For unmanned vehicles that achieve hypersonic speeds, the performance of the combustion engine is paramount. Ball bearings play a pivotal role in the fuel delivery system. After calculating the basic rating life – the total number of revolutions before the first evidence of material fatigue occurs – Engineers select bearings that will meet the design or desired life. The life of a bearing under actual operating conditions before it fails or needs to be replaced for whatever reason is the bearing service life. And if that service, or useful, life precedes the desired time of operation for the vehicle, prohibiting it from reaching its destination, the dreaded MF occurs: mission failure.
For a manufacturer of the propulsion system (jet engines) for these unmanned, hypersonic vehicles, which travel more than five times the speed of sound, optimization is key. That means every facet of operations — every material, working condition, and controllable variable — must be optimized in order to achieve, and sustain hypersonic speeds where air molecules actually separate and high-temperature effects stress the vehicle and it’s sub-systems.
“Anything that is mission-critical has to be 100% reliable,” explained Steven Sanchez, Engineering Manager at AST Bearings. “The ability to accomplish the mission safely must be achievable and repeatable.”
In its initial design of the engine, the manufacturer encountered a performance weakness: the bearing configurations selected yielded at most 30 seconds of vehicle life before experiencing a catastrophic failure (in some cases, bearing failure was almost immediate). Bearing failure at these high speeds results in fractured components and flying debris damaging other components, such as the turbine, and in turn, lead to complete engine failure.
The manufacturer sought a more durable bearing configuration beyond the standard product offering, one that would allow their vehicle to operate for longer. The manufacturer reached out to AST to find a solution.
AST engineers accepted the challenge, assuring the manufacturer that it could improve the bearing life significantly, targeting a factor of 10, a projection that, if achieved, would significantly expand the capability of the end user’s vehicle.
“In the world of extreme,” said Sanchez, “it’s tweaking and optimizing that gets you across the finish line. You need a bearing expert who knows what to tweak and has the tools to determine and validate those optimizations.”
Find out how AST engineers helped this manufacturer of liquid fuel pumps and gas compressors prevent mission failure in Mission Critical Success – Part 2. Coming February 21, 2020.