FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightMedium
A technician installs vortex generators, small vane-like devices, along the upper wing surface of a light airplane under an STC modification. What is their primary aerodynamic purpose?
- ATo reduce induced drag by weakening the strength of wingtip vortices
- BTo reduce parasite drag at high cruise airspeeds by smoothing airflow
- CTo increase the wing's effective aspect ratio for better climb performance
- DTo re-energize the boundary layer airflow, delaying separation and increasing the wing's stall angle of attack
Show answer & explanationAnswer & explanation
Correct answer: D. To re-energize the boundary layer airflow, delaying separation and increasing the wing's stall angle of attack
Vortex generators create small, controlled vortices that mix high-energy air from outside the boundary layer into the slower-moving air near the wing surface, re-energizing the boundary layer and delaying flow separation, which allows the wing to reach a higher angle of attack before stalling.
Why the other options are wrong
- A. Wrong — vortex generators address boundary layer separation, not wingtip vortices
- B. Wrong — they slightly increase parasite drag rather than reduce it, especially at cruise
- C. Wrong — they do not change the wing's geometric or effective aspect ratio
Vortex Generators
Small vane-like devices mounted on the upper wing surface that create controlled vortices to re-energize the boundary layer, delaying flow separation and increasing the stall angle of attack.
- Mix high-energy outer airflow into the slower boundary layer
- Slightly increase parasite drag at cruise speeds
- Often used to lower stall speed or improve control effectiveness at high AOA
Memory trick: Vortex generators are tiny blenders stirring fresh energy into a tired boundary layer