The Airplane - Jay Spenser [105]
Fanjets are quieter than turbojets because some of the fan’s air is ducted around the engine’s core rather than through it. This provides an insulating blanket of bypass air between the hot exhaust and cold ambient air. As for the sooty trails, improvements in combustor technology quickly eliminated those.
The first fanjet engines were low-bypass-ratio turbofans that ducted a relatively small amount of air around the core. Over the decades since then, engine developers have moved to higher bypass ratios and incorporated a spectrum of other technological enhancements. The result has been truly dramatic improvements in terms of fuel efficiency, airplane range, and noise.
There are some surprising things to know about modern fanjets. One is that propulsion reliability in the jet age does not depend on engine size, as it did in the piston era, when the most powerful radial engines were considerably less reliable than their lower-horsepower cousins. Modern aero engines are astonishingly reliable. The Boeing 777 world fleet offers a good example. In service since the mid-1990s, there are more than seven hundred of these twin-engine commercial transports in service as of this writing. These 777s are powered by Rolls-Royce, Pratt & Whitney, or GE fanjet engines. The GE90 fanjets powering the most capable 777 models are the most powerful turbine engines yet built. Each generates up to 115,000 pounds of static thrust.
Regardless of which engine type is fitted to its wings, a 777 will on average log about 25,000 flights and spend well over 100,000 hours aloft between each in-flight engine failure or precautionary shutdown. Most 777s will not reach these thresholds before being retired from service.
As for airline pilots, over a full career they might typically amass up to 25,000 logged flight-hours. Even if reliability rates stop improving, most pilots just starting out today can reasonably expect to fly an entire career without ever experiencing an in-flight engine shutdown. Nevertheless, crews of course train for them.
The Boeing 777, the world’s largest twin-engine airplane, has enormous fanjet engines that produce up to 115,000 pounds of thrust each.
Boeing
Even if a shutdown does occur, the remaining engine can take over without strain. This is ensured by rigorous government certification requirements that dictate twin-engine commercial transports must be able to suffer an engine failure at the worst possible time—on takeoff, when the airplane is flying slowly and at its heaviest—and climb out safely. For this reason, all twin-engine jetliners are 100 percent overpowered.
The planetary emergency that is global warming today focuses increasing attention on jetliner emissions. While great strides have been made over the years to increase fuel efficiency and reduce emissions of carbon dioxide and oxides of nitrogen, these continuing efforts are undercut by ongoing growth in the size of the world commercial fleet.
Aircraft and engine manufacturers, airlines, government agencies, and nongovernmental organizations are today collaborating to address the challenges of global warming. One area being examined is the substitution of more benign biofuels for kerosene, aviation’s current fuel. Also promising is the technology now being introduced by the ultraefficient Boeing 787 Dreamliner, the state of the art in aeronautical expertise. The 787 will use about 20 percent less fuel, and create correspondingly lower emissions, than similarly sized airliners. How it does this is the subject of a later chapter.
11 LANDING GEAR
SHOES, CANOES, AND CARRIAGE WHEELS
And once in a while when his landings are rusty, I always come through with, “By gosh, it’s gusty!”
—”THE COPILOT,” A 1941 POEM BY DC-3 COPILOT KEITH MURRAY
William Henson was the first human being ever to sit down and try to design an actual airplane. However unrealistic that might have been way back in 1840, it also made