Visualize a 44-ft-long and 15-ft-high aircraft with a 116-ft wing span and a gross takeoff weight of 25,600 lb. The plane takes off automatically and climbs to 65,000 ft where it travels for 42 non-stop hours across 14,000 nautical miles. Meet the Global Hawk, the future of unmanned reconnaissance spy vehicles.
The Northrop Grumman Ryan Aeronautical Center, the same company that built Lindbergh's Spirit of St. Louis some 70 years ago, is building the aircraft for the U.S. Air Force. It will provide field commanders with high-resolution surveillance images in near real time via satellite.
Beyond meeting stringent performance requirements, design engineers had to over- come major challenges:
A $10-million unit fly-away price requirement
A thirteen month time limit to provide an airframe for systems testing
Required integration of the aircraft's complex surfaces, structures, and subsystem designs
Given these challenges and timetable, Ryan replaced a second-generation wireframe CAD system with Pro/ENGINEER mechanical design automation software from Parametric Technology Corp. (Waltham, MA). Using this system, the Ryan Aeronautical Center facilitated a concurrent engineering strategy and implemented Integrated Product Teams (IPTs). And, they completed design without a hard prototype.
Ryan estimates that Pro/ ENGINEER, in conjunction with the IPT program, helped cut development time in half. In the future, the company plans to further expedite production by capitalizing on the system's manufacturing simulation capabilities to generate manufacturing process plans, tools programs, and time/cost estimates.
Enhancing team strategies. IPTs were a key focus of the company's concurrent engineering effort. All IPT groups work from a common budget split by product rather than department. For instance, the Global Hawk project included airframe, avionics, software, payloads, ground segment, and systems integration teams, among others. Subteams within the air- frame IPT consisted of several major disciplines, including designers, manufacturing engineers, stress analysts, tooling personnel, and other specialists.
Ryan Aeronautical Center Vice President Claude Hashem, who is in charge of the Global Hawk program, notes that the level of dedication Ryan invested in the IPT strategy helped create a new aircraft and engineering culture, one where communication is key and core design requirements systematically guide product detail development. The Global Hawk was the Center's first project in which electronic models were gospel, rather than drawings. And, as Hashem points out, because all IPTs had common access to the established design specifications and evolving electronic models, they were able to go back and confirm that each product iteration continually met larger design goals.
"Pro/ENGINEER's ability to allow teams to communicate instantly, on-screen, through electronic mock-ups made it the cornerstone of our communication process and aided our ability to always stay focused on our design requirements," explains Ramirez. "We still printed out drawings, but when we had a question, the electronic model was the law."
Electronic modeling. Members of the IPT teams used Pro/ENGINEER to design the Global Hawk's structures and harness and cable routing, as well as its fuel, environmental, bleed-air, and hydraulics subsystems. This capability allowed the Ryan Center to launch a concurrent engineering design process built around electronic models. After the teams established initial product design requirements and produced a basic structure of the overall aircraft, they established a manufacturing flowchart of "boxes" representing the various subassemblies and sub- systems. This chart became the bible of the Global Hawk's development allowing the team(s) to establish schedules and metrics for tracking each subassembly or subsystem. All engineers working on this product could access and review this file, perform final analysis, and make comments.
A product data package was then released, including all the assembly's related electronic files, drawings, work instructions, documentation, and any other extraneous files. IPT teams collaboratively reviewed this information.
According to Ramirez, Pro/ ENGINEER's parametric nature made interference checking between IPTs simpler because changes to one part or subsystem would automatically update any related components. The system's associative capabilities ensured that changes made in any stage of the design process would be propagated throughout all the models.
"Traditionally, for a metallic structure such as our fuselage, there would be four or five engineering change orders (ECOs) per drawing. For the Global Hawk, we averaged about one ECO per drawing," says Ramirez.
He explains, "We used the Pro/ENGINEER models as a virtual mock-up," he says. "We never did a physical prototype. We relied solely on the electronic definition. The sub- systems groups called up the structural assemblies as they were being developed and started evaluating their component installation in relation to the overall structure of the aircraft. The system pointed out interference problems between the subsystems and the structure, so the teams were able to develop solutions very quickly."
