Using modern, high-fidelity computer software, U.S. Army engineers are solving issues that crashed earlier attempts at leap-ahead helicopter technologies, an approach service officials say should shave time, risk and cost from the effort to field a revolutionary rotorcraft.
The Army has not had a successful new-start rotorcraft development program in almost half a century, Dan Bailey, the Army’s director of Future Vertical Lift, said Aug. 23.
RAH-66 Comanche reconnaissance helicopter
“When you think about it, it’s been decades since we’ve had … next-generation rotorcraft,” Bailey said at the Army Science and Technology Symposium hosted by the National Defense Industrial Association in Washington, D.C. “The fixed-wing fighter community has moved forward. They’ve got fifth-, now sixth-generation fighters out there working development efforts. We are still in the second and third generation in terms of rotorcraft.”
The newest rotorcraft to enter U.S. military service — the V-22 Osprey — was designed “when the supercomputers of the day were less powerful than the phones that are in our pockets today,” said Andrew Wissink, an aerospace engineer with the Army Aviation Development Directorate. “As a result, they depended heavily on very primitive computational models and a lot of scale-model testing.”
Many of the problems that plagued the V-22 in flight test and early operational history were caused by inaccuracies in modeling and simulation during development, Wissink said. The same goes for the RAH-66 Comanche stealth armed reconnaissance helicopter, he said. Both were initially designed in the 1980s and ‘90s with low-fidelity computer modeling.
Scale model testing works well for determining performance of isolated components — rotors, fuselage — but proved less accurate when those components were scaled up and tested in concert. Comanche worked well when scaled down, but the operational prototype had issues with the main rotors interacting with the fan tail, which required a total redesign 17 years into the program, he said.
“If you’re having to redesign that far into the program, by that point it is very hard to get back on track,” he said.
When the first operational V-22 Osprey was built, engineers relied heavily on scale models to understand how a full-size aircraft would perform. When the first Osprey was built and tested, they found it had 20 percent less hover performance than expected, he said.
“Once you have that kind of issue to deal with, everything else in the design … you have to compensate,” he said. “That’s one of the reasons these programs have had a lot of issues.”
High-fidelity modeling software like the Army Aviation and Missile Research Development and Engineering Center’s Helios code is becoming vogue in aircraft development, and is in regular use in the Army’s Joint Multi-role Technology Demonstration (JMR-TD) program. Helios is one of several programs aimed at developing software to better model aircraft performance in simulation before bending metal.
“I think with some of the tools available to us today, we could have identified some of these issues that dogged these earlier programs,” he said.
In earlier development programs, high-performance computing and high-fidelity modeling were used to address problems discovered during flight testing, Wissink said.
“What we’ve been trying, in recent years, under the JMR-TD program, is to move that use of high-performance computing and high-fidelity simulation further to the left with the intent of influencing the design earlier … at a time where it has an impact on cost,” he said.
Companies involved in the Joint Multirole Technology Demonstration (JMR-TD) program are using Helios and several other government and proprietary modeling software, he said. Boeing, Sikorsky and Bell are using Helios; they have to have a license to use it for their own commercial purposes, but can use it at will for government applications. Karem uses an in-house tool.
“Helios is becoming the preferred code to use only because the DOD supported its development and the Army uses it … and provided it to U.S. manufacturers,” Wissink said. “These vehicles — at smaller scales they perform a certain way and then if you scale up, some of the performance, weight becomes an issue and so forth. That’s where the high-fidelity tools can really pay off because we have the ability to scale within the computer by basically just modifying our input files.”