Wings Magazine

Successful test for LORD’s propeller balancing system

Oct. 6, 2011, Cary, N.C. - LORD Corporation has completed extensive testing of pre-production hardware of their In-Flight Propeller Balancing System as part of a $4.5-million contract with the U.S. Air Force (USAF). 

October 6, 2011  By Carey Fredericks

The testing, which was the second development test and evaluation (DT&E) of the technology, was completed and has transitioned into a year-long operational test and evaluation (OT&E). This testing is part of a System Design and Development (SDD) contract received from the USAF for the integration of LORD Corporation's proprietary In-Flight Propeller Balancing System (IPBS) into the USAF's C-130H fleet equipped with 54H60 propellers. The contract from the 330th Aircraft Sustainment Group (ASG) of the Warner Robins Air Logistic Center (WR-ALC), Robins Air Force Base, Ga., was awarded in late 2008 and spans until December of this year. Consisting of a funded $2.7MM base effort and three unfunded options totaling $1.8MM, the contract includes extensive flight and user acceptance testing for their 500-plus C-130 fleet. 

Proven Technology
Although this technology is new to the aerospace industry, LORD Corporation's balancing technology has been in service in extremely harsh conditions in industrial applications for almost a decade. It has logged millions of service hours in applications ranging from turbo-compressors to large extraction fans and high-speed machining spindles.

Traditional means of dynamically balancing propellers — adding counterweights — allows for proper balance at one specific operating condition and for a limited amount of time since the propeller blade angle and aerodynamic loads change during flight. The negative effects of propeller imbalance vary from passenger discomfort to fatigue of on-board equipment. The effects of wear on the system also degrade balance over time. Further, significant costs are expended keeping vibration under control or simply monitoring its effects so as to predict potential failures. In comparison, the IPBS continuously adjusts balance during flight operation. The result is propeller balance maintained at the lowest possible level during the entire flight and reduced Direct Operating Costs (DOCs).

The system is comprised of one balancing device per propeller and a single controller per aircraft. The computer-controlled system uses accelerometer inputs from the rotating propeller to automatically adjust the balance as needed to minimize total system imbalance for each operating condition.  In addition to managing the IPBS system, the small electronic controller also can serve as a predictive maintenance tool.


According to Justin P. Manna, Business Development Manager for LORD Corporation, "Controlling vibration with on-line, fully automated balancing technology will lead to reduced maintenance workload and will increase durability and lower the cost of operations. This benefits the USAF by reducing maintenance workload, improving aircraft readiness and improving the reliability of engine-mounted components on C-130 aircraft."

Proof in the Numbers
The testing process actually began several years ago. A four-hour flight test was conducted in 2004 with sponsorship and oversight from the USAF Air Mobility Battlelab and engineering support from the Robins Air Force Base C-130 System Program Office (330th ASG). The demonstration began with the installation of an IPBS on a 54H60-91 Hamilton Sundstrand propeller system. Several typical flight profiles were conducted with the support of the 339th Flight Test Squadron of Warner Robins Air Force Base, Ga.  Although vibration levels varied throughout the power spectrum on the 54H60-91 propeller, once activated, the IPBS proved it could maintain vibration levels at approximately 10 to 20 times less than any condition between thrust reverse (-6,000 inches-pounds torque) and maximum power (18,600- inches-pounds torque). Throughout this operating range, the required balance corrections varied in both amplitude and in angular position. In addition, the performance of the IPBS was unaffected by ambient air temperature from ground to 20,000-feet. The data gathered demonstrated that the IPBS is capable of performing required corrections automatically and reliably, with no additional workload for the flight crew.

In 2009, LORD Corporation flight tested the system on four propellers at Kirtland AFB.  The system performed at expected control levels throughout the flight profile and vibration on all four engines was reduced to < 0.05 inches per second during all flight conditions. Overall, the tests showed a 94 percent reduction in propeller vibration levels and 75 percent reduction in propeller induced vibration measured at the compressor. Manna noted that the 2009 test validated that the technology.

According to Manna, the 2009 and 2011 tests both demonstrated that the EM-IPBS concept is a robust in-flight system for turboprop aircraft that should produce significant operations and support savings, realized by eliminating the lengthy maintenance actions required to periodically balance propellers per the requirements. "The reduced maintenance also will increase readiness by returning aircraft to the operational squadron earlier. Further, the large reduction in propeller vibration should provide a significant decrease in the maintenance cost of engine, gearbox and airframe mounted equipment."

The high level of predictive maintenance afforded by IPBS also can be used to provide Prognostic Health Management (PHM) and diagnostics information to maintenance crews, said Manna. Since the system results in less fatigue for both on-engine and on-board equipment, as well as lower failure rates, DOCs are reduced.  In fact, Manna estimates that the IPBS will save the USAF approximately $340 million over the life of the system.

"The IPBS has been proven to provide the smoothest and most reliable propeller operation across the entire power spectrum," said Kris Burson, LORD Corporation Americas Marketing Manager,  Aerospace & Defense. "In addition to lowering operating and sustainment costs, the system will reduce aircraft downtime due to maintenance and therefore increase aircraft availability."

Funding for this testing contract ($2 million) was sponsored by U.S. Senators Arlen Specter (R-PA) and Robert P. Casey, Jr. (D-PA).  In a press release announcing the funding, Senator Specter said, "I am pleased that my colleagues have recognized the valuable contribution these projects will make to our nation's defense. Pennsylvania is a top competitor for defense projects that create jobs and strengthen our economy and these funds will go far in supporting the brave men and women who serve our country."

"The projects will play an important role in strengthening our nation's military readiness and promoting job creation in Pennsylvania," said Senator Casey. "I am pleased that my colleagues have approved this important funding to improve Pennsylvania's military installations and strengthen our nation's defense."


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