Rate of climb
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In aerodynamics, the rate of climb RoC is the speed at which an aircraft increases its altitude. In the United States, this is most often expressed in feet per minute and can be abbreviated to ft/min. Elsewhere, it is commonly expressed in metres per minute, abbreviated as m/min.
The rate of decrease in altitude is referred to as the rate of descent or sink rate.
There are two traditional airspeeds for most aircraft relating to rates of ascent, referred to as Vx and Vy.
Vx refers to the "best angle of climb speed,"FAR which is usually less than Vy, the "best rate of climb speed."FAR The difference between these speeds relating to the rate of climb lie in the climb objective.
Climbing at Vx will allow a pilot to maximize the vertical speed per unit ground distance. That is, Vx will allow you to maximize your climb while sacrificing the least amount of ground distance. This occurs at the speed for which the difference between thrust and drag is the greatest (maximum excess thrust). In a jet airplane, this is approximately minimum drag speed, or the bottom of the drag vs. speed curve. Climb angle is proportional to excess thrust.
Climbing at Vy will allow a pilot to maximize the vertical speed per unit time. That is, Vy, will allow you to maximize your climb while sacrificing the least amount of time. This occurs at the speed for which the difference between engine power and the power required to overcome the aircraft's drag is the greatest (maximum excess power). Climb rate is directly proportional to excess power.
The indicated airspeeds of Vx increases with altitude and Vy decreases with altitude, indicating that Vx = Vy at a certain airplane's absolute ceiling.
The initial rate of climb record for pilot aircraft is held by Mig-29 at 330 m/s (65,000 ft/min). The average rate of climb for a MiG-29 is only 109 m/s 0-6000 m. [1]
