Introducing ....... Boeing's Electric 7E7.
Introducing ... Boeing's electric 7E7
Commercial plane will be the first with such efficiency
Thursday, May 20, 2004
By JAMES WALLACE
SEATTLE POST-INTELLIGENCER AEROSPACE REPORTER
EVERETT -- In twin, four-story office buildings constructed here for 777 engineers more than a dozen years ago, a new generation of Boeing Co. aircraft designers are pushing the envelope further than ever before.
Working with airlines and Boeing's partners, they are designing the world's first electric commercial jetliner -- the 7E7.
Much has been made of the new jet's composite wings and fuselage, its cabin innovations and the next-generation, fuel-efficient engines. But just as significant to the success of the 7E7 (the "E" stands for efficiency) is this pioneering approach toward a more electric airplane.
For the first time, Boeing recently allowed the engineer leading this effort to provide a detailed look at the systems that will give the 7E7 a competitive edge.
It is a plane that that will have far fewer computers than current commercial jets, miles less wiring and a revolutionary way of electrically powering some critical systems, from the brakes to the de-icing mechanism in the wings.
Even the 7E7 engines will be started electrically -- a radical change that initially concerned airlines.
"This is groundbreaking," said Mike Sinnett, Boeing's chief engineer for 7E7 systems, who formerly led the systems work on the now-canceled sonic cruiser program. "We think this is the way of the future."
"The industry has kicked this around for a long time," he said. But the state of the technology was such that designing an electric jetliner was not possible -- until now.
Jetliners are not nearly as efficient as they could be. More pneumatic power, for example, is created than is required from a systems standpoint. This power comes from huge amounts of "bleed air" diverted from the jet engines. It not only makes the engines less efficient but some of the bleed air is dumped overboard before it can be used, adding to the overall inefficiency of the plane.
Carried by a network of ducts through the plane, the bleed air must go through check values and precoolers before it can be used. Even then, it is not used as efficiently as electrical power.
"You have all this high-pressure, high-temperature air coming off the engines and the airplane can't accept air with that much energy," Sinnett explained.
On the 7E7, Boeing will eliminate this bleed air, other than a tiny amount to help with engine stability at idle settings.
As a result, there will be no need for the network of titanium ducts, which are expensive to make and add hundreds of pounds to a plane's weight.
Systems once powered pneumatically will use electricity, supplied by two 225-kilowatt generators attached to each of the 7E7's two engines. The auxiliary power unit, or APU, in the plane's tail will also have two of these generators.
"Part of the idea of going to a more electric airplane is that all these components that are used to generate pneumatic power are eliminated and ... we only create the power we need," Sinnett said.
Today's jet engines always operate at higher thrust settings to create bleed air, even if it is not used.
Engine makers, according to Sinnett, have often told Boeing: "Gee, you guys keep robbing bleed air from us and you are making it harder for us to do our jobs."
So Boeing came back, he said, and told the engine makers: "OK, if you are really serious, we will eliminate that bleed air. "
The engine makers were stunned, Sinnett said.
"They said, 'Whoa. Wait a minute. What are you guys talking about? This is a very big deal,' " Sinnett recalled
Boeing recently picked General Electric and Rolls-Royce to supply the new 7E7 engines.
The new approach is possible because of advances made in power electronics technology.
"The problem has always been that we were not able to create generators that from a size and weight standpoint are efficient enough to create the power that you need," Sinnett said.
Today's jets use a complex system on the engines that coverts variable frequency power into constant frequency. This is no different than what happens with electricity going into a home. The power must be of the same frequency.
On jets, this process is accomplished using what is called a constant speed drive. Such drives are typically complex, heavy and prone to failure.
The 7E7 will be able to take variable frequency power from the engines and "condition it" for use by the various aircraft systems. This will done in the electronics bay of the plane rather than on the engines.
"We can create four times as much (electrical) power on the 7E7, but we only create what we need," Sinnett said.
With the elimination of bleed air and pneumatic power, a range of systems will, for the first time, be powered electrically on the 7E7:
The de-icing system. The leading edge of the wing will be heated electrothermally, rather than pneumatically.
The overall hydraulic system is more electric because air-driven pumps have been eliminated. Large, pneumatic pumps are used to raise the landing gear on jetliners. This will be done electrically on the 7E7.
Boeing is evaluating the use of electric actuators for some secondary flight controls that now are powered hydraulically.
On today's jets, cabin air comes from the bleed air system on the engines. The air is hot and dry and must be cooled. On the 7E7, cabin air will come directly from the outside. Less energy will be needed to make it suitable for the cabin.
Brakes are activated hydraulically on today's jets using a complex and expensive plumbing system. On the 7E7, brakes will be controlled by electric motor driven actuators, with four on each wheel.
The auxiliary power unit on the 7E7 will be far simpler. On today's jets, the APU unit has a complex load compressor to supply pneumatic power. The compressor is eliminated on the 7E7, and the APU becomes a jet-fuel powered electrical generator.
Sinnett said the 7E7 will also incorporate a number of other advances beyond the move away from bleed air:
Hydraulic power will be distributed at 5,000 pounds per square inch, rather than the standard 3,000 psi. Less fluid will be needed and smaller hydraulic lines.
Electrical power will be distributed remotely instead of running everything from a central center. As much as 60 miles of copper wiring will be eliminated. And the wiring that is used will be smaller gauge and lighter weight.
Given how far Boeing is pushing the design envelope with the 7E7, some airlines have at times expressed concern whether this new way of doing things will be as reliable as what they have today, Sinnett acknowledged.
One concern has been with the way the 7E7 engines are started electrically.
Typically, jet engines have air turbines, one of which is started with high-pressure bleed air from the APU when it is fired up.
On the 7E7, the APU will supply electrical power to fire the generators on the engines, which will act as starters.
If an APU fails on today's jets, such as the 767, the engines can be started by ground trucks that supply pneumatic power. But some airlines were worried that if the APU on the 7E7 did not work, there would be no way to start the engines.
"We are now going through the process of figuring out how to configure the plane to accept external electrical power to start the engines," Sinnett said.
For airlines, the advantages of operating a more electric plane are enormous, Sinnett said.
The cost of overhauling brakes will drop substantially. There will be no more ducts that require periodic inspection and maintenance. Power is not wasted. Efficiency is improved. Weight is saved
And for Boeing, it means the 7E7 will have a significant advantage over the competition, Sinnett said.
The main competitor to the 7E7 will be the Airbus A330-200, which was introduced in the late 1990s and has been clobbering Boeing's 767 in sales.
Airbus has said it is not worried about the 7E7 -- it will add the more efficient engines designed for the 7E7 to the A330-200 and make other improvements as needed.
But given the significant changes being designed into the 7E7 from the start, Sinnett said, there is no way that Airbus can alter an existing plane and make it as efficient.
"You have to look at the total integrated package of an electric plane," he said. "You can't take one piece of that and put in on a non-electric plane and expect anything out of it."