4.3 Stabilising Innovation in Aircraft

Marcos Antonio de Lima Filho, PhD.

Evolution cannot occur without change, yet not all changes prove to be beneficial. Natural selection is constantly balancing change with a certain degree of conservatism, preserving what is currently optimal while adapting where necessary.

The first Ford Model T was introduced in 1909. Today, after more than a century, we continue to ride on four wheels with rubber tyres. Cars have evolved significantly, yet many design elements that emerged during these blooming years can still be found today. Design evolution is, thus, a balancing process that stabilises what is currently optimal while other parts evolve in a disruptive or incremental way.

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Maximum Operating Speed

Several configurations and performance metrics of commercial aircraft have stabilised over the last 50 years. This has less to do with monopolistic competition (that usually stifles innovation), or an incompetence to innovate. Such stabilisation is more likely the result of the laws of thermodynamics, aerodynamics, and operating economics. Maximum Operating Speed (Figure 4.3.1), for example, has stabilised since the dawn of the jet era. It is still possible to fly faster without breaking the sound barrier (1,200 km/h), but doing so brings diminishing returns in terms of fuel consumption. Almost all aircraft today are equipped with a Flight Management System that automatically calculates the most fuel-efficient cruising speed, taking into account the route, aircraft weight, and external weather.

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Flying Altitude & Pressurisation

Pressurisation was first successfully introduced to passenger flights on the Boeing 307 Stratoliner in 1938 (Gudmundsson, 2013). Since then, this feature has become a de facto standard in all commercial aircraft. Flying altitude has also stabilised at about 41,000 feet for turbojets, and at 25,000 feet for turboprops (Figure 8.4.1 - 8.4 The Stabilisation of Qualitative and Quantitative Traits). Higher altitudes have lower air resistance, thus lowering fuel consumption. However, turbofan engines cannot produce enough thrust above a certain level. The same applies to turboprops: with too little air resistance, the blades can no longer produce enough thrust. Section 5.3 discusses the stabilisation of other features, such as retractable landing gears and the “tube and wing” architecture.