Q. Why is VX different from VY?
A. Pilots fly at the airplane?s maximum rate of climb airspeed ? VY ? when they want to gain the most altitude in the shortest time, and the climb angle isn?t important. They fly at the maximum angle of climb airspeed ? VX ? when they want to climb at the steepest possible angle without regard for climb rate, such as when they must clear an obstacle immediately after takeoff, for example. In both cases we?re assuming the pilot is using full power and holding a steady airspeed.
Figure 1 shows two identical airplanes 30 seconds after they?ve taken off from the same point on the runway. Airplane Y, flying at VY, has traveled farther and gained more altitude than Airplane X. Airplane X achieved its steeper climb-out angle by flying at the slower VX airspeed. VX is always slower than VY, except at the airplane?s absolute ceiling where they are the same.
Ed Kolano
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