7.7 Directional Innovation in Commercial Aircraft

Marcos Antonio de Lima Filho, PhD.

Since the Jet Age, to the casual observer, it may appear that commercial aircraft have not changed all that much. They may be larger or have different names, but ultimately, an aircraft is still a big tube with wings on either side; however, this similarity does not do justice to the many factors that go into designing aircraft to operate efficiently (ATAG, 2010, p. 6). As seen in the previous section, incremental improvements have made commercial aircraft up to 72% more efficient than they were in 1960. These gains were accomplished by ongoing advancements in aerodynamics, materials, structures, and propulsion systems.

The innovation focus of this industry is, justifiably so, highly incremental. The industry and its products are inherently exposed to the risk of large-scale catastrophic occurrences, requiring rigorous international and national safety standards and regulations (Spreen, 2020). Because of these risks, aviation is a traditionally very cautious industry, being innovative but also taking a long time to carefully test and certify safety standards for new aircraft (ATAG, 2021).

Furthermore, incremental upgrades tend to favour the economics of key industry stakeholders, such as banks, hedge funds, and aircraft lessors. Nowadays, only a minority of commercial aircraft are purchased in cash by airlines, with the majority being acquired through leasing or financing arrangements. The cost of each aircraft is often in the range of hundreds of millions of dollars, which when multiplied by a fleet, can result in financial demands that are beyond the reach of many airlines (Spreen, 2020). Aircraft leasing has become the preferred method, with lessors now accounting for up to 40% of new orders, and financing about 50% of the aeroplanes operated by airlines (Hamilton, 2021).

The residual value of the aircraft at the completion of the lease has a major impact on the lessor’s profitability (Spreen, 2020). Consequently, actual aircraft owners (leasing and financial institutions) may not benefit from the development of new aircraft derivatives, as new models may result in earlier obsolescence and, therefore, lower residual values.

Manufacturers also prefer incremental innovations that build on existing aircraft in production. Within the industry, a decision to introduce a major new aeroplane is known as “betting the company” because the company is at real risk of failure if the new product fails to sell well enough to recover the investments (Spreen, 2020). Unsuccessful aircraft programmes often result in the financial collapse of their manufacturers. Notable postwar examples are the Fokker F-100, the Douglas DC-10, and the Lockheed L-1011 (Spreen, 2020). More recently, Bombardier had to exit commercial aviation following the failure of its C Series regional jet.

Therefore, manufacturers tend to favour incremental innovations that build on existing aircraft in production. The bulk of single-aisle aircraft delivered today, such as the A320neo and 737 MAX, are derivative versions of aircraft programmes that have been running for decades; the first A320 was delivered in 1988, while the 737 was introduced in 1968. Efficiency gains could have been higher if the industry had focused on new aircraft programmes incorporating the full range of current technologies, like an all-carbon fibre fuselage. However, the development costs of such a clean-sheet design could be up to ten times more expensive:

In 2010, development costs for the Airbus 320neo, a derivative design of the original A320, were estimated by the manufacturer to be approximately $1.3 billion. By industry standards this was a modest sum, reflecting the limited scope of the program, which involved redesign of the existing A320 to incorporate new fuel-efficient engines, aerodynamic improvements to wings, and an upgraded cabin interior. Early estimates of development costs for recent technologically ambitious, completely new aircraft such as the Airbus A380 and the Boeing 787 have been in the neighbourhood of $15 billion, although many analysts believe that eventual total costs were closer to twice that amount (Spreen, 2020).

Typical derivative aircraft changes include stretching the fuselage to increase the number of available seats, improving aerodynamics with new wings or wingtip devices, upgrading the interior, and enhancing avionics. However, the most significant source of advancements across aircraft generations is the introduction of new engines.

With the exception of the airframe itself, engines have traditionally been the most expensive component of most aircraft. The engine suppliers compete on the basis of performance, economy, aftermarket support history, economics, and compatibility with engines installed in aircraft already in the buyer’s fleet (Spreen, 2020). Over the course of an aircraft’s service life, even minor differences in engine reliability, power, and fuel consumption will have a significant cumulative impact. Engine efficiency correlates directly to the distance an aircraft can fly, the amount of payload it can carry and, importantly, better environmental performance; consequently, the aviation industry has come to measure its technical progress in the increasing efficiency of its aircraft and engines (ATAG, 2010).

Therefore, engine efficiency has been a key driver of progress since the dawn of aviation. As fuel continues to be one of the highest costs of airline operations, engine efficiency remains one of the most crucial areas in which aircraft can progress. There is also a direct link between reduced fuel use and environmental impact: each tonne of fuel saved results in about 3.15 tonnes fewer CO2 emissions (ATAG, 2010).

The transition from turbojet engines to turbofan jet engines was a milestone in the evolution of commercial aviation. This new engine design was more than twice as powerful but much quieter and cheaper to operate than the turbojets it replaced (ATAG, 2010). Turbofan engines are designed to create additional thrust by diverting a secondary airflow around the combustion chamber:

The inlet air that passes through a turbofan engine is usually divided into two separate streams of air. One stream passes through the engine core, while a second stream bypasses the engine core. It is this bypass stream of air that is responsible for the term “bypass engine.” A turbofan’s 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, p. 7-21).

The higher the bypass ratio, generally the better the fuel consumption as more thrust is being generated without burning more fuel (ATAG, 2010). Logically, this relationship with fuel efficiency prompted aeroplane manufacturers and engine suppliers to continuously improve turbofan bypass ratios (Figure 7.7.1).

The first civilian turbofan engines had bypass ratios closer to 1. Given their superior performance, turbofan engines rapidly replaced turbojet engines. High-bypass turbofans were introduced in the 1970s, featuring a 5:1 bypass ratio. That is, there was five times as much air bypassing the engine’s hot core as there was passing through it. The latest generations of ultra-high-bypass turbofans feature bypass ratios of up to 12.5:1. Further increases in bypass ratio are possible with new aircraft designs configured to accommodate larger engines; however, the optimum ratio is limited by a trade-off between engine efficiency (larger is better) and engine weight and drag (smaller is better) (ATAG, 2021).

In addition to engines, structures and aerodynamics are significant areas in which commercial aircraft have undergone significant developments over the last decades. Drag is the number one enemy of aircraft designers; it is the aerodynamic force that opposes an aircraft’s motion through the air, and it is generated by the external surfaces of the aircraft (ATAG, 2010). Thus, with more drag, more fuel is used.

The emergence of new development tools, such as computational fluid dynamics (CFD), has enabled subtle but effective changes in aerodynamics. With more accurate and detailed aircraft performance estimation, manufacturers were able to improve aerodynamic performance through the development of enhanced wings and wingtip devices (Figure 7.7.2). Embraer’s second generation of E-Jets, for example, incorporates a new wing design that is thinner and longer than its predecessor. This new shape has increased the wing’s aspect ratio by 23.8%, resulting in a 3.5% reduction in fuel consumption, as reported by Embraer.

Manufacturers have also introduced newer types of wingtip devices designed to minimise drag. By incorporating winglets, whether on new aircraft or as retrofits to current models, airlines can save over 4% on fuel costs (ATAG, 2021).

In sum, each new aircraft generation has brought improvements in fuel economy and aerodynamic efficiency, but such incremental gains are getting more challenging to achieve. The industry foresees that future generations can still bring efficiency improvements of approximately 25 to 30%. However, further improvements to the tube-and-wing configuration powered by turbofans are becoming more and more difficult to conceive around 2035; in the longer term, towards 2050, radically new aircraft architectures will be required to reduce fuel burn and carbon intensity significantly (IATA, 2019a).