Taking Flight: The Art and Science of Airplane Design

Planes are perhaps the most marvelous engineering invention of the modern age. The ability to transport hundreds of people across vast distances at high altitudes is a testament to the incredible progress in aerospace engineering. From the days of riding on camels to the era of global air travel, human civilization has undergone a remarkable transformation enabled by advancements in flight technology. In this article, we will explore the design considerations of an airplane.   
 
As a generation born in the era where airplanes existed long before us, we may sometimes fail to appreciate the sheer marvel of these engineering achievements. Did you know that over 130,000 flights are taken per day, with roughly 6 million people traveling by air around the world? 

Understanding Aerodynamics ​

The design of airplanes is a complex and fascinating field worthy of exploration. Aerospace design is driven by aerodynamics which is a field that allows us to understand how an object (airplane) moves through air by studying the forces acting on the object (airplane). It is what enables us to understand the different forces acting on the airplane, whether an airplane will fly, and how the design of an airplane can be optimized such that it can fly the furthest and the fastest. 

Forces on an Airplane

​Before getting more into the design, let us understand the fundamentals of how an airplane works. In flight, an airplane is being acted on by four forces: lift, drag, weight, and thrust which are shown below. 

​Figure 1: Aerodynamic forces on an airplane

Let us summarize each force as follows:
 

• Lift: Upwards force generated through Bernoulli’s theorem
• Drag: Backwards force created mainly due to the interaction between the plane’s surface and the air
• Weight: Downward force due to the mass of the plane
• Thrust: Forwards force generated by the engine

 
Among these four forces, there are two desirable forces and two undesirable forces. Can you guess which is which? Think of which forces speeds up the plane and which slows down the plane.
 
Drag (backwards force) and weight (downwards force) slows down an airplane and bring it down and are hence undesirable. Airplanes are thus strategically designed to minimize drag and weight. Whereas lift (upwards force) and thrust (forwards force) are desirable since they propel and enable airplanes to fly. Thus, the airplane is strategically designed to optimize lift and the engines are designed to generate maximum thrust.
 

The Core Elements of an Airplane ​

An airplane can be broken into several parts where each part is designed as aerodynamically efficient as possible. The core parts of an airplane are the fuselage, wings, tails, landing gears and nacelle which are shown below. 

​Figure 2: Airplane

The fuselage, which is the circular tube-like structure, can be considered as the body of an airplane. It is what houses the passengers and the wings. Fuselages are circular in shape not due to aesthetics, but rather for aerodynamic reasons. The smooth rounded surface reduces air resistance and offers lower drag compared to other shapes, proving to be more aerodynamically efficient. It also distributes the internal and external forces evenly to reduce stress concentrations. 

Generation of Lift by the Wings ​

​Moving on to the wing, which is the heart of an airplane, as it provides most of the lift generated by the airplane. Below is a cross-section of a wing called an airfoil. 

​Figure 3: Airfoil

Airfoils are used to manipulate the movement or reaction of the air when the airplane passes through the air. For an airplane, an airfoil is what enables heavier-than-air flight due to the generation of lift.
 
Airfoils are strategically designed such that the top surface of the airfoil has a greater curvature than the lower surface. Physics plays a huge role here. Due to the increased curvature of the upper surface, as the air flows over the airfoil, it speeds up. As the speed increases above the airfoil, the pressure decreases as per Bernoulli’s principle. Hence, a net upward force (lift) is created as the pressure above the airfoil is lower than the pressure below the airfoil.

Taking Inspiration from Nature  ​

Some airplanes, such as the widely known and loved A380, have winglets, which are extensions of the wingtips that as shown below. 

Figure 4: Winglets

They are used to reduce drag to improve the aerodynamic efficiency of the wing. The inventor of winglets took inspiration from nature, specifically the shape of bird’s wing. Some birds such as eagles, as shown in the picture below, have upturned tips which helps to reduce drag during flying. After studying the effect of these upturned tips in wind tunnels, engineers developed winglets for planes to mimic the upturned tips of the birds to improve the aerodynamics of the wings.

​Figure 5: Wings of an eagle 

​The Importance of Retracting the Landing Gear 

Another crucial aerodynamic design feature is the retraction of landing gear upon take-off. The landing gear is retracted to reduce drag. Since every exposed part on the airplane is subject to drag, engineers aim to reduce the number of exposed parts of the airplane. A way to achieve this is to retract the landing gears upon take-off as they are not used during cruise. 

Evolution of Airplane Windows 

The design of airplanes is everchanging. In fact, the windows of airplanes were not always the oval windows we see today. The world’s first commercial jetliner, de Havilland Comet, had great success upon entering the market in the 1950’s. However, it soon faced two fatal crashes which resulted in a loss of 56 lives. The culprit for the crashes was found to be the square windows, which lead to stress concentrations at the corners and hence resulted in structural weaknesses in the fuselage. This prompted de Havilland to modify the design of the windows, and soon later, oval windows were introduced to ensure even distribution of stress. These oval windows are still used today many years later, and have proven to be a safe and effective design. 

​Figure 6: Oval windows

Conclusion 

The design of airplanes is a result of a complex interplay between aerodynamics, structural engineering, materials science, avionics, human factors, regulatory requirements, and a continuous drive for innovation and improvement in aviation technology. So, the next time you fly, remember to take a minute to appreciate all the hard work that go behind designing an airplane. From the streamlined fuselage to the ingenious wing design, each component represents the culmination of decades of research, experimentation, and innovation in the field of aerospace engineering. 

Image Credits:
Picture credit of airfoil is to Wikipedia Commons.
All other images are taken from freepik.

By Iqra Bibi
Iqra is an aerospace engineering student at HKUST. She is interested in the world of aviation and beyond. She is passionate bringing a change and being a part of a community that strives for the betterment of the society.