AC performance

Chapter 11: Aircraft Performance

11-1 Introduction

• Factors affecting aircraft performance:

  • Aircraft weight

  • Atmospheric conditions

  • Runway environment

  • Fundamental physical laws of forces acting on an aircraft

• Importance of Performance Data:

  • Found in Aircraft Flight Manual/Pilot’s Operating Handbook (AFM/POH)

  • Includes data on takeoff, climb, range, endurance, descent, and landing

  • Mandatory for safe and efficient operations

  • Familiarity with AFM/POH enhances knowledge of aircraft operations

11-2 Atmospheric Pressure

• Standard sea level pressure:

  • 29.92 inHg or 1013.2 mb

• Variability of manufacturer data in AFM/POH:

  • Data may be provided in tables or graphs

  • Important to recognize variations and make necessary adjustments

  • Performance often based on:

    • Standard atmospheric conditions

    • Pressure altitude

    • Density altitude

• Structure of the atmosphere:

  • Mixture of gases: 78% nitrogen, 21% oxygen, 1% other gases

  • Contains mass and weight, capable of flowing and changing shape

11-3 Atmospheric Pressure Effects on Performance

• Atmospheric pressure influences:

  • Weather changes

  • Aircraft lift

  • Flight instruments (e.g., altimeter, airspeed indicator)

• Effects of air density on performance:

  • Reduced power and thrust as air density decreases

  • Lift diminishes with less dense air

• Standard temperature lapse rate:

  • Decreases by approximately 3.5°F or 2°C per 1,000 ft to 36,000 ft

  • Causes variation in aircraft performance

  • Adjustments for nonstandard conditions provided in performance charts

11-4 Pressure and Density Altitude

• Pressure Altitude:

  • Height above standard datum plane (SDP)

  • Influences aircraft performance and flight levels above 18,000 ft

• Pressure altitude determination methods:

  1. Set altimeter to 29.92 inHg

  2. Apply correction for reported altimeter setting

  3. Using a flight computer

• Density Altitude:

  • Indicates aircraft performance in nonstandard atmospheric conditions

  • Higher density altitude decreases performance

  • Corresponds to standard atmosphere for specific values of air density

11-5 Effects of Density Variations

• Density affected by:

  • Altitude

  • Temperature

  • Humidity

• Density altitude increases due to:

  • High elevations

  • Low atmospheric pressure

  • High temperatures

  • High humidity

• Importance of calculating density altitude to predict performance:

  • Higher density altitude results in increased ground roll distance in takeoff conditions

11-6 Standard Atmospheric Conditions

• Atmospheric density directly related to pressure:

  • Higher pressure increases density, and lower pressure decreases it (constant temperature)

• Effects of temperature on density:

  • Increased temperature decreases density (constant pressure)

• Humidity's impact on density:

  • Moist air is lighter than dry air; thus, increases in humidity lower density altitude and consequently decrease performance

11-7 Performance Characteristics

• Performance Defined:

  • Ability of an aircraft to achieve key functionalities: short distances for takeoff/landing, heavy loads, high speeds, and long ranges

• Major affected factors:

  • Takeoff and landing distances, rate of climb, ceiling, payload, range, speed, maneuverability, stability, fuel economy

• Balancing conflicting performance requirements is crucial in aircraft design

11-8 Straight-and-Level Flight

• Conditions for steady, level flight:

  • Lift must equal weight

  • Powerbank thrust must equal aircraft drag

• Different types of drag:

  • Induced drag vs parasite drag based on conditions of flight

  • The drag-to-thrust ratio informs overall performance in flight

11-9 Climb Performance

• Factors contributing to climb performance:

  1. Using excess power above required level flight conditions

  2. Converting airspeed to altitude

• Importance of VY (best rate of climb) and VX (best angle of climb)

• Excess thrust needed for steep climbs aids in avoiding obstacles

11-10 Takeoff and Landing Performance

• Variables influencing takeoff and landing:

  • Conditions such as gross weight, pressure altitude, temperature, and wind speed.

• Runway surface and gradient affect takeoff and landing performance

• Significance of pilot decisions during critical phases of flight

11-11 Performance Speeds and Charts

• Importance of performance charts:

  • Predicting takeoff, climb, cruise, and landing performance

  • Collecting relevant performance data for safe flight planning

• Various speeds to monitor:

  • True airspeed (TAS), indicated airspeed (IAS), calibrated airspeed (CAS), equivalent airspeed (EAS)

• Understanding how to work with charts in practical situations is crucial for safe operations.