moved by adding or removing fins to the object.
4. In general, centre of mass depends upon the composition and structure of an object, whereas, centre of pressure depends only on the shape of the object.

1. Build a simple paper airplane.
   1. Attach a large paper clip to the front of the airplane.
      

   2. Throw the airplane and measure the distance it travels. Also record its flight behavior.

   3. Attach the paper clip to the middle of the airplane.
      Repeat step b.

   4. Attach the paper clip to the end of the airplane.
      Repeat step b.

   5. Try flying the airplane backwards as set up in step d. Repeat step b

2. All manufacturers of airplanes have specific regulations which tell exactly how the cargo in each airplane that they sell must be loaded. Why is this?

   ANSWER: All airplanes, big and small, could be loaded with cargo or passengers so that the centre of mass (also called the centre of gravity) of the airplane moves too far back , towards the tail of the airplane. When this happens the airplane can become aerodynamically unstable! In certain cases this condition can arise while the aircraft is in flight. Most airplanes store fuel in their wings, the bulk of which is well ahead of the airplane's centre of pressure. As the airplane's fuel load decreases, the centre of mass can gradually move backwards , towards the tail. As the fuel load decreases in a poorly loaded airplane, the aircraft can suddenly, and often without warning, become aerodynamically unstable.

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