Drag Divergence

Definition

Drag divergence refers to the phenomenon where the drag force on an aircraft increases significantly as it approaches transonic speeds, particularly around Mach 0.8 to 1.2. This increase in drag is primarily due to the formation of shock waves and flow separation, leading to a substantial rise in aerodynamic resistance that can affect aircraft performance and stability. Understanding drag divergence is crucial for designing aircraft that operate efficiently across different speed regimes.

5 Must Know Facts For Your Next Test

1. Drag divergence typically occurs around Mach 0.8, where a significant increase in drag can be observed as airflow begins to compress and form shock waves.
2. The sudden rise in drag during drag divergence can impact fuel efficiency, maneuverability, and overall performance of the aircraft.
3. Aircraft designs often include features like supercritical airfoils to delay drag divergence and enhance performance in transonic flight regimes.
4. Flow separation due to drag divergence can lead to control issues, causing an aircraft to experience instability at high speeds.
5. Understanding and predicting drag divergence is essential for engineers when conducting flight tests and developing high-speed aircraft.

Review Questions

• What are the effects of drag divergence on aircraft performance during transonic flight?
  • Drag divergence leads to a significant increase in aerodynamic drag as an aircraft approaches transonic speeds, which can adversely affect its performance. This increase in drag can reduce fuel efficiency and limit the aircraft's maximum achievable speed. Furthermore, it may cause flow separation, resulting in control difficulties and potential instability during flight. Pilots must be aware of these effects to manage their aircraft effectively in this critical speed range.
• How do shock waves contribute to the phenomenon of drag divergence in transonic flight conditions?
  • Shock waves play a critical role in drag divergence by forming as an aircraft approaches transonic speeds. As airflow compresses around the airfoil and reaches supersonic speeds, these shock waves create sudden changes in pressure and density that dramatically increase drag. The presence of shock waves can also lead to flow separation over the wing, exacerbating the drag increase and leading to further aerodynamic challenges for the aircraft.
• Evaluate how modern aircraft design mitigates the impacts of drag divergence during high-speed flight.
  • Modern aircraft design employs various strategies to mitigate the impacts of drag divergence as they operate at high speeds. Designers utilize advanced airfoil shapes, such as supercritical airfoils, which are specifically crafted to delay shock wave formation and reduce drag at transonic speeds. Additionally, technologies like winglets help manage airflow over wings, reducing flow separation. Computational fluid dynamics (CFD) tools are also leveraged to predict and analyze drag behaviors, allowing engineers to optimize designs for better performance across different flight regimes.

Related terms

Transonic Flow: Transonic flow occurs when an aircraft is traveling at speeds close to the speed of sound, where both subsonic and supersonic flow characteristics are present.

Mach Number: The Mach number is the ratio of the speed of an object to the speed of sound in the surrounding medium, indicating whether the flow is subsonic, transonic, or supersonic.

Shock Wave: A shock wave is a sharp change in pressure and density that occurs when an object travels through a fluid at a speed greater than the speed of sound, often leading to increased drag.