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Sunday, October 1, 2006

HUMS

David Jensen

Health and usage monitoring systems (HUMS) for helicopters amass plenty of data. Now efforts are being made to put that information to better use.

Like divers salvaging the contents of sunken ships, the manufacturers of health and usage monitoring systems (HUMS) are plunging deeper into the data their devices produce and discovering a treasure trove. Perhaps more importantly, they are developing algorithms that will make greater use of the data and expand their HUMS' capabilities. HUMS technology is not new. It was developed in reaction to a concern over the airworthiness of helicopters. Vertical-lift aircraft have many more safety critical rotating components, the failure of which could be catastrophic. The purpose of HUMS is to increase safety and reliability, as well as reduce operating costs, by providing critical component diagnosis and prognosis. The first flight of a certified HUMS was on a UK offshore support helicopter in 1991. Eight years later, the Federal Aviation Administration issued an advisory circular (AC-27-1/AC-29-2) that serves as guidance for HUMS installation. Acceptance of HUMS continues to grow; the system is standard, for example, on the Sikorsky S-92 and an option on the Agusta Westland AW-139. Operators are retrofitting their fleets, as well. Columbia Helicopters, a Portland, Ore.-based heavy-lift operator announced earlier this year that it would outfit its Boeing rotorcraft with the Honeywell XVP health and usage monitoring system. The XVP also is a factory option on the Sikorsky S-76C+ and Eurocopter EC-135. HUMS' ability to improve safety and reliability has long been verified. Goodrich Corp., a maker of HUMS for many U.S. military helicopters, reports a recent example, in Iraq. A comparison of two Black Hawk units within the 101st Airborne, one with HUMS and one without the system, reveals that the equipped unit flew 27 percent more missions and maintained a higher readiness rate than the non-equipped unit, according to Kip Freeman, business director for vehicle health systems in Goodrich Government Systems. HUMS performs its diagnostic and prognostic roles by gathering meaningful data that can be used to modify required maintenance and the flight crew's operational actions. The system typically comprises a variety of sensors (including accelerometers for vibration data) and data acquisition systems. They monitor main-rotor track and balance, limit exceedance and the health of the engine(s), main-rotor transmission, gearboxes and airframe. The systems also include crash-protected voice and flight data recording, comparable to commercial fixed-wing systems. The acquired HUMS data may be processed onboard the aircraft or in a ground station against defined criteria.

HUMS on the 47
Two major HUMS manufactures, Goodrich and Smiths Aerospace, have developed software that enhances data processing and analysis to unearth new capabilities from the information their systems provide. The capabilities are to be made available for all rotorcraft types, but much focus currently is on the CH-47 Chinook helicopter. Goodrich, for example, has been demonstrating the capability of balancing the main rotors on the tandem-rotor Chinook without the use of a tracking device. The company has found that, with an advanced algorithm, its Integrated Mechanical Diagnostic HUMS (IMD-HUMS) can determine more precise solutions to smooth out rotor systems by making more detailed calculations of the vibration detected by accelerometers in the helicopter's cabin. In other words, it simply makes greater use of the data normally gathered by a HUMS. Although the IMD-HUMS can include a tracker to augment the vibration data, the algorithm negates the need for such a device, which is an infrared (IR) camera pointed at the main rotor. The tracker sends out an IR signal that bounces off the rotor blades, and the signal return is measured to determine the height of each rotor blade. When the blades are at different heights, the noise and vibration of the helicopter increases in a manner similar to the rotor head itself, being out of balance. Goodrich's trackerless concept has been proven on IMD-HUMS-equipped Sikorsky CH-53s, H-60 Black Hawks and Seahawks, and Bell AH-1s and UH-1s-helicopters with a large, single main rotor and smaller tail rotor. But the current demonstration, launched in late 2005 on a Pennsylvania Army National Guard CH-47, has proven that the concept also works on helicopters with equal-size, tandem rotors. "We found we could balance both rotors on just one try," says Freeman. "With trackers, it often takes more than one try." An Army goal with HUMS is to achieve condition-based maintenance, and to help achieve the goal Goodrich has developed an automated watch list that reports the status of components that typically require a lot of maintenance. The high-speed engine output shafts are reported in such a list. The result has been to automatically report those shafts that require balancing and those that do not. In addition, if a maintenance action is unsuccessful, the watch list immediately reports the adverse outcome to the maintainers so that they can schedule additional corrective maintenance during the next 40-hour inspection. Goodrich has been working on this program over the past nine months. The RAF operates 40 HC Mk II Chinooks; all are fitted with Smiths' HUMS. Smiths' system continuously provides rotor track and balance, so there is no need for special testing and to carry special equipment on board. Smiths, too, is conducting a demonstration program involving Chinooks. At RAF Odiham, the company and Royal Air Force have been evaluating software that provides a new means of processing the structural load data on an HC Mk II Chinook. This exercise is to give the RAF a "rough cut" evaluation of how the aircraft are being used in certain regimes and the consumption of its components' structural life. Traditionally, attaining such data has meant pulling three or four aircraft out of use and installing strain gauges and a recording system to monitor operational loads, given the flight spectrum profile. However, with a mathematical model developed by Smiths, the data gathering and processing is done continuously, like the rotor tracking. According to Piet Ephraim, Smiths' director of strategic development for information systems, the model uses the HUMS' existing measurements of flight parameters to synthesize component-life consumption. In July, Boeing contracted Smiths to provide a Chinook HUMS for demonstration for U.S. Army's 160th Special Operations Aviation Regiment (SOAR). The regiment operates the MH-47G, which is comparable to RAF's Chinooks but has digital, rather than analog, avionics. A flight trial is scheduled for January 2007. While the trial is for SOAR's 47Gs, Ephraim says the Army has contracted Boeing to assess the development of HUMS requirement specifications for the service's entire Chinook fleet.

