<< Page 22 Page 23: Page 24 >>   Airplane Design Features This is the fun part. We will apply the knowledge of control, stability and aerodynamic forces to figure out why airplanes are designed the way they are. We will review the reasons behind some features we have already talked about, and understand the reasons behind other features. We will see how looking at the features of an unknown airplane will tell us a lot about that airplane’s performance, purpose, age and efficiency. For example, I have already mentioned that swept wings generate less drag at supersonic speeds, that high-aspect-ratio wings generate less induced drag especially at low speeds, that engines that are low and near the nose are good for stability, that flaps and slats increase lift (by increasing camber and cord), that turbulent boundary layers increase viscous drag but delay separation… Let’s talk more about such design choices, so as to understand why airplanes have the features they do, and why they are so different.