What is the significance of Vx and Vy speeds, and how do they differ?

• A. Vx is best angle of climb (highest altitude per distance); Vy is best rate of climb (maximum altitude per unit time).
• B. Vx is best rate of climb; Vy is best angle of climb.
• C. Vx is maximum speed; Vy is minimum speed.
• D. Vx is best glide speed; Vy is best endurance speed.

Answer: (A)

Vx and Vy describe two different climb performance goals. Vx is the speed that gives the steepest climb path—the greatest gain in altitude for each unit of horizontal distance traveled. It’s used when you need to clear obstacles or gain height quickly over a short horizontal run. Vy, on the other hand, is the speed that yields the maximum rate of climb—your fastest vertical gain per unit of time. At Vy you reach altitude as quickly as possible, though the climb path is not as steep.

The key difference is altitude gained per distance versus altitude gained per time. That’s why Vx is the best angle of climb, while Vy is the best rate of climb. The speeds differ because drag and thrust balance change with airspeed, so the fastest altitude gain per second doesn’t occur at the same speed as the steepest climb per mile.