Powering on: The evolution of the jet age


Power behind the flown

McDonnel Douglas manufacturing

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Every major advance in aviation has come from the engine


Since the dawn of the jet age, incremental improvements in propulsion technology have been crucial to achieving profitability and success for aircraft manufacturers and their airline customers

Donald Douglas Snr, arguably the USA’s greatest aviation industrialist, once said that “every major advance in aviation has come from the aircraft engine”. Despite it still being difficult to argue with that statement, aircraft manufacturers today are making impressive gains in operating cost reduction – and passenger enhancements – by tweaking almost every aspect of their designs to keep them current and marketable.

The drivers for this are the high cost and complexity of an all-new model and the overall lack of profitability in the industry – the last two years notwithstanding.

In the period between the 1950s and the late 1970s airlines were, by today’s standards, very profitable, thus enabling them to fund new designs. At the same time, the development of the jet engine from its humble and noisy turbojet beginnings to the high-bypass turbofan provided huge leaps in performance and operating economy, negating the need for large scale tweaking of existing designs.

Boeing, for example, launched four totally new designs in the space of 11 years between 1955 and 1966, while the other leader of the day, Douglas/McDonnell Douglas, launched three. What was emerging at the same time, however, was the proliferation of models and MTOW variations within those designs to meet broadening customer demand.

DC-10 & A320

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McDonnell McDonnell Douglas did not find it so easy to come up with a trijet successor to the DC-10

As airline profitability waned, particularly after the introduction of deregulation in the USA, aircraft manufacturers saw their traditional launch customer base evaporate, with a corresponding demand for derivatives.

McDonnell Douglas cited this change when it walked away from its 180-seat twin-aisle DC-11 in late 1980, unable to get a second US airline to join Delta Air Lines in launching the model.

It could be argued that the proliferation of models became an art form at Douglas prior to its 1967 merger with the McDonnell Aircraft Corporation. It initially struggled to rectify shortfalls in the DC-8’s performance, but then, with the launch of the DC-9 and Super DC-8s, it offered a wide range of models to combat Boeing’s family-of-jets concept.

The latter’s family was made up of a combined 15 variations of the 707, 727 and 737.

In a 2004 interview, the late Jackson McGowan, former president of Douglas Aircraft division of McDonnell Douglas, told Flight International that Boeing’s family approach to commercial aircraft was a winner and “very hard to combat”. Interestingly, the now forensic examination of aircraft to extract the smallest of gains can be traced to another McDonnell Douglas design – the MD-11. In 1991, the company discovered its trijet successor to the DC-10 was not meeting performance guarantees.

The company launched an exhaustive analysis and then clean-up of the design, finding benefits such as altering the windscreen wiper fairing to gain 0.3%. A seal package involving six modifications yielded a similar gain.

Airbus A19 & Boeing 737NG

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With the help of engine manufacturers, Boeing has kept the 737 more than competitive against several rivals, most recently the A320

Overall, the company’s seven-year, four-phase performance improvement packages essentially enabled the MD-11 to meet its original guarantees, although the aircraft’s problems did enormous damage to the manufacturer’s standing and were a significant factor leading to the merger with Boeing in 1997.

McDonnell Douglas and its suppliers were able to deliver a 3.5% improvement in drag and an improvement of up to 2.7% from the engines and nacelle. Meanwhile, take-off length was shortened by 270m (900ft) and structural weight was reduced by over 2,270kg (5,000lb).

However, the undisputed master of enhancements is Boeing and its 737, the world’s best-selling commercial jet aircraft, with 12,968 sold through to the end of September 2015. Launched 50 years ago against three other well entrenched competitors, Boeing – with the help of engine suppliers – has been able to keep the aircraft current while seeing off the early rivals, and since 1984 keeping parity with the Airbus A320 family. Since it was launched in March 1984 through to September 2015, the A320 family has drawn 409 more orders than the 737, for a total of 12,239 (Boeing had sold 1,138 737s up to March 1984).

The intense rivalry between the two aerospace giants and their engine partners, combined with the generally poor levels of airline profitability, has seen a host of innovations across every aspect of the two aircraft designs and systems both inside and out.

The two manufacturers have leaned heavily on newer widebody programmes and engine suppliers to deliver everything from the smallest to the most significant gains.

In this special case study we examine the two best-selling commercial jets from Airbus and Boeing, and find a relentless drive to extract the smallest gain for the slightest edge.