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Lesson 4e - Best L/D; Speed to Fly

Lesson Objective

The lesson will learn the concept of speed to fly -- the most appropriate speed given lift, headwind, tailwind or sink. 

Regulatory Requirement


  • Skyline Soaring Cockpit Cards contain polars for all club aircraft
    • Dual and Solo speeds for the two-seat gliders


  • Best L/D in still air for each aircraft
  • Skills to calculate the best L/D for a given headwind, tailwind, lift or sink
  • Compare with glide ratio at max L/D versus slower and faster speeds
  • Effect of the aircraft's weight and the glide ratio of the glider
  • Effect of the aircraft's loading and the max L/D speed 

Completion Standards

The student must be able to perform:

  • Calculations using a flight polar to determine the best L/D airspeed in the following circumstances:
    • still air
    • 10, 20, 30 knot headwind
    • 10, 20, 30 knot tailwind
    • 5 knots sink
    • 5 knots lift
    • Combinations of lift/sink and headwind/tailwind

The student must be able to explain:

  • The effect of loading and the max L/D speed

Prerequisite Study

Further Study

Next Lesson: 4f -- Boxing the Wake
Previous Lesson: 4d -- Slips: Forward, Side, Turning
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