July 2, 2018

Engineers at Arnold AFB develop projectile telemetry capability to study boundary layer transition

Deidre Ortiz
Arnold AFB, Tenn.

Engineers with the Space and Missiles Combined Test Force at Arnold Air Force Base are developing a telemetry package that will be used to transmit data when launching projectiles at over 25,000 Gs. To accommodate a stand-alone electronics package, an antenna with a detachable radome and multiple integrated sensors, the projectile itself is made up of different parts and materials. Shown are the various parts of the project and then the projectile when totally assembled.

Engineers with the Space and Missiles Combined Test Force at Arnold Air Force Base, Tenn., are developing a telemetry capability that will be used to gather, transmit and record data when launching projectiles at over 25,000 Gs and more than 13,000 miles per hour.

Elvis Encalada, electrical engineer at Arnold, commented that the use of telemetry arose from the need to study boundary layer transition. Projectiles experience BLT, the transition from laminar to turbulent flow, when traveling at very high speeds. The specific location along the projectile body where BLT occurs is a critical parameter that effects the flight dynamics of the projectile.

“The main idea is to have the instrumentation and electronics inside the launched projectile,” he said. “The electronics will collect the BLT data and wirelessly transmit the data. Reception antennas will be placed along the range and used to collect the transmitted data which then goes to an RF (radio frequency) receiver, and ultimately, a computer.”

In addition to Encalada, Jesse Labello, Air Force project manager, and David Woods, mechanical engineer, have contributed to this effort.

Woods led the team in designing the modular projectile, which, according to Labello, was no easy feat due to the specifications required.

“The projectile has multiple components and is made of multiple materials,” he said. “It had to accommodate a stand-alone electronics package, an antenna with a detachable radome made out of a material that had not been used in G-Range before, and multiple integrated sensors – all in such a way that it can withstand the extreme pressures of the light gas in the barrel and G-forces upon acceleration and still function and fly. Suffice to say that if David’s design doesn’t work, the telemetry won’t work.”

During the developmental phase of the telemetry system, the three engineers partnered with the Army Research Lab (ARL).

“ARL specializes in small, high G-force, telemetry applications and played an integral role in our telemetry effort,” Encalada said. “ARL led the design for the transmitting antenna and the telemetry electronics we currently are using.”

He added ARL assisted in the process of properly integrating the electronics and mechanical bodies.

“The AEDC electronics collects instrumentation data and passes the digital data on to the telemetry electronics and transmitting antenna,” Encalada explained. “The projectile body was designed to enclose all of the electronics and the instruments used.”

To get an even better understanding and to see the telemetry package in action, Encalada took a trip to Aberdeen Proving Grounds. APG, which is located in Aberdeen, Maryland, conducts various kinds of military equipment development and tests which include weapons, ammunitions, artillery and vehicles.

“This is where the branch of ARL we worked with is located,” he said. “During my visit to APG, I witnessed the integration of AEDC electronics with ARL telemetry electronics, the process of potting the overall electronics into the electronics housing unit, and the survivability test of the electronics in a high G-force environment.”

While here, Encalada said he saw how vital potting the electronics inside the mechanical housing is in the electronics surviving the high G-force environments.

“Without proper potting, the electronics or crucial connection points would be damaged or crushed under its own weight when experiencing high G-forces,” he said. “G-forces would render the electronics/telemetry useless.”

After potting was completed at APG, the team traveled to the Adelphi Laboratory Center in Maryland.

“The ALC has an air gun facility which operates similar to G-Range, except on a much smaller scale and shorter time periods,” Enalada said. “Using the air gun, we were able to determine that the electronics can survive up to 23,000 Gs.”

Testing of the telemetry package in Range G at Arnold is anticipated to take place sometime next year.

“We hope that the end result will be that AEDC test customers will receive critical data about boundary layer transition during hypersonic flight and hypervelocity impacts that were previously unable to be measured,” Encalada said.

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