Other Developments
In addition to upgrading the HUMS in RAF Chinooks, Smiths recently announced a $21-million contract to develop and supply HUMS and cockpit voice and flight data recorders (HUMS/CVFDRs) for 70 Future Lynx helicopters for the British Ministry of Defence. The systems will be integrated into 40 battlefield reconnaissance helicopters for the British Army and 30 surface combatant maritime rotorcraft for the Royal Navy. HUMS deliveries are scheduled to begin in 2011. Smiths also is developing a HUMS for Korea's new multirole helicopter, meant to replace the Korean army's aging UH-1 Huey fleet. Korea Aerospace Industries has partnered with Eurocopter to develop the helicopter. They plan to build 245 helicopters, and Smiths intends to begin delivering its system for installation in 2010. While HUMS undeniably provides worthy data to enhance the safety and reliability of helicopter operations, the challenge can be to sufficiently analyze, and exploit, the data. "You can have huge amounts of data, but unless you extract the information and do something with it, it does little good," says Ephraim. Smiths, therefore, has been working with Agusta Westland to provide a Web-based data analysis service to AW-139 operators. Smiths hosts a server that takes in data, "and the operator gets a report back overnight," he adds. "The CAA determined 10 years ago that HUMS is 70 percent effective in detecting faults from a safety standpoint," says Ephraim. "But if you add analysis, it gets us up to 85 percent."

HUMS Maintenance Cost Benefits*

  • Reduced dedicated maintenance,
  • Improved maintenance scheduling and logistic support,
  • Reduced parts usage through accurate and automated usage monitoring,
  • Reduced no-fault-found (NFF) events,
  • Reduced consequential damage through early diagnosis, and
  • Improved event/incident/mishap analysis.
* Source: Smiths Aerospace

 

Composite Structure Monitoring
Aircraft manufacturers are incorporating more and more composite materials into their new aircraft structures. Airbus' giant A380 is made of 25 percent composite materials, while about 50 percent of the weight of the Boeing 787 Dreamliner is composite, a dramatic increase over the approximate 12 percent used for B777. Carbon fiber reinforced composite structures are lighter than metal structures and considered equally durable. But they still can show wear, often in the form of cracks or delaminations, which are many times not visible to the naked eye. Airbus, therefore, approached Japan's Research & Develoment Institute of Metal and Composites for Future Industries (RIMCOF) for assistance in developing structural health monitoring (SHM) technology. An agreement was made in mid July to jointly conduct a study, with "the intent of introducing SHM on next-generation commercial aircraft worldwide," according to an Airbus official. Established in 1981, RIMCOF is a public corporation primarily funded by the Agency of Industrial Science and Technology, part of Japan's Ministry of International Trade and Industry. RIMCOF member companies-Mitsubishi Heavy Industries, Kawasaki Heavy Industries and Fuji Heavy Industries-and Airbus have titled their joint project "The Japan Airbus SHM Technology for Aircraft Composite." A project team has been formed that will study the technology for five years, until 2010. In addition to evaluating SHM technology, they will conduct composite component tests and attempt to adapt the technology for use in aerospace. "No specific components are targeted [for testing] at this point," says the Airbus official. "The first step is to build components, and after the completion of certain milestones, flight testing can be envisaged." SHM technology is meant to immediately detect faults or abnormal transformations caused in the aircraft structure during flight. If it can be practically applied, its benefits are obvious: increased safety and reliability, and more efficient aircraft maintenance. The technology being studied detects invisible strain or cracks through light-conducting fiber that is used as sensors embedded in, or bonded on, the aircraft's composite structure. Airbus officials equate SHM technology to the human nervous system, in which the brain senses pain or uneasiness in the body. When fractures, cracks or delaminations occur, they destroy the fibers and thus interrupt the light flow. This interruption, in turn, allows the anomaly to be isolated. Other companies and research firms are evaluating technology comparable to SHM. The challenges, says one industry official, are whether it can be adopted on a large scale without being cost prohibitive, whether the embedded optical fiber adds weight and whether the fiber could compromise the composite material itself. Other structural monitoring technologies are being viewed, as well, including the use of acoustic sensors attached to a structure's surface. It applies the premise that as a crack propagates in composite materials it releases acoustic energy. "These technologies are still unproven," says an official. "There's the question of the practicality of taking them from the lab, where it might work once, to the aircraft, where it must continue working through its [aircraft's] lifespan-and also that the technology be 'manufacturable.'"

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