Heavy Helicopters

Engineering Connection

For safety, speed and fuel efficiency, when designing recreation and transportation vehicles, engineers take into account all forces acting on the object. Engineers consider drag forces when they design land, air and water vehicles. When prototyping objects such as wings, windshields, propellers, helmets, sports equipment, or even an athlete's position, engineers use a wind tunnel to see the drag forces that are created around an object when air moves by, and they adjust their designs to minimize the amount of drag.

Materials List

Each group needs:

notebook paper, 8.5 x 11-inch size
10 paperclips
pencil
ruler
scissors
Helicopter Instructions Diagram, one per group
Heavy Helicopters Worksheet, one per student
measuring tape
stopwatch, such as smartphone or online stopwatch

Students make simple paper helicopters and test them with different weights.

Introduction/Motivation

When skydivers jump out of airplanes, the force that prevents them from accelerating towards the Earth in an uncontrolled way is drag. Drag acts in the direction opposite to motion. This opposing force slows down anything moving through the air.

You can feel drag if you stick your hand out a car window while the car is moving. It feels like a pressure pushing your hand backwards. The amount of drag that your hand creates depends on factors such as the size of your hand, the speed of the car and the density of the air. If you were to slow down, you would notice that the drag on your hand would decrease. If you change the position of your hand, you can increase or decrease drag by changing the amount of surface area facing the direction of movement.

The drag force generally increases for objects with large surface areas. For example, the large surface of a parachute helps a skydiver create more air resistance. We see many examples of drag reduction when we watch sporting competitions in the Olympics. Championship skiers, speed skaters and bicyclists squeeze down into a tight crouch. By making themselves "smaller," they decrease the drag they create, which enables them to move faster.

Drag exists because of the motion between a fluid (even air!) and an object. It doesn't matter if the object is stationary and the fluid is moving, or if the fluid is still and the object is moving through it. What really matters is the difference in speeds between the object and the fluid. This is why wind tunnels (an enclosed space with a stationary object surrounded by moving air) can be used to study the aerodynamics of objects—the drag forces are the same as if the object was moving and the fluid was still.

Procedure

Fold one sheet of paper in half lengthwise. (See steps 1-2 in Figure 1.)
Open the fold (step 3 in Figure 1) and cut along the folded line. (Step 4 in Figure 1.)
Take one of the halves and again fold it in half lengthwise. (Steps 5-6 in Figure 1.) Note: The other long half sheet does not get used, so it is available if students make a mistake with the first half.
Use a ruler to measure 4 inches from the left edge of the paper towards the center (as shown in the diagram). Then measure 2 inches after the 4 inches for the triangle and draw a triangle along the unfolded edge of the paper, as shown in the diagram.
Cut out the triangle. Be sure to cut through both layers of the paper (the top and bottom sides) (see steps 7-8 in Figure 1).
Open the paper (step 9 in Figure 1) and cut down the center of the paper from one edge of the paper to the starting point of the triangle. See pattern in the diagram and Figure 2.
Fold the tabs toward the center, as shown in Figure 3. Use a small piece of tape to secure the tabs. This serves as the helicopter base.
Now fold the blades along the dotted centered lines in opposite 90 degree directions, as shown in Figure 4. Doing this creates the helicopter propeller.
Test the helicopter to make sure it works.

Figure 1. The first folding and cutting steps to make a simple helicopter from a half-sheet of paper.

Figure 2. Where to cut to make the paper helicopter propeller blades.

Figure 3. Folding to make the paper helicopter base.

Figure 4. Final propeller folding steps to complete the paper helicopter.

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