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Boeing 787 Dreamliner Rolls Out Smoother Ride with Gust Suppression
Dreamliner’s gust suppression system senses pressure differences before inertial motion begins
Charles J. Murray, Senior Technical Editor -- Design News, June 3, 2007
Just thinking about it is enough to make you queasy: A commercial airliner hits a pocket of turbulent air; its nose pitches up, then down, then heaves back up again. Meanwhile, the mighty ship yaws; it rolls to starboard; it rolls to port. In the midst of this event, which may last two to three minutes, even the most experienced fliers glance at the air sickness bags in the seat pockets in front of them … just in case.
If Boeing engineers have their way, however, that scenario may disappear, or at least be transformed into something much milder. That’s because the aerospace giant has endowed its 787 Dreamliner with a smoother ride technology that could help reduce the pitching, rolling and yawing that occurs when airliners are struck by powerful air gusts.
“We’ve focused on the kinds of frequency responses and frequency bands that cause motion sickness,” says Mike Sinnett, chief project engineer for Boeing 787 Systems. “We look at events that can last between one and five seconds and we’ve got plenty of frequency response in the airplane to work with.”
Indeed, the 540,000-lb mass of the 787 gives engineers a lot to work with. Such enormous masses don’t ordinarily respond instantly, even to the biggest wind gusts.
But the real innovation behind Boeing’s smoother ride technology lies, not in the aircraft’s mass, but in its electronics and software. To maintain stability, Boeing engineers use a combination of technologies like those in an automobile’s stability control system. Sensors around the aircraft measure changes in angular velocity and pressure distribution. Wind gusts that cause yaw, pitch or roll, for example, are detected and recorded by gyroscopic sensors. Similarly, vertical and horizontal forces on the craft are measured by accelerometers. At the same time, pressure sensors detect pressure distribution changes around the skin of the airplane through a selected (but unspecified) number of static air intake ports.
All of the sensor data is then sent to central processing units around the airplane. Boeing engineers won’t say how many or what kind of microcontrollers process that mountain of sensor data, but big commercial aircraft typically have more than a hundred electronic control modules, usually governed by a few master controllers. During flight, the controllers take in the data, apply proprietary software algorithms and determine what course of action to take. Using fly-by-wire techniques, the controllers then send signals to electric motors that actuate the rudder, elevators, spoilers, ailerons and flaperons. As a result, the aircraft autonomously actuates the control surfaces it needs to correct its own inertial reaction to the wind gusts.
“If the airplane is hit by a lateral gust, for example, we counteract it by suppressing the reaction to that lateral gust,” Sinnett says.
To be sure, other aircraft manufacturers have previously implemented such systems. But Boeing engineers say the 787’s smoother ride technology takes the state of the art to a new level.
“We don’t just sense the inertial response and then counteract it,” Sinnett says. “We sense a pressure differential and we counteract the pressure differential prior to the inertial response of the airplane.”
If, for example, a strong horizontal wind gust hits the aircraft, the system calculates the pressure differential across the vertical fin of the aircraft, then moves the rudder to counteract that gust. All of this happens before the aircraft’s inertial response, which is why engineers have unofficially dubbed it a “gust suppression” system.
This ability to anticipate the plane’s inertial response is what separates Boeing’s efforts from previous ones. It also could be the key to reducing the nauseous feeling that accompanies flight through turbulent air.
Experts say the aerospace industry has been on the cusp of realizing such visions in commercial aircraft for years. “With a large aircraft, there’s always a time lag between the change in the angle of attack and the lift that’s produced,” says Rakesh Kapania, a professor of aerospace engineering at Virginia Tech University. “Using the right math and the right physics, it’s definitely possible to take advantage of that time lag.”
Dealing with Motion Sickness
As a company, Boeing says it has teamed with universities around the world to study how the human body reacts to flight conditions. Its studies – which detail the effects of altitude, humidity, pressure, sound, lighting and space on passengers – have led engineers to conclude the real culprit in turbulent flight is the repeated up-down motion of a plane through turbulent airstreams.
“If you’re driving your car down a bumpy road made of bricks, that doesn’t cause motion sickness,” Sinnett says. “But if you drive down a road with a series of hills, where each hill is about 10 seconds apart, that’s when people start getting sick.”
