Small airfoil-shaped devices are installed in rows on the upper wing surface near the leading edge of many transport aircraft, and sometimes on nacelles or the vertical stabilizer. Their primary aerodynamic function is to:
- AEnergize the boundary layer with vortices, delaying airflow separation and extending controllability to a higher angle of attack or Mach number
- BReduce induced drag at cruise by effectively increasing the wing's aspect ratio
- CIncrease directional stability by adding yaw damping alone
- DReduce skin friction drag by streamlining the local airflow
Show answer & explanationAnswer & explanation
Correct answer: A. Energize the boundary layer with vortices, delaying airflow separation and extending controllability to a higher angle of attack or Mach number
Vortex generators are small vanes set at an angle to the local airflow that create small trailing vortices. These vortices mix high-energy air from outside the boundary layer into the slower, energy-depleted air near the surface, delaying flow separation. This extends the usable angle of attack range and improves control effectiveness at high AOA or in regions of shock-induced separation at high Mach.
Why the other options are wrong
- B. Vortex generators do not change wing aspect ratio; that's a wing geometry/winglet function.
- C. Yaw damping is a function of the yaw damper system, not vortex generators.
- D. Vortex generators actually add a small amount of parasite drag; they don't reduce skin friction drag.
Vortex Generators
Small vane-like devices on wings, nacelles, or tail surfaces that create trailing vortices to energize the boundary layer and delay airflow separation, extending controllability at high AOA or Mach.
- Mix high-energy outer air into the boundary layer
- Delay flow separation at high AOA or high Mach
- Add small parasite drag as a trade-off
- Placed on wings, nacelles, and sometimes tail surfaces
Memory trick: VGs stir the pot so the boundary layer doesn't 'go stale' and separate