This project involves the design, fabrication, and testing of simple "systems" which will defy gravity by staying in the air as long as possible and traveling as far as possible from the launch site. Students construct their systems from a limited set of common materials and ordinarily launch their designs by hand from some elevated location. The project helps students understand several principles of aerodynamics and can be done by students at any stage of their education. It is quite safe and lots of fun.
The purpose of this project is to give students a chance to think about and create solutions to a problem related to those of practical air transportation. Essentially, the problem is one of minimizing and overcoming the unwanted effects of gravity while having an enjoyable, successful experience in the process. Students are expected to gain some practical feel for the principles and relations involved and to gain an understanding of the process of design in which compromises are made to maximize performance while satisfying various practical constraints.
Gravity is an ever present part of life, often essential to achieving our goals, sometimes a serious obstacle, and sometimes just a nuisance. Engineers are continually challenged to design systems and devices that use gravity and avoid the problems that it causes. In this project students are challenged to conceive and fabricate (from a limited set of materials) a system that will use principles of aerodynamics and relations between gravity forces, aerodynamic forces, areas, volumes, and material properties to achieve specified goals common in real transportation systems.
Design and fabrication activities are generally suited to an indoor tabletop situation. A flat, nine square foot size work space is probably adequate for each individual or team project.
Testing, on the other hand, requires considerable space and is probably best done outdoors. The main requirement is for an extended open space (perhaps 100 feet square). It is also highly desirable to have an elevated launch site. Second or third story exposed stairs, a tower, roof access, bridge, or most any safe elevated locations are usable. The amount of time involved is quite flexible. The minimum time is about three hours, either in a block or in three segments. This can be expanded to perhaps five hours, which could include time at home to think about the project and each team/individual building several models. We have found that this project can be repeated once with good results. The first time through, students see many new issues, develop new questions, and generate ideas which they don't have time to explore. By giving them "another chance," they can refine their ideas and explore new ones. The second time through, students find a significant improvement in the performance of their designs. Often students with a poor first attempt have some of the better second attempts.
In this project the students are limited to a small set of materials. In particular, the systems which they fabricate and test may contain no materials other than cellophane (Scotch-type) tape (3 ft. limit), plastic (Saran-type) film (5 sq. ft. limit), string (10 ft. limit), aluminum foil (4 sq. ft. limit), spaghetti (20 piece limit), cardboard (2 sq. ft. limit), metal paper clips (10 piece limit), plastic drinking straws (5 each limit), and chewing gum (new or used, 1 piece limit).
No equipment limitations are placed on the students. It probably would be adequate to ensure that there is a good supply of scissors and rulers available. You will also need a stop watch and a 50 foot tape measure for scoring. (You might want to borrow one from the athletic department.)
For this project we recommend teams of two to five students that generate ideas. Although teams are desirable, this project can also be done by individuals. Once the teams have developed different concepts, we suggest the teams build several models of perhaps their "best" idea with different materials. It is a good idea to encourage each student in a team to be actively involved in the building process, even if they build similar models. We suggest that the teams meet together to discuss principles and ideas and then have each member fabricate one or more systems for testing.
It is advisable to encourage the students to test their designs before they submit them for performance testing. They do not need to test the models from your designated launch sight. Instead, they can test them in a controlled environment like their classroom or a hallway. In our studies, we have found that students tend to "complicate" their designs in that they design very intricate, complicated systems attempting to maximize each goal. These designs take considerable time to build, and unfortunately, often do not work as intended and end up surprising the student designers. Secondly, students tend to add material to designs instead of removing material. By adding material, they increase the weight of their designs, which usually reduces its performance.
The best way to both encourage students and head off disappointment is to require that each team give you a quick "presentation" of their ideas. This can consist of drawings or just giving each member a chance to comment on their design. Make sure that the students understand the concepts discussed in the student handout by asking them related questions. Giving students constructive hints like encouraging testing while building, focusing on simple designs, and removing material instead of adding material will make them think more about their designs without restraining or limiting their natural creative talents.
The main tasks are to find a suitable place for testing and to gather the necessary materials and equipment. The test or launch site should be at least one or two stories high if possible and should have a substantial guard rail for safety. Also, seek a location where there will be open space without stray people wandering through or trees that may capture a good design. This project tends to attract an audience and you need to think about how to deal with them. Although the project testing is very safe, an audience could distract and interfere with the tests.
