Aerodynamics & Performance
Aerodynamics is the branch of dynamics dealing with the motion of air and other gases that provide the performance aircraft need to fly.
Introduction to Aerodynamics & Performance
- Aerodynamics is the branch of dynamics dealing with the motion of air and other gases, which gives us the performance we need to fly.
- Every flight is influenced by the relationship between the aircraft, the atmosphere, and the pilot's decisions.
- It begins with understanding why an airplane flies, continues with recognizing how aerodynamic forces influence aircraft behavior, and eventually leads to applying that knowledge during flight planning.
- Along the way, pilots must also consider how the atmosphere changes aircraft performance and learn to interpret performance information before and during every flight.
- Understanding why an airplane flies, how it responds to changing conditions, and what limits its performance helps pilots make informed decisions long before advancing the throttle or leaving the runway.
Understanding How Aircraft Fly
- Before applying performance calculations or evaluating aircraft limitations, it helps to understand the principles that make flight possible.
- Aircraft components and structure create the physical form we know as an aircraft.
- Principles of flight explains how four opposing forces interact to produce controlled flight and influence every maneuver. []
- Thrust: is the forward force produced by the powerplant/propeller, overcoming the force of drag.
- Drag is a rearward, retarding force caused by the disruption of airflow by the wing, fuselage, and other protruding objects as well as the creation of lift.
- Lift opposes the downward force of weight, produced by the dynamic effect of the air acting on the wing.
- Weight is the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage which pulls the aircraft downward because of the force of gravity.
- The interaction of these principles guides engineers in designing aircraft with different handling characteristics to achieve the desired stability along their three axes. []
- The longitudinal, or roll, axis extends through the aircraft from nose to tail, with the line passing through the center of gravity.
- The lateral or pitch axis extends across the aircraft on a line through the wing tips, again passing through the center of gravity.
- The vertical, or yaw, axis passes through the aircraft vertically, intersecting the center of gravity.
- All control movements cause the aircraft to move around one or more of these axes, enabling control of the aircraft in flight.
- Before every flight, pilots verify that the aircraft is loaded within its approved limits because weight and balance directly affects stability, controllability, and performance.
Understanding Aerodynamic Performance
- An airplane is constantly responding to changes in airspeed, angle of attack, configuration, and control inputs.
- Stalls are an aerodynamic condition whereby air can no longer smoothly flow over an airfoil due to the surface exceeding its "critical" angle of attack, resulting in a rapid loss of lift.
- Although angle of attack is an abstract concept expressed in abstract units, several stall speed considerations are taken into account in aircraft design and performance envelopes to ensure the aircraft remains within the standard flight envelope.
- As bank angle increases or the airplane is maneuvered more aggressively, understanding turn performance helps pilots recognize how lift, load factor, rate of turn, and radius of turn are related.
- The interaction of these concepts allow pilots to maximize aircraft performance and minimize risk.
- Coordinated control inputs become more important as maneuvering demands increase because the airplane's aerodynamic forces are no longer acting only in straight-and-level flight.
- Stalls are an aerodynamic condition whereby air can no longer smoothly flow over an airfoil due to the surface exceeding its "critical" angle of attack, resulting in a rapid loss of lift.
Applying Performance to Flight Planning
- The performance or operational information section of the Aircraft Flight Manual/Pilot's Operating Handbook (AFM/POH) contains the aircraft's takeoff, climb, range, endurance, descent, and landing data. [/]
- Using this data in flying operations is mandatory for safe and efficient operation.
- Aerodynamic knowledge becomes practical when pilots begin planning a flight.
- Sufficient takeoff and climb performance is required to safely transition an aircraft from the terminal to enroute structure.
- Before departure, pilots therefore consider takeoff and climb performance to determine whether the aircraft can safely depart, clear obstacles, and continue climbing under existing conditions.
- During cruise, pilots balance power, fuel consumption, range, endurance, to efficiently achieve desired cruise performance.
- By appreciating the various factors that impact cruise performance, pilots directly influence the duration and quality of a flight for their passengers, themselves, and their wallet (gas, wear, etc.).
- Pilots must also consider glide performance to understand aircraft energy, engine-out options, and how far the airplane may travel without power.
- As the flight nears the destination, pilots execute procedures to achieve the appropriate descent and landing performance.
- Starting with the descent, pilots establish safe, deliberate, and predictable profiles to establish a stabilized approach to land on suitable surfaces.
Recognizing the Effects of the Environment
- Aircraft performance is never constant because the atmosphere is always changing. []
- As pilots gain experience, they quickly learn that an airplane rarely performs the same way twice.
- The effects of atmospheric conditions explain how changes in pressure, temperature, altitude, and air density influence aircraft capability.
- Flying in cold weather presents its own set of challenges.
- Cold temperature operations explores how low temperatures affect aircraft performance, aircraft systems, and operational decision-making.
- Warm weather can have an equally significant impact on aircraft performance.
- Warm temperature operations explains why high temperatures and density altitude reduce takeoff, climb, and overall aircraft capability.
- Atmospheric conditions can also create psychological and physiological effects that affect pilots and passengers and, therefore, the quality and safety of the flight operation.
Performance Calculations Versus Reality
- Charts contain performance data based on expected performance under specific conditions.
- In other words, pilot operating handbook numbers necessitate the use of the pilot operating handbook technique.
- The conditions present during calculation will always differ to some degree, and sometimes significantly, from those in the charts and graphs.
- Factors to consider include mechanical, environmental, skill, geographic location, and altitude.
- Performance charts are therefore only useful when pilots understand the assumptions behind them.
- Performance Calculations helps pilots use charts, tables, and aircraft data while recognizing the difference between charted performance and actual performance.
- Manufacturers evaluate aircraft performance under specific conditions and later compile the results into performance charts.
- Pilots must reference these performance charts to calculate the anticipated performance for a given operation.
- Conservative planning matters because aircraft condition, pilot technique, runway surface, wind, temperature, and obstacles can all change the margin available during an actual flight.
- It is essential to recognize that any calculated performance may differ from reality.
- It is important to use conservative numbers.
- Consider always rounding up, rather than interpolating, and using the higher number, etc.
- Realize obstacles like trees may be more than 50'; therefore, charts are wholly inadequate to calculate by numbers.
- Consider adding 50-100% buffers to anything calculated and monitor performance while in flight.
- If numbers were overly conservative, adjust for subsequent flights.
Aerodynamics & Performance Conclusion
- Understanding how these forces are created and, more importantly, how they interact with each other enables pilots to control an aircraft in flight.
- Aerodynamics and performance influence every flight, whether a pilot is loading the aircraft, calculating takeoff distance, maneuvering in the practice area, or preparing to land.
- As you become comfortable with these principles, you will find they support nearly every other area of flight training. Aircraft systems, weather, navigation, flight planning, and regulations all build upon an understanding of how the airplane flies and what it is capable of accomplishing under a given set of conditions.
- Resources like Real Engineering - The Plane That Will Change Travel Forever effectively describe complex aerodynamic topics clearly and concisely.
- Consider actual versus realized performance when doing any performance calculations.
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