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

• Pre-Solo: 14 CFR §61.87(i)(8)
• Private Pilot Candidate: PTS V(B)

Materials 

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

Content

• 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

• Glider Flying Handbook (2024), Chapter 3, page 3-6 "Glide Ratio"
• Glider Flying Handbook (2024), Chapter 5, page 5-8 "Glider Polars"
• Glider Flying Handbook (2024), Chapter 11, pages 11-1 through 11-16 

Further Study

• Glider Polars and Speed-to-Fly; Wander Books (Available through the club, and online )