Airplane Performance Charts

Private Pilot License (PPL) Notes

This section introduces key concepts of airplane performance charts and their importance for pilots in understanding aircraft capabilities and limitations under various conditions.

Understanding Airplane Performance:

1. Definition of Airplane Performance:
   1. The capability of an airplane to operate effectively while serving a specific purpose.
2. Elements of Performance:
   1. Takeoff and landing distances.
   2. Rate of climb and ceiling.
   3. Speed and maneuverability.
   4. Stability, payload, and fuel economy.
3. Performance Trade-offs:
   1. Some elements may be mutually exclusive (e.g., high speed vs. short landing distance).
   2. Design differences reflect specific performance goals.
4. Examples of Airplane Designs:
   1. Agricultural airplanes: high payload, low speed, short takeoff and landing distances.
   2. Turbojet airplanes: sleek design, high cruise speed, longer takeoff and landing distances.

Atmospheric Density and Its Impact:

1. Importance of Atmospheric Density:
   1. Airplanes perform better in dense air.
   2. Performance degrades in less dense air.
2. Factors Affecting Density:
   1. Pressure: Higher pressure increases density.
   2. Temperature: Lower temperatures increase density.
   3. Humidity: Lower humidity increases density.
3. Effects of Low Density:
   1. Reduced engine power.
   2. Decreased propeller efficiency.
   3. Reduced lift from the wings.

Understanding Density Altitude:

1. Definition:
   1. Density altitude is pressure altitude corrected for non-standard temperature.
   2. Reflects aircraft performance under current atmospheric conditions.
2. Calculating Density Altitude:
   1. Use a density altitude chart or an E6B flight computer.
   2. Requires pressure altitude and temperature data.
3. Determining Pressure Altitude:
   1. Set altimeter to 29.92 inches Hg and read indicated altitude.
   2. Use indicated altitude and altimeter setting with a conversion table if no altimeter is available.
4. Example Calculations:
   1. Altimeter Setting 30.30 inches Hg:
      1. Subtract 348 feet from indicated altitude to find pressure altitude.
      2. Example: Indicated altitude of 2,000 feet results in pressure altitude of 1,652 feet.
   2. Altimeter Setting 30.35 inches Hg:
      1. Interpolate between values for precise correction.
      2. Adjust indicated altitude accordingly.
5. Using Density Altitude Charts:
   1. Familiarize yourself with the chart before use.
   2. Axes:
      1. Horizontal: Temperature (°F and °C).
      2. Vertical: Density altitude.
   3. Pressure altitude lines slope upwards from left to right.
   4. Standard temperature lines may slope downwards.
   5. Example: Finding density altitude for 3,500 feet pressure altitude at 95°F:
      1. Enter chart at 95°F, move up to halfway between 3,000 and 4,000-foot pressure altitude lines.
      2. Move horizontally to read density altitude of approximately 6,500 feet.

Using Performance Charts and Tables:

1. Acquaint Yourself with the Chart:
   1. Review sample problems provided.
   2. Understand how to navigate the chart or table.
2. Types of Charts:
   1. Stall speed vs. weight, flap setting, and angle of bank.
   2. Density altitude charts.
   3. Manufacturer-specific performance data.
3. Interpreting Stall Speed Charts:
   1. Left-hand section: Airplane weight.
   2. Dot-dash lines: Calibrated airspeed at stall.
   3. Solid lines: Indicated airspeed at stall.
   4. Flap settings at 0° and 40°.
   5. Right-hand side: Bank angle adjustments.
4. Observations on Stall Speed:
   1. Flaps extended to 40° lower stall speed.
   2. Increasing weight or bank angle raises stall speed.
5. Example Problem Solving:
   1. Find indicated stall speed at 2,325 lbs, 0° flaps, 30° bank:
      1. Begin at maximum weight line up to 0° flaps curve.
      2. Move straight over to 0° bank angle.
      3. Guide along up-sloping lines to 30° bank.
      4. Read indicated stall speed of 54 knots.

Understanding Performance Tables:

1. Cessna's Tabular Data:
   1. Stall speeds are presented in tables instead of graphs.
   2. Lists speeds for specific conditions:
   3. Most rearward and most forward center of gravity (C.G.).
2. Advantages and Limitations:
   1. Ease of use for listed conditions.
   2. Limited to specific variables; interpolation may be required.
   3. Some variables (e.g., angle of bank) cannot be interpolated.
3. Example with Cessna 172:
   1. At 2,550 lbs and 0° bank:
      1. Indicated stall speed with most rearward C.G.: 48 knots.
   2. At 30° bank:
      2. Increased load factor raises stall speed to 52 knots.

Understanding and effectively using airplane performance charts and tables are essential skills for safe and efficient flight operations. Always consult the Pilot's Operating Handbook for your specific aircraft to obtain accurate performance data.