The Arnold Engineering Development Center at Arnold Air Force Base, Tenn., s the site of choice for a unique engine test currently underway in the Complex’s Sea Level 1 (SL-1) test cell.
The Pratt & Whitney Canada PT6A-68 turboprop undergoing testing at AEDC powers the Texan II that is used by the U.S. Air Force for basic pilot training and the U.S. Navy for primary and intermediate joint Naval Flight Officer and Air Force combat systems officer training.
When asked why the Air Force Life Cycle Management Center’s Propulsion Directorate decided to bring the PT6A-68 turboprop engine to AEDC for a nine to 10 month Accelerated Mission Testing (AMT), Hugo Heyns, Air Force Life Cycle Management Center’s Propulsion Directorate, Propulsion Acquisition Division PT6 Integrated Product Team lead, said the answer is simple.
“The PT6 Integrated Product Team, in concert with the JPATS System Program Director, determined that an AMT would provide an early understanding of engine failures allowing time to address them before they affect the fleet, thereby assuring continued success of the PT6 engine,” he said. “Further, that the program would be better served with an AMT conducted by an accurate and objective test facility with extensive aircraft engine testing experience. The U.S. Air Force’s AEDC clearly fits that description.”
This is the first time a T-6 Texan II engine has undergone an Accelerated Mission Test (AMT) at AEDC’s SL-1 test cell. The test represents a number of other firsts, including the first use of a propeller for loading the engine.
“This test is the first project where ATA has been contracted to provide maintenance and inspection services in addition to the installation and operation of the engine and support systems,” said Brian Knack, a turbine engine project manager with AEDC’s Aeropropulsion Branch. “We’re also doing a dynamic analysis on the rear of the engine – the auxiliary gear box. We’re trying to define the vibration modes at the rear of the engine where some parts have been failing in the field. Even though the engine is lightly instrumented, we will be measuring a number of performance parameters, including vibration, fuel flow, airflow and trending engine speeds.
“We’ll be relying on the engine parameters that are within the engine control that we’re going to be reading in addition to some test cell measurements that we’ll be making.”
Further, Knack said “This test is an endurance test on the PT6A-68 engine. It’s an overhauled engine – it’s not a new engine. We’re evaluating the durability of the engine through its second overhaul interval. We’ll be putting a whole overhaul interval’s worth of test life on this engine during this test.”
Lt. Sam Stephens, AEDC’s project manager over the test, said, “Primarily, we’re continuing this pacer engine’s life at an expedited rate. This engine is going to have about twice the [flight] hours as any other PT6 in the T-6 trainer fleet. Maintenance and durability is our primary concern [with this engine].”
During the nine to 10 months of testing, the PT6A-68 will be subjected to the number of Total Accumulated Cycles an engine would experience in flight between depot overhaul periods. TAC is a unit of measurement for major rotating engine components tracked during an engine’s operational life.
Heyns said, “The PT6 AMT is intended to provide visibility into the future of the Joint Primary Aircraft Trainer System program engine fleet, identifying and defining issues of concern which may have impact on the fleet in sufficient time to take preventative and/or corrective actions before actual impact to the fleet’s availability.”
The PT6 engine is a derivative of a commercial engine with significant operational history in a wide variety of applications – the engine was selected, in part, because of this history.
Considering the JPATS mission is somewhat different than many of the engines other applications, initial engine modifications were used to address them.
Heyns said, “For example, the JPATS need for inverted flight demanded oil systems modifications to assure continued oil flow during inverted flight. Program engineers have also identified possible sources of future failures – and will use the AMT to study them in more detail.”