Best L/D; Speed to Fly

Lesson Objective

Regulatory Requirement

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

Materials 

• ASK-21 Polar
  
• Grob G-103 Polar (use the flight manual)
  
• Sprite SGS 1-36 Polar (use the flight manual)
  

Content

• Best L/D in still air for each aircraft
• Skills to calculate the best L/D for a given headwind or tailwind
• Ability to calculate the best L/D speed given a sinking airmass
• 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

• 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 Flight Manual, "Best L/D" Page 7-34
• Glider Flight Manual, "Speed-to-Fly" Page 7-34
• Glider Flight Manual, "Glider Polars" Page 5-6
• Glider Flight Manual, "Effects of Water Ballast" Page 5-13

Further Study

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

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