AEDC completes longest engine test in its history

  • Published
  • By Deidre Ortiz
  • AEDC/PA
ARNOLD AIR FORCE BASE, TENN. --  For the first time, an accelerated mission test (AMT) was accomplished for the F101-GE-102 engine in the Aeropropulsion Systems Test Facility (ASTF) altitude cell C-1 at Arnold Engineering Development Complex (AEDC).

The $21 million test program was the longest single entry of a jet engine in AEDC's history. The engine ran more than 2,145 hours and completed 1,504 missions.

The AMT conducted on the F101, which is used in the B-1 Lancer, was highly successful, demonstrating a 4,000 Total Accumulated Cycle (TAC) life for the engine core. 

AMTs simulate the wear and tear of an engine over a given period of time based on historical data from the field along with the environmental conditions that the aircraft are flying in. For example, aircraft flying in Alaska will be exposed to different life-limiting conditions than an aircraft flying in the Middle East.

"The 11-month, 4,000 TAC AMT equates to about 10 years or approximately 4,700 flight hours of actual engine usage," said Mike Dent, lead engineer of the AEDC Aeropropulsion Test Branch.

Because they're meant to affirm durability and life limits during the development and operational use of jet engines, AEDC project manager Josh Hartman explained that AMTs simulate flight hours at an accelerated rate.

"This is why 2,145 test hours equates to about 4,700 flight hours," he said. "The primary purpose of this 'accelerated pace' is to save on test costs and schedule."

He added the engine goes through a series of thermal cycles to simulate the Low Cycle Fatigue (LCF) that the engine would experience in the actual field.

"The cyclic behavior is the 'damaging' portion of the engine running and is therefore the most important part of the AMT mission," Hartman said.

The F101 engine test was accomplished in C-1, which is not a typical test site for an AMT. The test cell was used while the Complex's primary sea level test cells were occupied by F135, F119 and F100 engines for the F-35, F-22, and F-16 fighter jets. 

Hartman stated that the AMT was also unique in other ways, aside from being completed in an altitude cell. For example, before the 12-month period required for the test program, the test cell underwent extensive modifications to the Exhaust Gas Management System (EGMS) bulkhead on its aft end, as well as cell cooling air modifications.

"The largest requirement was for a diffuser to be installed that allows for the plume from the engine to pump down the test cell to draw in cooling airflow without the need to run any plant machinery for sea-level testing, which significantly saves on test costs," Hartman said. "The atmospheric intake was successfully used in C-1 for the first time, allowing for a path for the engines inlet air without running plant airside machines."

Initially, acoustical issues created higher than desired vibrations that caused a delay in the start of the test.

Acoustics can be damaging to the test cell infrastructure, as well as the test article. Therefore, Hartman along with the test team and General Electric used an experimental approach to solving the problem.

"Plume penetration water sprays were added to get cell acoustics down to an acceptable level by injecting water directly into the engine plume to drive down the acoustical energy by flashing the water into steam, using the high latent heat of vaporization of the water," Hartman said.

The vibration problems and late delivery of the engine set the program behind schedule. To assist in getting back on schedule, 24-hour operations, four days per week were initiated in November 2013.

A portion of the AMT required hot summertime temperatures to achieve engine inlet temperature requirements. Unfortunately, summer 2014 in southern middle Tennessee was not as hot as previous summers. This meant that AEDC had to generate the heated air, which comes at an undesirable expense. 

Had the test been accomplished in the Complex's sea level cells, a much more affordable heated inlet capability would have been available. Luckily, with the help of a Jacobs Engineering Research Grant, a plan was devised to minimize plant costs.

"The mass flow of the F101 requires two 27,000 horsepower compressors," Dent said. "A 'hybrid' concept was tested and implemented that required only one compressor with the balance of the air mass requirement being supplied through an atmospheric inlet hatch."

This process also allowed the test to continue running 24 hours by using the heated inlet at night when temperatures are lower and sea level operation during the day for inlet conditions that didn't require the hot inlet temperature. Cost savings were approximately $380,000.

"The test ran 24-hour operations, four to six days per week, to finish in time to prepare for a high priority test with a firm start date in C-1," Dent said. "AEDC's operating contractor did a tremendous job integrating all the plant, test cell, maintenance and utility requirements to make this a success."