Why Winglets?

Objective

The goal of this project is to measure the effects on flight performance when winglets are added to a paper airplane design.

Introduction

The Boeing jet in the picture at right has winglets at the tips of its wings. Why are they there? What do they do?

As an airplane moves through the air, the wings generate lift by creating an area of low pressure above the upper surface of the wing. The higher air pressure beneath the lower surface of the wing lifts the plane. At the tip of the wing, the high and low pressure air meet.

Diagram of wing tip vortices from a passenger jet.

Figure 1. The diagram shows the expanding wing tip vortices generated by a passenger jet. (NASAexplores.com, date unknown)

The air forms miniature tornadoes, called wing tip vortices that spread out behind the plane (see Figure 1, right). Wing tip vortices cause two problems:

the turbulent airflow they create can be strong enough to flip an airplane that encounters it;
they also increase the drag forces on the airplane that generates them, decreasing fuel efficiency.

Winglets break up wing tip vortices, alleviating both of these problems.

In this project, you will test paper airplanes built both with and without winglets and measure the effect on flight performance. When doing your background research, you should also study vertical stabilizers. In the simple designs used in this project, winglets will also function as vertical stabilizers.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

fuselage,
airfoil,
winglets,
vertical stabilizer,
horizontal stabilizer,
drag,
lift,
center of lift,
center of gravity,
wing tip vortices.

Questions

What are the three forces acting on a glider in flight?
What relationship between these forces is needed for stable flight?
How will the addition of winglets affect these forces?
How will the addition of winglets affect flight performance?

Bibliography

You'll definitely want to check out the Gliders section (among others) of NASA's Beginner's Guide to Aeronautics. This site is packed with useful information on the science of flight:
NASA, 2005a. "Guided Tours of the Beginner's Guide to Aeronautics," NASA, Glenn Research Center [accessed June 8, 2006] http://www.grc.nasa.gov/WWW/K-12/airplane/guided.htm.
Here are two links with alternative designs for folded paper airplanes. The second link (Palmer, 2000) has an excellent plan (PL-1, "Joe's Favorite") for testing with and without winglets:
- NASA, 2005b. "Folding Paper Airplane: How To Build a JET Model," NASA Glenn Research Center [accessed June 8, 2006] http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/foldairplane.html.
- Palmer, J., 2000. "Joseph Palmer's Paper Airplanes," [accessed June 15, 2006] http://www.josephpalmer.com/planes/Airplane.shtml.
Here are some sources of information on winglets:
- NASAexplores, 2002. "Taming Twin Tornadoes," NASA's Aeronautics Mission Directorate, NASAexplores.com [accessed June 8, 2006] http://www.nasaexplores.com/show2_articlea.php?id=02-025.
- Larson, G.C., 2001. "How Things Work: Winglets," originally published in Air & Space/Smithsonian, Aug/Sep 2001, available online: http://www.airandspacemagazine.com/ASM/Mag/Index/2001/AS/htww.html.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

paper for making airplanes,
tape measure to measure flight distance,
an indoor location with open space to test-fly the planes.
Optional: stop watch to measure flight time.

Experimental Procedure

Do your background research so that you are knowledgeable about the terms, concepts, and questions above.
Start with your favorite paper airplane design. Figure 2, below, shows one popular model (see the first suggestion in the Variations section, below, for ideas on optimizing the design). This NASA link has another design you can try: http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/foldairplane.html.
Figure 2. The simple, classic folded paper airplane.
Using your chosen design, build several identical paper planes.
Test-fly each plane at least 5 times, and measure the distance flown. Be careful to launch the planes at the same angle, and with the same amount of force each time. Note any instabilities in the flight characteristics (nose dives, rolling, turning). Optional: you can also use a stop watch to measure the flight duration. Keep track of the data in your lab notebook.
Fold a small portion of each wing tip up to create equal-sized winglets on each wing, and repeat the test flights.
Calculate the average flight distance for each plane, both with and without winglets.
Did flight distance improve with winglets? Were there improvements in other flight characteristics?

Variations

Experiment with the design of the simple folded airplane to optimize the flight characteristics before trying winglets. For example, you can shorten the plane by folding back a portion of the nose before folding up the wings (step 3 in Figure 2, above). (What effect does this have on the center of gravity? What effect does this have on the center of lift?) You can alter the surface area of the wings slightly by experimenting with exactly where to place the fold in step 4 of Figure 2. Test your designs with multiple flight tests and keep track of the results in your lab notebook. Then use your best design to see if winglets improve performance even further.
Experiment to find the optimal size for winglets.
Does it matter if you fold the winglets down or up?
The simple folded airplanes used in this project normally lack vertical stabilizers. Vertical stabilizers resist forces that would tend to make the plane yaw (nose moving from side to side). In this simple type of paper airplane, winglets can function as vertical stabilizers. Another type of paper airplane (made with laminated construction methods) generally does include a vertical stabilizer as part of the design. For more details, see the Science Buddies project What Makes a Good Aerodynamic Design? Test Your Ideas with High-Performance Paper Gliders. Do winglets improve the flight characteristics of high-performance paper gliders?
For a more advanced project on winglets using a wind tunnel, see the Science Buddies project Winglets in Wind Tunnels.

Sources