Aircraft Performance

tsurhT Velocity (TAS) tsurhT LEGEND T thrust E excess (Full PCL) T A thrust (Full Throttle) T T available A A T thrust R T required E T T AOC angle of R E T climb Max AOC (jet) R TAS true airspeed L/D lift to drag MAX L/D L/D ratio MAX MAX maximum Max AOC (prop) PCL power control lever Velocity (TAS) Figure 11-8. Comparison of maximum AOC between jet and propeller airplanes. edutitlA to altitude (PE); the airspeed decreases to something less so as to achieve maximum altitude increase with minimum than 120 knots as the altitude increases. horizontal travel over the ground. A good use of maximum AOC is when taking off from a short airfield surrounded by There are two primary reasons to evaluate climb performance. high obstacles, such as trees or power lines. The objective is First, aircraft must climb over obstacles to avoid hitting to gain sufficient altitude to clear the obstacle while traveling them. Second, climbing to higher altitudes can provide the least horizontal distance over the surface. better weather, fuel economy, and other benefits. Maximum Angle of Climb (AOC), obtained at V , may provide climb One method to climb (have positive AOC performance) is X performance to ensure an aircraft will clear obstacles. to have excess thrust available. Essentially, the greater the Maximum Rate of Climb (ROC), obtained at V , provides force that pushes the aircraft upward, the steeper it can climb. Y climb performance to achieve the greatest altitude gain over Maximum AOC occurs at the airspeed and angle of attack time. Maximum ROC may not be sufficient to avoid obstacles (AOA) combination which allows the maximum excess in some situations, while maximum AOC may be sufficient thrust. The airspeed and AOA combination where excess to avoid the same obstacles. [Figure 11-7] thrust exists varies amongst aircraft types. As an example, Figure 11-8 provides a comparison between jet and propeller Angle of Climb (AOC) airplanes as to where maximum excess thrust (for maximum AOC is a comparison of altitude gained relative to distance AOC) occurs. In a jet, maximum excess thrust normally traveled. AOC is the inclination (angle) of the flight path. For occurs at the airspeed where the thrust required is at a maximum AOC performance, a pilot flies the aircraft at V X minimum (approximately L/D MAX ). In a propeller airplane, maximum excess thrust normally occurs at an airspeed below L/D and frequently just above stall speed. MAX Rate of Climb (ROC) ROC is a comparison of altitude gained relative to the time needed to reach that altitude. ROC is simply the vertical component of the aircraft’s flight path velocity vector. For maximum ROC performance, a pilot flies the aircraft at V Y C so as to achieve a maximum gain in altitude over a given O R O C Max period of time. A ax M Maximum ROC expedites a climb to an assigned altitude. This gains the greatest vertical distance over a period of time. For example, in a maximum AOC profile, a certain Distance aircraft takes 30 seconds to reach 1,000 feet AGL, but covers only 3,000 feet over the ground. By comparison, Figure 11-7. Maximum angle of climb (AOC) versus maximum rate using its maximum ROC profile, the same aircraft climbs of climb (ROC).