The quantities of materials needed can be calculated based on the amounts per system and the number of students. Allow one set of materials as listed above for each student. Note that the amounts given are for practice as well as final versions of their systems. If you plan on giving the students a chance to redesign, then you will need additional materials; however, you will not need double the materials since students will not use all their allotment and much can be reused. You will also need a pair of scissors and a ruler for each two or three students during fabrication. In addition you will need some sort of a stop watch (many digital watches have this feature) to measure flight duration and a tape measure to establish flight distance.
We recommend the following approach:
Divide the group into teams (two to five students per team is prefered) and have the teams move so that they are sitting together.
Distribute the project description document to each student.
Present the project to the students.
Provide the students with about 30 to 45 minutes to read the materials, to discuss the principles, and to generate design ideas.
Give the students the working materials.
Give the students from 60 to 120 minutes to fabricate and test prototype designs.
ormally test the systems produced (one per team if the group is large or if time or space are limited, one per student otherwise). Since environmental conditions may vary and some design will greatly depend on the launch, it is a good idea to test each design several times and take the average score of the tests.
Discuss the results of the testing, emphasizing the reasons for differences in performance (done immediately after testing if time allows for best impact).
Repeat items 5-8 with new materials if time permits.
Spend a few minutes summarizing the results of the project and providing closure.
Systems may be tested individually or simultaneously. If the total number of designs is small (less than ten), then individual testing can be done. Students, most likely, will greatly enjoy the testing process. Often individual rivalries will develop and can be constructive; however, all students should be encouraged and efforts be acknowledged. If time allows, test each design several times. Depending on environmental conditions and design types, students might observe a wide performance range.
Individual testing of each design allows others to observe each different design's performance, often a good learning experience in itself. If time does not allow individual testing or if you think individual testing might tend to drag, then simultaneously testing all designs is more exciting (you will need someone with a timing capability for each system).
You will need an assistant to help you time, measure distances, and record results. It is best if you control the timing and record results since this also gives you an opportunity to write comments about each design. A student volunteer who is not actively involved with their team's testing is a good candidate to help measure. Another faculty member or teaching assistant could also help.
Note that we have defined two distinct performance criteria, a Basic Performance Requirement (BPR) and an Extra Performance Index (EPI) as described in the student materials for this project. The intention is that almost all students will achieve the BPR and thus feel that they have succeeded. Please encourage them to feel successful and good about their efforts. The EPI allows recognition of superior performance and handles the competition that seems to arise naturally. We suggest that you do not make a big deal out of the competition and seek rather that everyone end up feeling that they are a winner.
There are many examples of real-world systems, both natural and manufactured, which do indeed fly through the air. Ordinarily these systems rely on some combination of initial velocity, thrust from a source of power, aerodynamic lift from surfaces, light weight, and maximization of the ratio of surface forces to gravity forces. Note that surface forces are generally proportional to the area while gravity forces are proportional to the mass. Consideration of these principles commonly leads to one of the following four basic concepts:
A "ballistic missile", which focuses on initial velocity.
A "glider" which seeks to utilize the aerodynamic lift of wings.
A "parachute", which utilizes aerodynamic lift and drag to slow decent.
A "seed" which is very small and uses the fact that as size goes down, the ratio of surface forces to gravity forces goes up.
In addition, there are often hybrid or combination designs, for example, a parachute which is thrown high in the air before opening. Concept #1 generally involves a reasonably small but dense projectile. Concepts #2 and #3 generally seek to create a wing system with a very large area and low weight. Concept #4 involves a very tiny system (just a piece of lint is excellent), which naturally has a very high aerodynamic drag to weight ratio. If the wind is blowing in the right direction, concept #4 works particularly well.
The student materials for this project discusses aerodynamic forces in greater detail; however, we have found that younger, less experienced students benefit from discussing these four basic design classes before designing and building their own systems. For more advanced students, giving them these four basic classes seems more likely to hinder their creativity.
We encourage you in this project to emphasize that effective design is the application of suitable principles to achieve specified goals. Reviewing the principles listed above should prove helpful to the students. Finally, please make a special point of reminding the students that this kind of creative activity (i. e., meeting goals by using physical principles and building a design using limited, "unusual" materials) is at the heart of engineering and that, if they found the project enjoyable, they should consider engineering as a profession.
The main concern here is that no one fall from the launch platform. Be sure that there is a good guard rail and that the students don't get so caught up in the project that they forget to be careful. Students are also at risk when they cut and shape their materials using scissors. We can never remind the students enough to work carefully and consciously.
This project was developed by John Garcelon.