Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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7.2.2 Aircraft Historical and Future Developments
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The cruise speed of 1940s propeller-driven aircraft increased from about 100 to 300 knots over a period of 20 years, as shown in Figure 7-1 for Boeing and Douglas
aircraft (Condit, 1996). At the start of the commercial jet age, at the end of the 1950s, cruise speeds were about 450 knots. The majority of turbofan-powered aircraft in
today's world fleet have average cruise speeds of about 500 knots (Jane's, 1998).
Airworthiness requirements determine the range of safe operational speeds for a given aircraft
type. Actual speeds for any given flight will be determined by air traffic control considerations
and by individual airline performance management system techniques, the latter taking due
account of the need for fuel efficiency. These operational aspects are discussed in Chapter 8.
In the period mentioned above, the cruise altitudes of propeller driven aircraft have risen from
about 3 to about 7.5 km, as shown in Figure 7-2. For longer range jet- and turbofan-powered
aircraft, average cruise altitudes have remained fairly constant over the past 35 years at 10.5 to
11.5 km, although, since the initial turbofan-powered aircraft were designed, there has been a
slow rise in maximum cruise capability. Some aircraft can cruise up to about 13 km. Aircraft will
sometimes fly below optimum design cruise altitudes for reasons associated with air traffic
control or severe weather conditions (storms and clear air turbulence). Flying at lower cruise
altitudes can significantly increase fuel burn (see Chapter 8) depending on range and passenger
load.
The civil aircraft fleet average for speed and cruise altitude is not expected to increase
significantly beyond 500 knots and 13 km over the next 50 years, as a result of physical and cost
limitations. The high cost of developing new aircraft has led to the adaptation of baseline designs
to increase payload and range. Increased weight generally requires more thrust, which can
mean using new engines or increasing the performance of existing engines using the "throttle
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Figure 7-1: Transport aircraft cruise speed progress.