Technology Update

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March 2002
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Boeing looks to the future

Saw-tooth-shaped aerodynamic devices on the exhaust nozzle can be used to control the mixing of the hot jet exhaust, the bypass stream, and the ambient air.

Following the selection of Lockheed Martin's X-35 for the Joint Strike Fighter program, The Boeing Co. has begun focusing its attention on other areas in the industry such as intelligent vehicle technology, power systems, and noise control.

The company recently was awarded a $50 million Intelligent Vehicle Research Initiative contract by the NASA Dryden Flight Research Center (DFRC) in Edwards, CA. The first task under the contract will be to establish a REsearch FLight Control System (REFLCS) to allow research into technologies such as intelligent flight controls.

According to NASA Intelligent Vehicle Program Manager Jerry Henry, also under future consideration as a research topic is an emergency autopilot system that could take complete control if an aircraft was heading toward imminent danger or obstacles.

Flight testing of engine monitoring systems began in October 2001 at Edwards AFB. REFLCS will be installed on a C-17, then flight-tested during the third quarter of 2002. In early 2003, C-17 flight tests will be initiated at Dryden. Program goals include providing a flexible research environment on a large transport aircraft, demonstrating damage-adaptive technologies, and transitioning NASA technologies to operational aircraft in the field.

Engine number three on the C-17 test aircraft will have prognostic sensor groups installed to detect and monitor potential ingested debris and engine distress. The first-generation sensors are installed and are currently being evaluated. In addition, the C-17 will test systems that monitor high-frequency vibration, stress wave analysis, and wireless sensing.

Initial research with this technology began in 1995 at NASA Ames Research Center, CA, where the Intelligent Flight Control software developed by Phantom Works was demonstrated in simulators.

As part of a separate study, the aircraft manufacturer will develop and test an electrically powered demonstrator airplane to evaluate environmentally friendly fuel-cell technology for future Boeing products.

The airplane manufacturer's new Research and Technology Center in Madrid will modify a small single-engine airplane by replacing its powerplant with fuel cells and an electric motor that will turn a conventional propeller.

Fuel cells and electric motors will not replace jet engines on commercial transports, but they could one day replace gas turbine auxiliary power units, believes Boeing. Auxiliary power units (APUs), which typically are located in the rear fuselage with exhaust ports through the tail, are coupled to generators and compressors to produce electricity and air for airplane systems while on the ground and for backup use in flight.

"Our ultimate goal is to replace the APU," said Dave Daggett, associate technical fellow in the environmental performance strategy group. "But first, we're going to learn more about fuel cells by powering a small airplane and, as the technology matures, use fuel cells to power aircraft electrical systems."

Fuel cells are inherently cleaner and quieter than typical auxiliary power units. They have fewer moving parts and can generate more than twice as much electricity with the same amount of fuel.

"Fuel cells show the promise of one day providing efficient, essentially pollution-free electrical power for commercial airplane primary electrical power needs," Daggett said.

Most of the work on the electric airplane will be done in Europe. Boeing Madrid will design and integrate the experimental airplane's control system. NASA, fuel-cell manufacturers, the automotive industry, and several European universities are supporting the project. Test flights are scheduled to begin in early 2004.

In the area of noise reduction, Boeing has participated in a program with Rolls-Royce. Known as the Quiet Technology Demonstrator (QTD), a Rolls-Royce Trent 800 engine was modified with a package of noise-reduction technologies developed collaboratively by the two companies. The modified engine was fitted to a 777-200ER and flight tested over a three-week period in which the aircraft demonstrated noise levels significantly below those of a standard 777, which is regarded by Boeing as one of the quietest airplanes currently in service. Takeoff jet exhaust noise was reduced by up to 4 dB, and inlet fan noise was reduced by up to 13 dB.

Engineers used saw-tooth-shaped aerodynamic devices at the rear of the nacelle and on the exhaust nozzle to control the mixing of the hot jet exhaust, the bypass stream, and the ambient air. The shape of the devices was determined by computational fluid dynamics modeling and verified in wind tunnel tests using scale models.

Fan noise also was reduced with extensive acoustic improvements to the redesigned engine nacelle inlet. A new technology called Amax (area maximization) increased by 30% the area of acoustic treatment in the inlet casing. Also, a new lining design that reduces objectionable "buzz saw" noise passengers often hear during takeoff and climb was used.

Conducted at Boeing's Glasgow, MT, airfield, the flight tests verified computer and laboratory results. Some 200 microphones were placed on the ground along the flight path, and 100 microphones were affixed to the 777. Teamed with computers, the microphones became an "acoustic camera" that dynamically pinpointed high-frequency noise sources on the airplane as it took off, flew the flight-test pattern, and landed.

Although the purpose of the QTD program was to reduce noise heard on the ground, levels within the cabin—equally important to the airlines—also were analyzed. Nearly 100 microphones placed along the entire length of the cabin registered a reduction of forward cabin buzz-saw noise by 7 dB.

Combined with airframe noise reduction and engine redesign efforts being pursued separately, the new technologies can be incorporated on a new airplane program or as a retrofit to airplanes in service.

- Frank Bokulich

March 2002
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