Shop personnel assist PWT in completion of blade spacer testing
By Bradley Hicks, AEDC/PA
/ Published May 08, 2018
ARNOLD AIR FORCE BASE, Tenn. -- When engineers at Propulsion Wind Tunnel 16T needed assistance on a recent test, personnel at the Arnold Air Force Base Model and Machine Shop quickly responded by lending equipment and expertise to ensure the test was completed on time and at a nominal expense.
The Flight Systems Combined Test Force at Arnold AFB recently awarded a contract for new C-1 compressor blades for 16T.
Christopher Gernaat, Technical Procurement and Structural Analysis engineer for the Flight Systems CTF, describes the C-1 compressor as “the heart of 16T” because it is responsible for moving air through the tunnel during operation and creating the airflow to simulate flight conditions.
The vendors designing the new compressor blades requested that the Flight Systems CTF provide them deflection data on the compressor blade spacers. These spacers prevent the compressor blades from over-rotating during operation. The spacers are designed for the 5,000-pound side load, and the vendors were interested in how the spacers would deflect under load.
“To date, the current spacers had not been tested for deflection, and the vendors wished to have test data on the parts as opposed to just analysis,” Gernaat said.
With little time and money to finish the testing sought, Flight CTF engineers and blade shop personnel went to work. They planned to test the spacers using a rig designed in the 1980s and built to be installed on a large tensile test machine at the Chem Lab. The test would have allowed the spacer to be pulled, simulating centrifugal force as well as applying side load.
However, this effort would hit a roadblock, as necessary equipment was missing from the box containing the testing rig.
“When the box was delivered from the warehouse, a large percentage of the parts were missing which made the original installation impossible,” Gernaat said.
Despite this, the engineers and blade shop personnel were determined to see the test completed. They decided to use the parts that were available and attempted to recreate the test at the Chem Lab by adapting a simplified fixture meant for side loading to the tensile test machine. But the group found that they could not safely mount the load fixture to the tensile test machine with the equipment on hand.
“Unfortunately, the base of the tensile machine was slanted and did not have sufficient space for large, high-strength clamps which were needed to hold the fixture,” Gernaat said.
This led 16T engineers to reach out to personnel at the Model and Machine Shop for advice. They first contacted Planning Supervisor Brad Reid, who in turn promptly asked machinists Bruce Prater, Joe Syler and David Taylor to assess the situation.
Together they determined to use the Shop’s 70-ton press to complete the test. They quickly helped engineers and those in the blade shop move the fixture from the Chem Lab to the Model and Machine Shop, found high-strength clamps necessary for safety during the test and mounted the spacers to the flat-based press.
“The press looked like a much more viable option, so the guys helped us safely transport and install the heavy fixture and then went to find large clamps to hold it in place,” Gernaat said. “They came back and installed the clamps for us. All of this happened in the span of approximately an hour right before the end of their shift.”
Engineers planned to apply only 5,000 pounds of force to the spacers. The 70-ton press has a load gauge attached, but the load engineers wished to apply was so small compared to the press capacity that the gauge would hardly register before the spacer was overloaded.
The following morning, machinist Dusty Rogers evaluated the setup and came up with a 10,000 pound-force portable hydraulic jack. This jack contained a gauge that could accurately display the 1,000 pounds of force increments engineers wished to record.
Gernaat said the testing was completed before lunch that day, something that would not have been possible without the help of the Model and Machine Shop.
“The only cost I know of was a few man hours for the shop folks, which was extremely inexpensive in schedule and cost compared to fabricating parts to adapt the fixture to the tensile machine,” he said.
More importantly, the craftsmen offered a simpler, safer solution than
the original loading rig that could not be duplicated, Gernaat added.
“The use of the 70-ton press allowed us to utilize the equipment in the manner which it was meant to be used as opposed to attempting to adapt a piece of equipment on the fly,” he said. “The press capacity was far in excess of the loads we intended to apply. In addition, the press was equipped with a metal mesh screen to protect us as we loaded the spacer in case an unexpected failure occurred.”
Gernaat said the help offered by those at the Model and Machine Shop was not surprising as he has always gotten great assistance from personnel there, but he said the extra mile that the Shop personnel went to ensure the test was completed quickly is greatly appreciated.
“The attitude of the shop personnel in jumping to help us on a project which was not originally in their scope of work for the day and taking the time to suggest a safe and simple solution was very much appreciated,” Gernaat said. “I am certain that we would not have finished the testing in such a short time, and perhaps not at all, without their assistance.”