Usually, when Pratt & Whitney designs a new jet turbine it begins with a list of 700 to 1,200 requirements. These will instruct engineers on all aspects of the powerplant, including what type of ball bearings to use, how to rig the lubrication system, and detail temperature tolerances in different parts. The requirements are born out of decades of experience with building such systems and are like a rigid best practices checklist.
But for the company's latest 700lb (3.12kN)-thrust engine, it threw all but three of those requirements out of the window. Tasked by the US Department of Defense to innovate faster, better and cheaper, P&W's GatorWorks prototyping arm based in West Palm Beach, Florida, gave a small team of about 15 hand-picked employees a narrower focus.
"I literally gave them three requirements for the project, which were: it had to be 700lb of thrust; it had to meet the air force's target, which they told us was $100,000 cost; and it had to fit in the envelope of that existing size of engine," says David Stagney, senior director at GatorWorks. "And that was it. We let the team go off."
The result is a new engine core that was designed, built and tested in less than a year, he says. "We actually went from the [physically based rendering] to fabricating the entire engine and the test stand in five months."
Limited requirements had other benefits beyond speed, he adds.
"Because they weren't overly constrained by a very large number of requirements, they came up with a bunch of really innovative ideas, including the fact that this new core has multiple applications in potentially other vehicles, including subsonic and supersonic versions," Stagney says. "And also, [they] came up with something that is at least 10% more fuel efficient, and at least 30% cheaper than what we think is out there today."
The new 700lb-thrust-class engine is a clean-sheet design that borrows some core technologies from P&W's TJ-150 turbine, used in Raytheon's Miniature Air-Launched Decoy (below). However, this latest engine is designed for use on next-generation cruise missiles or tactical unmanned air vehicles (UAVs).
P&W declines to say specifically what product it is intended to power, although its low cost makes it "attritable", in military speak. The engine developer says its design should have a service life of about 20 missions.
Stagney says the engine core is a "minimally viable product”: a term borrowed from the world of Silicon Valley start-ups. Such a class of products are ordinarily rough-and-ready creations designed to give a customer something to look at, test and to give feedback on.
GatorWorks is taking a page out of the playbook of digital start-ups by developing its products iteratively, as part of a back-and-forth conversation with the US military services. The company declines to disclose its possible customers for the 700lb-thrust-class turbine, but says the potential clients were pleased.
"We brought a bunch of customers here, [and] we showed it to them," Stagney says. "Having an actual engine with real performance in that short time period allowed us to collaborate with our customers. And they actually wanted something a little bit different. We were able to incorporate that into our second iteration of the project."
After seeing the first iteration, the US military customer was willing to trade a 10-15% increase in cost for slightly more fuel efficiency, to enable greater range performance, says P&W.
GatorWorks plans to incorporate those new requirements into its next year-long iteration of development. After a third one-year-long phase, the company hopes to win a contract to go into production. It believes it could manufacture up to 1,000 examples of the engine per year.
The P&W unit has about a dozen projects under way, about half of which are new or derivative engine development efforts, says Stagney. The rest are fresh technology development initiatives. GatorWorks has about 200 people working at its prototyping centre. Its activities are conducted using a roughly equal split of internal and external funding.
Demand for faster and cheaper engine development is a result of a US Air Force vision of fleets of low-cost missiles and attritable UAVs that can overwhelm, dodge or outdistance Chinese and Russian air defence systems. The expanded capability of such equipment over recent years has caused US military commanders increasing anxiety because of their growing sophistication and extended range performance.
The US Air Force Research Laboratory plans to invest up to $725 million in jet turbine research and development between fiscal years 2018 and 2026, through its Advanced Turbine Technologies for Affordable Mission programme.
Requirements include reduced maintenance, greater thrust and better fuel economy – advances that should combine to facilitate an increase of 60-70% in stand-off range performance.
KEEP IT SIMPLE
GatorWorks says its one-year, short sprint approach has a number of advantages over a traditional process where it would build one new engine model every 15 or 20 years, such as the F135 turbofan powering Lockheed Martin's F-35. In the past, that long development cycle sometimes caused personnel to over-engineer their one small part of the project, which ultimately was a distraction from the most important areas of engine performance.
US Air Force
"Because we're only gearing one new engine every 15 or 20 years, every engineer takes that opportunity to try to put in every possible technology – like this is [their] shot to put it in and get their technology to fly," says Stagney. "If we're doing a new engine every single year, and we're planning to do multiple upgrades and multiple iterations of that engine, then we just need to solve today's problem today."
In fact, the iterative process is being helped along with advances in technology, in particular 3D printing, which allows P&W's engineers to quickly build and test their ideas, he says. In one such case, the company took a section of another undisclosed, in-development engine – including the combustor, feedings of the fuel system and housing – that was previously 99 separate parts and 3D printed it as one part in less than 24h, saving machining and hand assembly time.
"The designer designed the part, designed the tool and printed the tooling overnight and we had the part on the machine the next day. That's truly an enabler for our kind of rapid prototyping," says Stagney. "It's a significant saving in terms of the cost and lead-time development, because a lot of parts of the engine have significant lead-time for tooling, test equipment, fixtures and inspection."
The ability to 3D print structures also allows P&W to have free-flowing conversations with its customers, Stagney notes.
"So, we showed our customer, 'Hey, we can actually 3D print this portion of the engine. And, this is going to allow us to now incorporate maybe different types of heat exchange, allow it to adapt and to fit into different vehicles,'" he says.
P&W believes it can always refine its design and add more requirements later.
"It's always easier to add performance, add complexity and add costs, rather than what we typically do, which is to try to go for the highest-performance design and then try to take out the cost," says Stagney.
Correction: The article was changed after incorrectly naming the TJ-150 as the PJ-150.