Tech

June 11, 2012

Army invests in technology that typically makes clocks work to increase helicopter transmission power

The U.S. Army Research Laboratory helped figure out 20 years ago a revolutionary way to increase transmission power in the Apache helicopter without increasing the transmission’s size or weight.

Split-torque face gear technology is now inside the Improved Drive System of the new Apache Block III helicopter that began delivery in October 2011.

With split-torque face gear technology, helicopters can now have more power without becoming heavier or bigger, said Lt. Col. David “Blake” Stringer, Ph.D., who is the chief, Vehicle Technology Directorate Field Element Office in Cleveland. With increased power density, the helicopter’s drive system now has advanced from a horsepower of 2,828 to 3,400, with growth potential, and the helicopter can fly longer, at higher altitudes carrying almost 200 pounds more weapons with a fuel tank – thanks to, essentially, basic scientific research begun by ARL decades ago.

The current Army objective is to field 690 AH-64D Apache Block III helicopters over the next 15 to 20 years. The initial production phase calls for 74 transmissions plus initial spares.

“Face gear technology is really unique because it allows you to send a lot more power through the same geometric footprint than you could normally do with any kind of conventional or other gear configuration,” he said. “The biggest benefit when we started the program was weight reduction. The initial projections from the project were 40 percent weight reduction compared to the current baseline Apache transmission.”

Face gears are a specific type of intersecting-shaft gears that have been traditionally used in positioning mechanisms such as clocks, but the Army found an application to use them in high power transfer applications. Think of gears as a circular disc, Stringer suggested. “The disc consists of the outer circular edge and two ‘faces.’ In spur or helical gears, the teeth are on the outer edge of the gear disc. In bevel gears, the teeth are set at some angle between the outer edge and the face. With face gears, the teeth are cut on the ‘face’ of the gear disc, or perpendicular to the edge of the disc.”

The tests that the Block III and the PM have had with the face gears has been incredibly successful, a lot more successful I think than they had anticipated and so we’ll just keep going and see how it evolves and if it’s as successful on Block III as it continues through the acquisition process, it will probably proliferate through most of the helicopter fleet eventually.

Transmission failure is the second most dangerous in-flight emergency after fires, Stringer said, which is part of the reason that the U.S. Army began an effort in 1988 to improve drive system technology. They focused most of their efforts on reducing aircraft weight and noise. He said the Army also undertook a project to find a way to keep the airframe itself in service much longer, and to develop technology for a future attack helicopter.

Propulsion experts in ARL’s Vehicle Technology Directorate in Cleveland, Ohio, teamed with industry, academic, and government partners on this effort, which is primarily studied and tested at the Glenn Research Center. The results led to the creation of the first use of face gears for high speed, high load rotorcraft applications.

“The Army and NASA relationship has been in place since 1970, right before this organization was part of the Army Research Lab. The facilities that have been here because of NASA funding and Army funding are not easily replicated anywhere else,” Stringer said from his office in Cleveland. “They’re unique. They’re always state of the art or better. And that Army-NASA relationship has enabled us – from both organizations – using people and resources from both organizations to really advance the state of the art, not just here in face gear technology but in engine technology, engine materials research technology and all other aspects of helicopter propulsion technology.

Other important contributors included Boeing, Northstar, the Army’s Aviation Applied Technology Directorate, the University of Illinois, NASA, and DARPA.

During initial research and testing, the team developed methods to control tooth contact, simulate meshing, and predict transmission error. They established tooth generation simulation tools and methods to define limiting inner and outer radii and performed initial experiments in-house to demonstrate the feasibility for the use of face gears in helicopter applications. Their studies projected that a split-torque, face-gear transmission gives a 40 percent decrease in weight compared to a conventional design for an advanced attack helicopter application. However, researchers say there’s benefit for just about any helicopter type.

Throughout the 1990s, VTD’s technical guidance helped design and conduct prototype testing. VTD also influenced the design of a face gear grinding machine, which was needed to manufacture high-precision face gears but was commercially unavailable. Gears used in helicopter power transfer applications are highly precisioned mechanical components. The gear tooth geometry is designed to a precise shape with very tight tolerances. This is needed to ensure smooth and proper meshing during operation as well as ensuring durability. The gears are made from high-strength, high-quality steel, undergoing many processes in fabrication to include carburizing and hardening. This is required to produce the high-strength mechanical properties but requires a final grinding step to achieve the accurate tooth profiles. Currently, there are only two machines in existence that are qualified to manufacture face gears for the Apache drive system. ARL tested gears produced on both machines to ensure that they met or exceeded required specifications.

He said face gears are being studied for use in other helicopter drive applications beyond Apache Block III.

ARL holds the institutional knowledge on face gear research and development, and on how to approach new, high-risk technologies, perform the basic and applied research tasks required for proving the concepts, and then transitioning those to the appropriate research, development and engineering center for development. This knowledge has enabled ARL to pursue other high-risk propulsion technologies in the areas of condition-based maintenance, advanced drives materials, and surface engineering techniques.




All of this week's top headlines to your email every Friday.


 
 

 
University of Rhode Island photograph by Tom Glennon

NASA kicks off field campaign to probe ocean ecology, carbon cycle

University of Rhode Island photograph by Tom Glennon The Research Vessel Endeavor is the floating laboratory that scientists will use for the ocean-going portion of the SABOR field campaign this summer. NASA embarks this week o...
 
 
NASA photograph by Carla Thomas

NASA’s high-flying laser altimeter to check out summer sea ice, more

NASA photograph by Carla Thomas This summer, the Multiple Altimeter Beam Experimental Lidar, or MABEL, will fly above Alaska and the Arctic Ocean on one of NASA’s ER-2 high-altitude aircraft. Sea ice in summer looks dramatica...
 
 
SOFIA

Outer space to inner space: SOFIA inside Lufthansa Technik hangar

NASA photograph by Jeff Doughty NASA’s Stratospheric Observatory for Infrared Astronomy is shown inside the Lufthansa Technik hangar in Hamburg, Germany where it is beginning its decadal inspection. Flight, aircraft maint...
 

 
NASA photograph by Tony Landis

New life for an old bird: NASA’s F-15B test bed gets new engines

NASA photograph NASA’s F-15B flight research test bed carries shuttle thermal insulation panels on its underbelly during a research flight in 2005. NASA Armstrong’s F-15B aeronautics research test bed, a workhorse at th...
 
 
NASA photograph by Tom Tschida

Towed glider benefits from center’s new 3-D printer capability

NASA photograph by Tom Tschida The major components of NASA Armstrong’s new high-resolution 3-D additive manufacturing printer occupy a shelf in the center’s subscale aircraft research lab. Robert “Red” ...
 
 
NASA photograph by Emmett Given

NASA completes testing on 3-D printer

NASA photograph by Emmett Given United Space Alliance engineer Cynthia Azzarita, left, and Boeing Company engineer Chen Deng, members of the Human Factors Integration Team at NASA’s Johnson Space Center, conduct a “...
 




0 Comments


Be the first to comment!


Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>