Two Ways to Describe Lift: teacher key

Airplanes, grade 12 edition, written for 12th grade and up. Pressure or Newton? Lift has two correct descriptions, one popular wrong one, and a real argument about which is the cause. Follow it through the Smithsonian, jet thrust, autopilots and the Concorde's economics.

Read the book. Print this page for the key.

Questions and answers

1. Which two positions do people who argue about lift fall into?
   • Pressure difference (Bernoulli) and reaction force (Newton) (answer)
   • Weight and thrust
   • Wing shape and engine size
2. What does NASA Glenn call the equal transit time idea?
   • The Wright brothers' theory
   • The first correct theory of lift
   • The most popular incorrect theory of lift (answer)
3. According to the Smithsonian's How Things Fly, what is the downwash behind a wing?
   • The same thing as thrust
   • An effect of lift rather than the cause (answer)
   • The cause of lift
4. What is the basic source of thrust, according to the Smithsonian?
   • Pressure (answer)
   • Weight
   • Gravity
5. What does an autopilot system consist of?
   • A single propeller
   • A set of gyroscopes only
   • Servo actuators plus control circuits (answer)
6. What happened to the Concorde's small market as parts became harder to get?
   • It stayed the same
   • It shrank (answer)
   • It doubled

Words

• downwash: air pushed down
• viscosity: air's friction
• servo: control mover
• gyroscopes: spinning direction sensors
• compressibility: air squeezability