Designers Go Digital
Terry Costlow

New capabilities in design and simulation are influencing many aspects of aerospace product development.

Computers have brought numerous benefits to design engineers, automating a number of tasks and making it far easier to reuse technologies. But the advances have come with a downside - the engineers have to turn out more complex designs in shorter time periods.

PCs and workstations have transformed the design process over the past decade or so as designers have shifted entirely to digital design. Design, simulation, and verification help meet the compressed development cycle requirements while also trimming costs by reducing the need for building prototypes.

Another aspect of the shift to digital technologies is that as communications improve, there is more competition in global markets. That feature is making it mandatory for aircraft designers to make sure that all aspects of their designs move quickly from the initial drawings to a plan that is ready to move into manufacturing.

"During conceptual design, there’s only a short time to look at candidate designs and alternatives," said Mark Beyer, Senior Engineering Specialist, Research and Advanced Technology at Cessna Aircraft. "We've got dozens of engineering disciplines, and we need to consider different aspects like damage tolerance, strength, aerodynamics, and especially weight."

Cessna is tackling this aspect of the design with an internally developed program called MassMorph. It takes the many elements of previous designs and converts them into mass properties that fit within the concept craft. These mass properties include the specifications for subsystems and components for planes that have already been through the design process.

While many parameters will change for the new design, there will be a number of aspects that will change only slightly if at all. Now that the company has been using digital-design techniques for years, there are a number of completed subsystems ready for reuse.

"We can leverage the modules we’ve invested tens of thousands of hours in, morphing them into credible models for the concept design. That lets us examine the full complexity of the design, which has hundreds of thousands of parts in as many as 18 levels," Beyer said.

The software works even if the concept takes some dramatic steps from previous designs. "Even if we go to something radically different, we can still borrow 80% of the design from our legacy aircraft," Beyer said.

Managing these complexities is one of the biggest challenges facing design engineers and those who create software for them. While airplane manufacturers write some of their own software, they also use a number of off-the-shelf packages.

In the past, those programs usually addressed only one aspect of a design, such as electronics or hydraulics. But as computing power has increased, desktop computers can now let engineers see how the various aspects of a design work together.

"It's mandatory to analyze multi-domain simulations, looking at electronics, mechanics, hydraulics, thermals, and structural elements together," said Paul Latiolais, Saber Product Marketing Manager at Synopsys.

Planes like Cessna's Mustang are designed with a range of software tools.

This simulation capability is becoming more critical as aircraft manufacturers rely more on their suppliers to give them completed systems. While that approach speeds up design and lowers costs, it can be more difficult for the aircraft makers to link together products they didn’t design from scratch.

"Typically, the OEM is a system integrator that’s got a few models to simulate. By running them together, they can see the impact of each component on the robustness of the complete system. They can spot instantaneously problems that were kind of difficult to see with old-fashioned engineering techniques," said Nils Johnson, Corporate Application Engineer, Saber, at Synopsys.

Moving quickly
Among their many benefits, multi-level simulation and hardware-software verification shorten develop time. That is particularly true with Cessna's MassMorph, since engineers do not have to redesign components that have already been modeled. "This is at least an order of magnitude faster," Beyer said.

He adds that there aren't any of the sacrifices that might come with using elements designed for a different aircraft. "We don’t just morph; we can optimize the designs for the new configuration," Beyer said.

To help airframe designers further reduce their development time, software developers are coming up with new techniques to speed processing. Designers today can run simulations on their personal desktop computers, but the huge size of aircraft simulations means these runs must often be done overnight or at least over lunch breaks.

But the move to distribute tasks to run on several different computers is already underway.

Along with its MassMorph program, Cessna designs with Dassault’s CATIA.

"Our newest software provides distributed computing; farming simulations that sometimes include thousands of elements out over a network instead of using only one PC. The engineer can farm out a Monte Carlo statistical analysis or a variable analysis," said Mike Jensen, Synopsys' Technical Marketing Engineer for Saber.

More software is being used on today’s aircraft.

While digital-design technology is moving to a distributed model, some of the actual software that runs on planes is moving the other way. Many aircraft engineers are leveraging the power of new processors, which are fast enough to run multiple programs at the same time, to reduce the number of control modules on a plane. That is changing the way software is written.

"Vendors are putting multiple applications on one computer to save space and make the planes lighter. When you do that, you've got to protect one program from another, so if one system goes down it doesn't impact the other. We’re offering a partitioned operating system that makes sure there's no impact from that, and also giving each application a certain amount of time so a rogue program can’t take control of the system," said Greg Gicca, Marketing Director, Safety Critical Products at Green Hills Software.

Many levels
While engineers are moving to more complex, full-system simulations, there is a similar effort in the lower-level products as well. For example, electronic subsystems are becoming more complex, so these designs must go through multiple simulations before the designs move forward to the complete system. The ever-growing complexity of large microprocessors is posing challenges for tool developers. "Designers now are using a lot of embedded software and they're using chips that have five million gates, a five times growth over just three years ago. With that size chips and complex real-time software, the verification process is a major challenge," said Lauro Rizzatti, General Manager of Emulation and Verification Engineering’s U.S. operation in San Jose.

The need for specialized tools poses another challenge for those involved in the digital design chain. There are not many popular standards in the development tools world; so many companies still use proprietary interfaces. That can make it difficult to move from one design platform to another.

Linked together
One way around the multiple-interface problem is to minimize the number of software families that are used for the main applications. Software providers generally make it simple to move a design along when various aspects are all done with their software.

"We've consolidated on one CAD system, so compatibility is not as big an issue at Cessna as it is at some other airframe companies," Beyer said. Cessna uses software from Dassault Systèmes, which makes CATIA and other packages.

Even so, it is not possible to do everything with that line, so Beyer would like to see more compatibility with the other tools Cessna designers’ use. "One thing we'd like to see more of is interoperability- having an open framework with open access to the geometries. A lot of tools have proprietary interfaces that only the companies that design them have access to," he said.

This incompatibility has not been lost on entrepreneurs who look for market openings. At least one startup aims to help engineers go from the earliest stages of a design to the setup for manufacturing.

"There are trade-offs. Engineers want a language that’s human-understandable, but the problem is to get that down to something that runs efficiently. Engineers often start in Matlab [from The MathWorks] to get the math correct. We can go directly from Matlab to implementation," said Randy Allen, CEO at Catalytic, a startup that makes development software.

Once designs get to manufacturing, the push for more compatibility continues. Design for manufacturability is a key part of many new designs.

But there is still a fair amount of disconnect between development and prototyping software and the programs that drive machines on the factory floor. Many companies are working to make this aspect of design and production more seamless. For example, Siemens upgraded its software late in the summer, making sure its numeric control software is in close relation to the equipment it drives.

"What happens in the numeric control kernel is exactly what happens on our 840D. There's no guessing. You know exactly how the part will come out because the output of the kernel goes directly to program the 840D," said Tim Shafer, Director of Siemens Aerospace Center of Competence.