Why aircraft have flaps and how they work ✈️ Airliners are designed to fly efficiently at high speed at high altitudes. To do this, they need sharp, thin wings that can fly at speeds close to the speed of sound. However, wings that are designed to fly efficiently at high speed are not good at flying slowly! Wings that are great at flying slowly are thick, highly cambered (curved) wings - the exact opposite of the efficient, supercritical wings fitted to most airliners! This is big problem! In or