4.2 Directional Innovation in Aircraft
Marcos Antonio de Lima Filho, PhD.
The pioneering turboprops and turbojets of the jet era were highly disruptive, both in technological and market domains. The jet era marks the introduction of a new architecture for engine propulsion, with a considerable impact on market structure. Due to its impact on how an aircraft flies, jet propulsion required a fundamental revision of previous aircraft designs.
Following this highly disruptive phase, the aviation industry has shifted its focus to a path of continuous and cumulative improvement. To this date, we are still flying on jets, but thanks to decades of incremental innovation, passengers can now enjoy cheaper, cleaner, safer, and longer flights.
The popular press often portrays disruptive innovation as a heroic entity, sometimes apocalyptic. Despite that, the data presented here shows an important but overlooked role played by incremental and cumulative changes. The dynamic nature of innovation also highlights the necessity of understanding disruptive innovation in tandem with other “modes” of innovation.
The following charts illustrate major technological trends in operation since the jet era. From the 1960s onwards, commercial aircraft have developed towards greater engine efficiency (Figures 4.2.1, 4.2.2, and 4.2.3), improved aerodynamics (Figure 4.2.4), and increased performance (Figure 4.2.5). In sum, decades of incremental advancements have enabled planes to fly with reduced fuel consumption, decreased aerodynamic drag (which further enhances efficiency), more passengers, and longer distances.
To trace the historical evolution of aircraft performance, I utilised production data to calculate the annual average performance of newly delivered aircraft. This involved summing the specified performance of each aircraft delivered within a given year and dividing this total by the number of aircraft delivered during that period. This calculation can be applied to all aircraft, as demonstrated in Figure 4.2.1, or to specific categories such as narrow-bodies, regional jets, and wide-bodies. Most spreadsheet software (including Microsoft Excel, Google Sheets, and Apple Pages) can be employed to carry out this simple analysis. By creating a pivot table, the large dataset of aircraft registries can be narrowed down to its basic trends with just a few clicks. With the pivoted results in tabular form, charts can be generated to visually represent the incremental evolution of aircraft performance across the years.
Fuel Efficiency
Fuel efficiency can be an excellent indicator of the evolution of airliners because several dimensions can have an impact on this measure. Aerodynamic improvements, weight reduction, and the use of more efficient engines are ways in which manufacturers can improve efficiency. Airline operators contribute by managing their fleet for optimal passenger loads and by flying at optimum altitudes and airspeeds. All of these parameters are carefully calibrated because fuel is one of the most expensive components of an airline operation. Consequently, when an airline decides to buy new equipment, fuel consumption is one of the first things it looks at; there is also a direct link between reduced fuel use and environmental performance (ATAG, 2010).
Engines
Aircraft engines can be subdivided into four main groups. These are very short explanations, but the internet abounds with videos and articles that better illustrate these technologies:
Piston Engines (1930s—1960): Piston engines were the first propulsion technology to power commercial passenger aircraft. The internal combustion inside the cylinders moves a number of pistons and a shaft. The piston converts chemical energy (fuel) into rotational power that drives a propeller.
Turbojet Engines (1950–1960): Turbojets have neither pistons nor cylinders. Thrust is produced by increasing the velocity of the air flowing through the engine (Federal Aviation Administration, 2016, 7-20). Instead of relying on moving parts, the turbojet produces thrust by controlling the ignition of the fuel-air mixture.
Turboprop Jet Engines (1950—today): The propeller is driven by a turbojet core attached at the back.
Turbofan Jet Engines (The late 1950s—today): Unlike a turbojet that funnels all air into its engine core, a turbofan is equipped with a large fan at the forefront of its jet engine core. This configuration allows most of the airflow to be guided around the hot core, thereby creating additional thrust and establishing a bypass ratio.
Engine bypass ratio is a primary metric of turbofan evolution. Turbofan engines produce extra thrust by directing a secondary air stream around the combustion chamber. This bypass air not only boosts thrust but also cools the engine and helps reduce exhaust noise, ensuring cruise speeds comparable to turbojets and more economical fuel consumption.
As the bypass ratio increases, fuel consumption typically improves since more thrust is generated without burning extra fuel (ATAG, 2010). The bypass ratio refers to the ratio of the mass airflow that passes through the fan divided by the mass airflow that passes through the engine core (Federal Aviation Administration, 2016, 7-21). That is, if there is twice as much cold air bypassing the core as the hot air going through it, the bypass ratio is 2:1 (ATAG, 2010).
Since the early 1960s, the aviation industry has favoured the efficiency gains brought by turbofans. Figure 4.2.2 shows a steady increase in the yearly average turbofan bypass ratio across all turbofan aircraft classes.
Advancements in high-bypass engines have resulted in a rise in maximum thrust and larger turbofans (Figure 4.2.3). The latest turbofan engines feature bypass ratios of 10 to 12.5. Notably, the most advanced wide-body aircraft engines generate over 115,000 pounds of thrust each, outperforming the combined thrust of four engines from the late 1960s while using less fuel, emitting fewer emissions, and producing a smaller noise footprint (ATAG, 2010).
As bypass ratios increase, engine diameters must also expand to accommodate larger fans (Figure 4.2.3). The development of larger and more powerful engines has enabled manufacturers to develop wide-body aircraft with dual-engine setups, thereby causing the obsolescence of tri- and quad-turbofan aircraft.
Aerodynamics
Aircraft flight performance is governed by aerodynamics, structures, and engines; all other specific disciplines, although often important for the viability of an aircraft, are only weakly related to the flight performance of transport aircraft (Sobieczky, 2014, p. 32). The increasing wingspans and wing aspect ratios of current passenger aircraft reflect advances in aerodynamics.
Wingspan refers to the overall length of a wing. The ratio of the overall wingspan (length) to the average chord (width) is known as the aspect ratio (Barnard & Philpott, 2010, p. 37). Higher wing aspect ratios are a technical challenge. The early pioneers noted that the wings of birds always have a much greater span than chord; Simple experiments confirmed that high aspect ratio wings produced a better ratio of lift to drag than short stubby ones for flight at subsonic speeds (Barnard & Philpott, 2010, p. 37).
Other things being equal, an increase in aspect ratio will decrease drag, thus improving the wing’s and the aircraft’s aerodynamic performance. It should be noted, however:
(…) with an increase in aspect ratio there is an increase in the length of span, with a corresponding increase in the weight of the wing structure, which means the wing must be heavier to carry the same load. For this reason, part of the gain (due to a decrease in drag) is lost because of the increased weight, and a compromise in design is necessary to obtain the best results from these two conflicting conditions (Federal Aviation Administration, 2016, p. 5-21).
That is, as the aspect ratio of the wing increases, maintaining its strength and stiffness becomes more challenging. This relationship is an example of an evolutionary trade-off, which occurs when “increasing fitness in one way decreases it in another” (Futuyma & Kirkpatrick, 2017, p. 152).
Performance
Passenger airliners are flying more passengers to longer distances (see Figure 4.2.5). These technological improvements have changed how the air travel industry operates. Previously, operators consolidated traffic into large aircraft (wide-body four-turbofan). Nowadays, passengers want the convenience of flying point-to-point. Smaller long-haul aircraft (such as the A330neo, A350, 777, 787, 777X, and the A321XLR) are the best fit for these missions, with excellent economic performance.
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