With aircraft being as popular as they are, and with governments and private corporations dedicating millions of dollars every year to aviation development, it is worth asking: Why fly?
An informative study to help answer this question is “What Price Speed?” a research paper written by the aerodynamicists Theodore von Kármán and Giuseppe Gabrielli in 1950. In their paper, they first defined a quantity called the “specific tractive force” of a vehicle. It can be thought of as a cost of operation. Vehicles with higher specific tractive forces require more energy to operate. From there, they plotted specific tractive force against speed for commercial planes, jet fighters, ocean liners, cars, trains, and even some animals. Upon examining this graph, it is clear that while aircraft have higher than average specific tractive forces, they can travel at nearly unparalleled speeds. To quantify this observation, many commercial jets travel between 200-500 km/hr, while most automobiles and diesel-electric trains travel at closer to 100 km/hr, and ocean liners lumber along at 40 km/hr. With this speed, a three-thousand-mile trip across the United States can be reduced from multiple days to six hours.
Airplanes are also more fuel-efficient than alternative transportation methods. This might not immediately be obvious. After all, a large airliner consumes orders of magnitude more fuel than an individual car in a period of three to four hours. However, the superior fuel efficiency of aircraft can become clear by considering liters of fuel consumed per 100 km per passenger. Indeed, the Boeing 737 MAX passenger jet consumes just 2L/100km/passenger, while the Toyota Prius consumes 4L/100km/passenger and the now-retired RMS Queen Elizabeth II ocean liner consumed 17L/100km/passenger.
While there certainly are vehicles that consume less fuel per 100 km per passenger than aircraft, there are even more reasons to fly than just speed or fuel efficiency. Planes can easily fly on their own (without any tunnels, bridges, or other extra infrastructure) over vast oceans and mountain ranges, serve as observation platforms for reconnaissance, or collect scientific data at high altitudes and high speeds.
With so many reasons for flying, it then makes sense that engineers have continued to push the boundaries of aviation technology.