1. how lift, drag, thrust, and gravitational forces affect airborne objects,
2. how thrust forces are produced,
3. how energy, momentum, and mass figure into propeller, jet, and rocket propulsion.

1. As one of these pilotless planes maintains level flight on a windless day, gravity pulls downward on the plane and continuously transfers downward momentum to it. (A) What does the plane do with this downward momentum to avoid descending? (B) How does the plane actually carry out this task (i.e. dealing with the downward momentum)?

2. Although the pilotless plane manages to maintain level flight through the still air, it continuously loses energy to that air. Look at the dynamics of the air itself to show that this energy loss must occur, even if the plane does not experience any viscous or pressure drag.

3. To remain above a particular city, the pilotless plane flies in a slow, level circle centered high above the city hall. What exerts the centripetal force that allows the plane to undergo uniform circular motion? Explain.

4. In order to circle above city hall, the plane has to lower its inside wing (the wing that's closest to city hall). The plane thus flies with a slight tilt--its outside wing higher than its inside wing. How does this tilt lead to the plane's circling motion?

5. To make efficient use of its limited solar energy, the pilotless plane flies relatively slowly. Its wings are highly curved and nonsymmetrical--they bow significantly upward in the middle, between their leading edges and trailing edges. (A) How does this wing shape affect the air pressures above and below each wing and enable the plane to fly so slowly? (B) How would this wing shape affect the plane's ability to maintain level flight while inverted (upside-down)?

6. To make efficient use of its solar power, the slow-moving plane uses big propellers rather than jet engines. These propellers push large volumes of air backward to obtain their forward thrust. In the process, this air picks up a small backward speed. While the same amount of thrust could be obtained with a jet engine that pushes small volumes of air backward and gives that air a large backward speed, the jet engine would be less energy efficient. Why?

7. The higher the pilotless plane goes, the more trouble it has maintaining level flight. With its solar panels providing steady and renewable energy, something else must be limiting its altitude. (A) What actually limits the plane's maximum altitude? (B) Why would having small rocket engines onboard only temporarily increase the plane's maximum altitude? (Neglect the small increase in maximum altitude that comes with reducing the plane's total weight.)

8. To leave the earth's atmosphere completely, the pilotless vehicle would have to rely on rocket thrust instead of airplane engines. But with no atmosphere to push against, how could even a rocket-powered pilotless vehicle propel itself forward?