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Spies That Fly

Classroom Activity

Objective
To understand some of the challenges associated with building extremely small aircraft.

• copy of "Small, Smaller, Smallest" student handout ( HTML)
• copy of "Aircraft Templates" student handout (copied on 20-pound copier paper, 8.5-by-11 inches) ( HTML)
• large paper clip
• small paper clip
• stapler
• stopwatch

1. Tell students they are going to be downsizing an aircraft with a goal of making it as small as possible while still allowing it to fly.

2. Organize students into groups of at least three students and provide each group with a copy of the "Small, Smaller, Smallest" and "Aircraft Templates" student handout, the stopwatch, the paperclips, and the stapler. Set up testing areas (classroom corners are relatively free from crosscurrents). Place a stable chair in each site for students to stand on for flight tests.

3. Have each group construct the first aircraft, using the largest template on the page. Students should use the large paperclip to weight the bottom.

4. Students should test their models by dropping them from at least 2.2 yards (2 meters) above the floor. Make sure that someone is spotting the person on the chair for safety. Students should hold the helicopter at the top arm's length away and make the drops as consistent as possible.

5. Have the students drop each aircraft five times and find the average rate of descent (distance divided by time) for each different-sized aircraft. Have students record the time each flight takes in the chart on their student handouts.

6. Have students repeat the test with the two smaller aircraft, using the small paperclip for the medium-sized aircraft, and the two staples for the smallest one.

7. After completing testing, have the groups report their findings for the various-sized models. Have students compare the data across groups for all of the same-sized models. Is there is a wide variance of results from one group to another? If so, what might explain these differences? What general conclusions can students make regarding the effect(s) of scaling down a model?

8. As an extension, create an overhead transparency of the student page grid. Project it on a piece of paper on the wall and have students create an aircraft larger than their original design. Then have them think of a suitable weight to use for the bottom, and measure the rate of descent. How does the larger model compare to the smaller ones?

Machines reach a limit of their function for two main reasons: size and construction materials. The wings of today's aircraft are built to be flexible. If they were not, wings would break under the tremendous stresses of flying. Engineers focus on designing wings that have the maximum strength given the wing area needed to lift the airplane. In the students' models, the surface area/density ratio of paper changes as smaller aircraft are constructed. Since the density of the paper is constant, the aircraft becomes relatively stiffer and less flexible as it is built smaller.

Here is a sample set of data for the activity:

The pull of gravity is constant on all bodies, regardless of their mass. In the case of the students' models, surface area (and the resulting wind resistance) is the key feature that acts to change the performance of the aircraft as it is built to different dimensions.

Book

Dudley, Robert. The Biomechanics of Insect Flight: Form, Function, Evolution. Princeton, NJ: Princeton University Press, 2000.
Explains insect morphology, wing motion, aerodynamics, flight energetics, and flight metabolism.

Articles

Dupont, D. "In Plane Sight." Scientific American, September, 20, 1999.
Discusses the role UAVs played in operations over Kosovo and the advantages and disadvantages of flying without a pilot.

Glaskin, M. "Disc-shaped Spyplane Could Hunt for Terrorists."
www.newscientist.com/news/news.jsp?id=ns99991859
Features the small, disc-shaped SiMiCon Rotor Craft, which can take off vertically, hover, and fly forward at high speed.

Kunzig, R. "The Physics of Insect Flight: What's the Buzz?" Discover, April 2000.
Online at: www.discover.com/issues/apr-00/departments/featphysics/ Reviews the evolution of insect flight and methods scientists use to learn how insects fly.

Web Sites

CAMCOPTER® Unmanned Aerial Vehicle System
www.schiebel.net/pages/cam_intro.html
Describes a miniature spy plane that flies like a helicopter, including the aircraft's maximum mission radius, tank volume, and cruise speed.

RQ-1 Predator Unmanned Aerial Vehicle
www.af.mil/news/factsheets/RQ_1_Predator_Unmanned_Aerial.html
Describes the background, features, and characteristics of the Predator.

UAV Capabilities
uav.wff.nasa.gov/CapabilitiesChart.cfm
Provides a chart comparing UAVs in terms of payload weight, endurance, and altitude capability.

The "Small, Smaller, Smallest" activity aligns with the following National Science Education Standards.

Grades 5-8

	Science Standard B: Physical Science

Motions and forces

• The motion of an object can be described by its position, direction of motion, and speed. That motion can be measured and represented on a graph.

• An object that is not being subjected to a force will continue to move at a constant speed and in a straight line.

Grades 9-12

	Science Standard B: Physical Science

Motions and Forces

• Gravitation is a universal force that each mass exerts on any other mass. The strength of the gravitational attractive force between two masses is proportional to the masses and inversely proportional to the square of the distance between them.