Early in our pilot training we learn about two of these “V-speeds” that are often quoted and used during departure—they are V_X and V_Y. When planning a departure, pilots should consider the airport environment and determine at what speed to climb based on how quickly the airplane must gain altitude to ensure safety of flight.

At one end of the single runway at my home airport, there are trees and gradually rising terrain. Because of those obstacles, when departing in that direction I always use my aircraft’s V_X climb speed. Also known as the “best angle of climb” speed, V_X is the speed at which the airplane gains the most altitude over a short distance. It is a steeper angle of climb, and at a lower airspeed, than V_Y.

V_Y is the “best rate of climb” speed. At this speed, the aircraft will climb to altitude quickest. This is the speed to use on climb-out if there are no obstructions to consider that would require a steeper angle upon departure.

Generally, the rule of thumb is to use V_X as needed on takeoff and then pitch down slightly after obstruction clearance to continue climbing at V_Y. Upon reaching V_Y, that speed would be maintained until the predetermined altitude is reached and the pilot levels the aircraft off, and transitions to cruising airspeed.

The best takeoff technique to use will depend on your aircraft and the departure airport. For example, if the runway requires a short-field takeoff technique, you may routinely climb out at V_X before continuing the climb at V_Y. The appropriate procedure for your aircraft will be found in the pilot’s operating handbook or airplane flight manual.

Additional information about V_X and V_Y can be found in Chapter 6 of the FAA’s Airplane Flying Handbook.