Lift and Drag Variations

Introduction

Understanding the factors affecting lift and drag on an aerofoil is crucial for safe and efficient flight operations. This section will cover how changes in airspeed, angle of attack, and flap settings influence lift and drag on an aerofoil, providing pilots with foundational knowledge for flight control and performance optimization.

Effects of Airspeed on Lift and Drag

Airspeed and Lift

Bernoulli’s Principle: As airspeed increases, dynamic pressure on the aerofoil increases, leading to reduced static pressure and subsequently increased lift (Introduction to the Aerodynamics of Flight - Theodore A. Talay).
Coefficient of Lift (Cl): Lift generally increases with airspeed due to higher dynamic pressure acting on the wing surfaces, assuming the angle of attack remains constant.

Airspeed and Drag

Total Drag Components: Comprises parasitic drag (form, skin friction) and induced drag. Parasitic drag increases with airspeed due to higher flow velocity over the aerofoil surfaces.
Induced Drag Hypothesis: At lower speeds, induced drag (linked to lift generation) is significant but decreases as speed increases and becomes less dominant compared to parasitic drag at higher speeds.

Effects of Angle of Attack on Lift and Drag

Angle of Attack and Lift

Low AoA: Produces a moderate amount of lift with minimal drag.
Increasing AoA: Lift increases with an increase in angle of attack up to the critical angle. Beyond this point, lift decreases due to airflow separation and stall (Checklist: Angle Of Attack Knowledge And Awareness - Aviation Week).

Angle of Attack and Drag

Increased AoA: Leads to increased drag due to larger airflow separation over the wing surfaces.
Critical AoA: Beyond this angle, drag increases significantly as a consequence of stalled airflow and increased pressure drag.

Effects of Flap Settings on Lift and Drag

Flap Settings and Lift

Increased Camber: Deploying flaps increases the camber of the wing, enhancing the lift coefficient, allowing for more lift at a given angle of attack (5 Aerodynamic Facts Pilots Should Know About Flaps - Boldmethod).

Flap Settings and Drag

Induced Drag: As lift increases with flap deployment, so does induced drag. This additional drag helps control descent rates, especially during landing phases.
Operational Considerations:
- Takeoff: Flaps set typically between 5-15 degrees to balance increased lift with manageable drag.
- Landing: Greater flap extension maximizes both lift and drag, allowing for slower, controlled approaches (Airplane Flying Handbook (3C) Chapter 5 - Federal Aviation Administration).

Conclusion

Pilots must understand how changes in airspeed, angle of attack, and flap settings influence lift and drag on an aerofoil to ensure efficient and safe flight operations. Mastery of these concepts helps in optimizing aircraft performance and managing flight conditions effectively, particularly during critical phases such as takeoff and landing.