Vortex Generators: Real Bang For the Buck

It’s one of those aircraft truisms that performance requires compromise. Controllability at low speed means compromising the wing that enjoys high-speed cruise. That’s what makes vortex generators (VGs) seem too good to be true: They claim lower stall speeds in singles and twins without a penalty in cruise speed. Sometimes they bump up the gross weight. For twins, they reduce minimum controllable airspeed (Vmc). This is speed below which controlled flight becomes impossible with the critical engine failed and the other engine at full power. Below Vmc, there isn’t enough rudder and aileron authority to counter the natural yaw and roll of the asymmetrical thrust. Translation: The airplane rolls over and crashes.