Symmetrical airfoil

Definition

A symmetrical airfoil is a type of airfoil that has identical upper and lower surfaces, which means it has no camber. This characteristic allows for equal lift generation on both sides at zero angle of attack, making it particularly useful in applications where performance is required in both upward and downward motions. Symmetrical airfoils are essential in understanding the fundamental principles of airfoil geometry and play a significant role in thin airfoil theory, especially in predicting lift and drag characteristics across various flight conditions.

5 Must Know Facts For Your Next Test

1. Symmetrical airfoils produce lift at zero angle of attack, unlike cambered airfoils which require a positive angle to generate lift.
2. They are often used in control surfaces such as ailerons and elevators because their symmetrical nature allows for predictable performance in both directions.
3. In thin airfoil theory, symmetrical airfoils can be analyzed using mathematical models that simplify calculations for lift and drag.
4. The lack of camber in symmetrical airfoils means they typically have a lower maximum lift coefficient compared to cambered designs.
5. Symmetrical airfoils can be more efficient at high speeds due to reduced drag when compared to cambered counterparts under certain conditions.

Review Questions

• How does the symmetry of an airfoil influence its performance at different angles of attack?
  • The symmetry of an airfoil allows it to generate equal lift on both its upper and lower surfaces at zero angle of attack. This means that as the angle of attack increases, the lift produced can change uniformly on either side, which is crucial for control surfaces like ailerons. In contrast, cambered airfoils may only generate significant lift above a certain angle, highlighting the importance of symmetry for applications requiring consistent performance across various flight conditions.
• Discuss how symmetrical airfoils are utilized in control surfaces and their impact on aircraft stability.
  • Symmetrical airfoils are commonly used in control surfaces like ailerons and elevators because their design allows for balanced control responses regardless of the direction the aircraft is moving. This balanced nature helps pilots maintain stability during maneuvers since these surfaces can provide predictable lift characteristics whether moving up or down. Such performance is critical for ensuring smooth handling qualities and reducing the likelihood of adverse yaw during turns.
• Evaluate the advantages and disadvantages of using symmetrical airfoils compared to cambered airfoils in various flight scenarios.
  • Using symmetrical airfoils offers several advantages, including consistent lift generation at zero angle of attack and predictable behavior in both upward and downward movements. This makes them ideal for certain control surfaces where responsiveness is key. However, they typically exhibit lower maximum lift coefficients compared to cambered airfoils, which excel at generating lift at low angles but may stall more easily. Therefore, while symmetrical designs are excellent for specific applications, cambered designs often provide better overall performance in scenarios demanding high lift at low speeds.

Related terms

Camber: The curvature of an airfoil that affects its lift characteristics, with positive camber producing more lift at lower angles of attack.

Angle of Attack: The angle between the chord line of the airfoil and the direction of the oncoming airflow, crucial for determining lift generation.

Lift Coefficient: A dimensionless number that relates the lift generated by an airfoil to the dynamic pressure and reference area, helping to characterize its performance.