What is the best glide angle speed at maximum weight with flaps in cruise configuration (KIAS)?

What is the best glide angle speed at maximum weight with flaps in cruise configuration (KIAS)?

• A. 60 KIAS
• B. 73 KIAS
• C. 55 KIAS
• D. 64 KIAS

Answer: (B)

Best glide speed is the airspeed that gives the maximum lift-to-drag ratio, so you get the greatest glide distance for a given altitude. At maximum gross weight the airplane must generate more lift, which shifts the L/D max speed higher compared to lighter weights. With flaps in cruise configuration (flaps up), the airplane’s drag characteristics favor a higher speed for the best L/D. For the Diamond DA20-C1 at maximum weight with flaps up, that optimum speed is about 73 KIAS, which provides the shallowest glide angle and the longest distance you can glide. Speeds much lower than that approach stall and reduce distance; speeds a bit higher than that increase drag and shorten the glide. So the 73 KIAS choice is the correct glide-speed for this setup.

Best glide speed is the airspeed that gives the maximum lift-to-drag ratio, so you get the greatest glide distance for a given altitude. At maximum gross weight the airplane must generate more lift, which shifts the L/D max speed higher compared to lighter weights. With flaps in cruise configuration (flaps up), the airplane’s drag characteristics favor a higher speed for the best L/D. For the Diamond DA20-C1 at maximum weight with flaps up, that optimum speed is about 73 KIAS, which provides the shallowest glide angle and the longest distance you can glide. Speeds much lower than that approach stall and reduce distance; speeds a bit higher than that increase drag and shorten the glide. So the 73 KIAS choice is the correct glide-speed for this setup.