Rolls-Royce learns the ropes

HRS Services used rope access for technicians checking a Rolls-Royce "golf ball" test rig for delaminations.

What do you do when your aero engine "golf ball" test rig needs inspection for possible delamination and you know that scaffolding itself may cause damage? You use rope. UK-based specialist, HRS Services, has completed a non-destructive test survey of Rolls-Royce Aero Engines' "golf ball" rig. They worked with inspection and materials testing specialist company, CoMech.

There was concern that delamination of the panels in the test rig could lead to fragments being sucked into jet engines. Accurate failure prediction is essential. Each panel in the test rig is unique in terms of size and fixing. The panels are also fragile, and scaffolding access to them was thought to cause possible damage. CoMech therefore used a light alloy tower for inspection. However, it could not provide access to panels in the crown of the test rig. But HRS, which specializes in accessing difficult structures, was able to use trained operators lowered by ropes from the frame of the structure erected to give weather protection to the test rig. They used ultrasonic equipment to check all remaining panels.

- Stuart Birch

P&W's ceramic turbine for UAVs

Pratt & Whitney is developing advanced ceramic turbine components for future U.S. Army UAV engine applications.

The U.S. Army's Aviation Applied Technology Directorate (AATD) has awarded a 39-month contract to Pratt & Whitney (P&W) to develop critical turbine technologies to support a future 500 shaft-hp engine demonstration program. P&W will work in conjunction with the United Technologies Research Center to develop an advanced turbine component to support potential unmanned aerial vehicle (UAV) applications and objective force systems. The program is valued at more than $2 million.

The engine is expected to exploit ceramic technology to achieve a 20% reduction in specific fuel consumption, a 50% improvement in power-to-weight, and a 35% reduction in production costs. AATD anticipates a demonstration of the heavy-fuel engine sometime in 2004. P&W efforts include the pursuit of ceramic turbine technology for dynamic engine components, produced in a low-cost, repeatable process. According to Kevin Farrell, General Manager of Small Military Engine Programs, P&W, the use of ceramic hot-section components allow for lower cost and higher-performance engines. "The challenge has been to be able to repeatedly produce quality ceramic products," he said. He added that the opportunities for the technology would include both UAVs and manned aircraft.

- Jean L. Broge

Silencing aircraft

Rolls-Royce is working with SNECMA, MTU, and Airbus on the European SILENCE(R) program. Click to enlarge

The reduction of noise pollution by commercial aircraft engines is a continuing challenge for the aerospace industry in general, with the problem likely to be compounded by the rise in air-traffic movements over the next decade. All major aero engine manufacturers and many of their suppliers have programs in place that aim to reduce noise. In Europe's skies and above its crowded countries, the problem is particularly acute and 51 companies are currently taking part in a European Commission research program called SILENCE(R) (SIgnificantly Lower aircraft Environmental Noise Community ExposuRe) to investigate new technologies that may lead to major noise reduction. (See Aerospace Engineering, November 2002.)

The program is the third integration phase of the EU's aircraft noise reduction campaign and is slated to be completed in 2005. It aims to lead to an overall reduction of engine noise of 6 dB by the year 2008, says the Munich-based aero-engine company, MTU. It believes by 2017 that reduction could reach 10 dB effectively halving the noise level of a typical modern jet airliner engine.

Begun in late spring 2001, the program involves 14 EU countries plus two—Romania and Switzerland—outside the EU. Half the cost of the program (€110 million) is being supplied from EU funds, with industry funding the rest. MTU is among the major companies involved in the program, which is aimed at a large-scale integration of the noise-reduction technologies whose development was initiated by EU and national projects in 1998. As well as creating new technologies, SILENCE(R) will also assess their applicability to future European products.

MTU's particular focus is the design of low-noise compressors and turbines and it heads a working group that is exploring engines with ultra-low bypass ratios. Due to the relatively low velocity propulsive jet of these engines, MTU believes there is the potential for "substantial" noise reduction. To exploit it, however, the 6:1 to 8:1 bypass ratios of current engines would have to grow to 12:1 and over. Achieving that goal demands larger fan diameters that would allow the fan to turn at lower speeds. But this creates problems, with the low-pressure turbine driving the fan operating below its optimum speed range, for which it is necessary to use a geared fan that allows the fan and low-pressure turbine to turn at individually optimum speeds: As well as the ATFI (Advanced Technology Fan Integrator) that MTU developed in co-operation with Pratt & Whitney and Fiat, MTU had previously worked on a high-speed, low-pressure turbine and can now channel its findings into the SILENCE(R) project.

It is because the major noise sources—apart from the fan—of an aircraft on approach are known to be the compressor and turbine that MTU is focusing its work on them. Under a TurboNoise CFD research program, MTU is using advanced numerical codes to identify major noise sources and determine optimization potentials. One of these is the so-called "cut-off design." It uses varying blade counts in the rotor and stator stages and causes noise generating pressure waves to spread out instead of traveling back toward the exhaust, resulting in "substantial noise reduction."

The use of active noise reduction, using similar systems that have been applied to reducing cabin noise, is also being studied in collaboration with the German research organization, DLR. As in the cabin system, microphones are placed in the engine intake and loudspeakers used to generate an anti-phase sound field.

Rolls-Royce Aero Engines is also closely involved with noise reduction and has similarly cited a 10 dB noise-reduction target. It is also a partner in SILENCE(R) with MTU and the French company, SNECMA, together with Airbus. Rolls-Royce has worked with Boeing on a joint technology program focused toward achieving quieter commercial aircraft engines. Their Quiet Technology Demonstrator involved flight testing on a Boeing 777 late in 2001 of a Trent 800 powerplant modified with a package of technologies developed jointly by the two companies. Rolls reported that the test "exceeded expectations," with jet noise reduced by 4 dB, fan noise by 13 dB, and a "significant" overall noise reduction. Further tests are to be carried out. According to Rolls, the work so far is one of the most comprehensive test programs ever undertaken to reduce engine noise.

The work started with static testing in 1999. Original targets for the flight test were jet noise reduction of 3 dB and fan noise reduction of 7 dB, so the results achieved far exceeded expectations. As well as serrated nozzles, the engine also has advanced acoustic linings within the intake cowl, known as Amax (Area maximization). This feature effectively increases the area of acoustic treatment in the inlet cowl by 30%. The result is a reduction of "buzz saw" noise that can be very intrusive for people on the ground.

- Stuart Birch