Aircraft Performance

rewoP Velocity (TAS) rewoP to 1,500 feet in 30 seconds but covers 6,000 feet across the to minimize the weight, since it has such a marked effect on ground. Note that both ROC and AOC maximum climb the factors pertaining to performance. profiles use the aircraft’s maximum throttle setting. Any differences between max ROC and max AOC lie primarily A change in an aircraft’s weight produces a twofold effect in the velocity (airspeed) and AOA combination the aircraft on climb performance. First, a change in weight changes the manual specifies. [Figure 11-7] drag and the power required. This alters the reserve power available, which in turn, affects both the climb angle and ROC performance depends upon excess power. Since the climb rate. Secondly, an increase in weight reduces the climbing is work and power is the rate of performing work, maximum ROC, but the aircraft must be operated at a higher a pilot can increase the climb rate by using any power not climb speed to achieve the smaller peak climb rate. used to maintain level flight. Maximum ROC occurs at an airspeed and AOA combination that produces the maximum An increase in altitude also increases the power required excess power. Therefore, maximum ROC for a typical jet and decreases the power available. Therefore, the climb airplane occurs at an airspeed greater than L/D and at an performance of an aircraft diminishes with altitude. The MAX AOA less than L/D AOA. In contrast, maximum ROC for speeds for maximum ROC, maximum AOC, and maximum MAX a typical propeller airplane occurs at an airspeed and AOA and minimum level flight airspeeds vary with altitude. As combination closer to L/D . [Figure 11-9] altitude is increased, these various speeds finally converge MAX at the absolute ceiling of the aircraft. At the absolute ceiling, Climb Performance Factors there is no excess of power and only one speed allows steady, Since weight, altitude and configuration changes affect level flight. Consequently, the absolute ceiling of an aircraft excess thrust and power, they also affect climb performance. produces zero ROC. The service ceiling is the altitude at Climb performance is directly dependent upon the ability to which the aircraft is unable to climb at a rate greater than 100 produce either excess thrust or excess power. Earlier in the feet per minute (fpm). Usually, these specific performance book it was shown that an increase in weight, an increase in reference points are provided for the aircraft at a specific altitude, lowering the landing gear, or lowering the flaps all design configuration. [Figure 11-10] decrease both excess thrust and excess power for all aircraft. Therefore, maximum AOC and maximum ROC performance The terms “power loading,” “wing loading,” “blade loading,” decreases under any of these conditions. and “disk loading” are commonly used in reference to performance. Power loading is expressed in pounds per Weight has a very pronounced effect on aircraft performance. horsepower and is obtained by dividing the total weight If weight is added to an aircraft, it must fly at a higher AOA of the aircraft by the rated horsepower of the engine. It to maintain a given altitude and speed. This increases the is a significant factor in an aircraft’s takeoff and climb induced drag of the wings, as well as the parasite drag of the capabilities. Wing loading is expressed in pounds per square aircraft. Increased drag means that additional thrust is needed foot and is obtained by dividing the total weight of an airplane to overcome it, which in turn means that less reserve thrust is in pounds by the wing area (including ailerons) in square feet. available for climbing. Aircraft designers go to great lengths It is the airplane’s wing loading that determines the landing LEGEND P power E excess P power A available (Full PCL) P power (Full Throttle) R required P A ROC rate of P P P climb A E R P TAS true E P airspeed R L/D lift to drag MAX ratio maximum L/D MAX Max ROC (jet) L/D Max ROC (prop) MAX PCL power control lever Velocity (TAS) Figure 11-9. Comparison of maximum ROC between jet and propeller airplanes.