Case Studies: A 49,000-Pound Challenge
Niacc-Avitech Technologies (Fresno, CA) is a Federal Aviation Authority and Joint Aviation Authorities (FAA/JAA) certified repair station. During its 25 years in business it has developed a number of compliant repair and overhaul capabilities for regional and commercial aircraft. The company services electrical/electronic, fuel, hydraulic and mechanical aircraft appliances and components.
Niacc recently received a customer request to add overhaul capabilities for landing gear shock absorbers for Embraer EMB-145 aircraft to its portfolio of services.
Explains Rayan Kabeer, Niacc head of engineering and product development, “We told them we would look at it. We reviewed the component maintenance manual and determined the acceptance test specifications.”
One of the requirements was the verification of a load vs. position specification that would require Niacc to purchase new test equipment. Kabeer sought equipment that could perform compression, extension and cyclic tests on the shock absorbers at 49,000 pounds.
Extensive Testing ProcedureSome shock absorbers, depending on whether they are in for a scheduled overhaul or for an unscheduled failure, are tested as they are received. The parts then go through disassembly, assembly, inspection and final acceptance as specified in the component maintenance manual. All shock absorbers are tested before they leave the Niacc facility.
The first test is the proof-pressure test, in which the shock absorber is mounted on the test set and deflected to a certain length. Then the shock absorber is charged with hydraulic fluid and is inspected for failure. After that, a charge of nitrogen is added and the shock absorber is put on the stand again; it is cycled six times with both the nitrogen and hydraulic charges to see if there is any external leakage.
Lastly, there is a final functional test, in which the shock absorber is put back on the test set and monitored for any obvious pressure drops; it is compressed to a certain deflection and the load is checked to make sure it falls within a graphing limit provided by the manufacturer.
The Right Test EquipmentKabeer researched some specialized test equipment suppliers but found that the equipment ranges were either too high or too low.
“The load issue was one of the real challenges,” says Kabeer. “For this type of shock absorber we were looking into 49,000 pounds. Everything the other company had was too big or too small. They could have custom made it, but it would have taken a tremendous amount of time.” Niacc would also have had to buy separate linear variable displacement transducers LVDTs, which would add cost and complexity.
Kabeer found Admet (Norwood, MA) on the Internet and then called the company. “We talked with Admet about load and pressure and what the requirements were,” says Kabeer. “We gave them all the parameters that we needed and there was a lot of back and forth.”
Admet specified an ExPress 60,000-pound, dual-column servo-hydraulic materials testing machine with a top mounted actuator, as specified in the component maintenance manual. Admet also recommended the MTESTWindows materials testing system, Microsoft Windows-based software that controls tests, collects and reports data, and offers tabular and graphical representations of test results for analysis and comparison.
Test Control, Analysis, ReportingThe unit arrived within six weeks. Niacc handled the setup and then called in a calibrator. Kabeer installed the software on an existing computer that is now dedicated to the process.
“We just had to hook the machine up with our computer and then load the software,” says Kabeer. “We installed the load cell ourselves. It was pretty much plug and play.”
Kabeer especially likes MTESTWindows, because with the software Niacc can control the test practically without operator intervention. The software also graphically plots the test results and highlights any test parameters that are out of tolerance to facilitate the identification of failures.
The results are saved in a database that, according to regulation, is kept for two years after the part has been shipped.
With the Admet equipment, Niacc was able to respond to its customer’s request for a new line of testing and is now providing the service to other customers that operate EMB-145s.
Incremental business is possible because the Bombardier CRJ-200 aircraft uses the same type of shock absorber and, with a 60,000-pound capacity, the ExPress can be used to test larger shock absorber assemblies.