Similarly, Boeing is targeting vertical wind gusts that cause an airliner to respond in a frequency band very much like that of a car going over a series of hills. Engineers say they are focusing on those longer-period events – lasting typically from one to five seconds – because those cause motion sickness.
As such, the gust suppression electronics don’t necessarily have to enable the aircraft to react in the blink of an eye.
“The airplane is a big inertial mass,” Sinnett says. “Even though the gusts come and go very quickly, it takes a discrete amount of time for the airplane to react inertially. If you compare computational speed to the inertial reaction time of a large mass like an airplane, it’s like comparing clock time to geologic time.”
Boeing engineers say software (which they will not discuss for competitive reasons) is the key to reading each situation and reacting appropriately. By intelligently examining the sensor data and pressure differentials across the aircraft, the Dreamliner’s software algorithms enable the fly-by-wire electronics to suppress wind gusts before the plane begins to pitch, roll or yaw.
“We run computations many, many, many times per second,” Sinnett says. “We have enough time to close the loop and send commands to the control surfaces before the plane can respond inertially. That’s what keeps people from getting sick.”
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Dreamliner to Employ Bigger Windows, Higher Cabin Pressure, More Humidity Composite materials will make 787 flight more comfortable |
Although Boeing’s smoother ride technology is likely to take center stage when the 787 Dreamliner rolls out, Boeing engineers have also added other features aimed at making flight more comfortable. The company, which has teamed with universities around the world to study how the human body reacts to flight conditions, will also incorporate the following features in the Dreamliner: Simulating Lower Altitudes. Unlike conventional aircraft cabins, which are pressurized to simulate an altitude of 8,000 ft, 787 cabins will simulate a 6,000-ft altitude. Working with Oklahoma State University to study altitude effects, Boeing engineers concluded passengers would experience meaningful improvements at a simulated 6,000-ft altitude. Doing so, however, means greater cabin pressurization, which in turn places more mechanical stress on the aircraft’s skin. Use of advanced composite materials, however, enables the 787’s fuselage to withstand the greater pressurization without undue fatigue. Humidity and air purification.In the Dreamliner, Boeing will increase humidity and add gaseous filtration technology, thus reducing the effects of dry airplane air. Working with Denmark Technical University, Boeing found that humidity is not the only factor that causes post-flight symptoms of dryness, such as eye and throat irritation, as well as headaches. By employing so-called “gaseous filtration technology,” the 787 will be able to filter out gaseous molecules that can’t be filtered out by HEPA filters. Bottom line: Symptoms associated with dryness will be reduced by 50 percent. Bigger windows.Studies have shown passengers want bigger windows. Structurally, however, bigger fuselage cutouts have been a problem in the past. By making greater use of advanced composites, rather than aluminum, Boeing engineers were able to incorporate larger windows than any of today’s current commercial airplanes. Visit Design News' 787 Dreamliner coverage page for more stories and podcasts on Boeing's newest aircraft! |
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Boeing 787 Dreamliner Joins Auto Industry in Use of Stability Control Systems Use Same Sensors, Similar Microcontrollers |
Boeing’s 787 Dreamliner isn’t the only product to employ smoother ride technology. Automobiles have implemented yaw-stopping stability control systems for more than a decade. In many ways, the similarities between the systems are striking. Both use gyroscopic-type sensors to sense angular acceleration. Both use linear accelerometers to detect lateral forces. Both also use microcontroller-based electronics modules to make decisions and send signals to actuators. On the 787, electric motors actuate control surfaces, such as ailerons, elevators and rudder. On cars, hydraulic pumps and cylinders actuate brakes. The main difference between the systems is Boeing’s use of static air intake ports to measure pressure differentials across the plane. By doing so, Boeing’s smoother ride technology can take action before the pitching, rolling and yawing begin. Although Boeing engineers won’t talk about the kinds of electronic components they use, makers of microcontrollers say that aerospace customers traditionally use components that are closer to the state of the art. The aerospace and military industries are OK with the prices of the best components,” says Ram Sathappan, a marketing manager for the Digital Signal Processing Group at Texas Instruments. “Because of the volumes and costs of commercial aircraft, price isn’t as big an issue for them as it is for automakers.” |
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Boeing 787 Dreamliner Rolls Out Smoother Ride with Gust Suppression
Dreamliner’s gust suppression system senses pressure differences before inertial motion begins