However, he emphasizes that Ryan Aeronautics Center relied on the entire concurrent engineering organization, not just the system's electronic modeling capabilities, to help pinpoint potential interferences. "In previous projects for a production prototype like this, various quality engineers and inspectors would participate," says Ramirez. "For the Global Hawk, we had just a final assembly inspector because team members themselves took responsibility for quality throughout the project."
Having a virtual mock-up of the assemblies on-line was instrumental in organizing sub- systems as well. Tubing and harnessing systems, for instance, were available in electronic model form, for all IPT members to see. "It really paid off," says Ramirez. "Everything fit together the way we expected."
Pro/ENGINEER helped IPTs rapidly create and route all the aircraft's plumbing subsystems, including the fuel, hydraulics, and bleed-air systems, so tubes don't obstruct components and technicians don't get any surprises during actual assembly. These subsystems, as well as the aircraft's power lines, intersect below the engine in a congested area known as the "hell hole"perhaps the UAVs most difficult interior location to design.
Design checks. Ryan used Pro/ENGINEER's surfacing capabilities to define all of the aircraft's complex external shapes, including the fuselage, radomes, wings, tails, nacelle, and inlet duct. Engineers used the aircraft shapes, after being evaluated for smoothness and continuity with Pro/ENGINEER surface analysis tools, to create wind tunnel models and perform CFD analyses at NASA Ames in order to verify the predicted aerodynamic characteristics. As these analyses were underway, the airframe IPT was already performing detail design of structural components defined by these surfaces. Under normal circumstances, final aerodynamic surfaces would be released prior to embarking on final detail design tracks.
Besides the "hell hole," interference checking was critical in other instances. The fuselage consists of approximately 950 sheet metal and machined parts. Less than 1% of those parts were scrapped due to engineering deficiencies. And those parts were often scrapped because they hadn't been checked for interference due to schedule constraints.
Pro/ENGINEER also allowed Ryan to exchange electronic models with subcontractors, such as Raytheon Systems Co., which designed the SAR electro-optical and infrared sensors payload subsystem using the same parametric software. Ryan also employed data from the system to demonstrate the UAV's performance for two customer presentations an animated film simulating the aircraft's ground and flight movement, and an Onyx graphics presentation that rotated the aircraft's assemblies across a rear projection screen 24-ft long and 6-ft high.
Flying forward. With two aircraft in operation and more than 20 sorties completed as part of its flight test program, the Global Hawk has started a series of 13 military exercise missions to demonstrate the utility, dependability, and flexibility of the unmanned aerial reconnaissance system before it goes into production. Two additional pre-production aircraft are nearing completion in the company's San Diego, CA plant.
Ramirez notes that Pro/ ENGINEER is one part of an ongoing commitment to concurrent engineering programs at Ryan. "Change is never easy," he says. "I lost a lot of sleep initially, knowing that we would be taking on the double challenge of implementing a new design system and designing a new airplane. But the paybacks were tremendous. We followed a plan and it worked."
What this means to you
Shorter design cycle by:
Operating in a fully associative structure
Eliminating the need for hard prototypes
Utilizing a concurrent engineering setting
Migrating from a second-generation wireframe CAD system to 3D software
The driving forces
Integrated sensor system. Consists of an all-weather Synthetic Aperture Radar/Moving Target Indicator (SAR/MTI), a high-resolution electro-optical digital camera, and a third-generation infrared sensor, all operating through a common signal processor. This system allows commanders on the ground to select radar, infrared, and visible wavelength modes as desired, and even use the SAR/MTI simultaneously with either of the other two sensors. The sensor system provides high-resolution image quality that makes it possible to distinguish vehicle, aircraft, and missile types, and to look through adverse weather, day or night. The system can search a 40,000-sq. nautical mile area in 24 hours with 3-ft resolution in the wide area search mode, or search 1,900 2-km-sq spots with 1-ft resolution.
Ground segment. Developed by Raytheon Systems Co. (Falls Church, VA), this system monitors Global Hawk and communicates reconnaissance data to ground forces. It consists of two elements, the Launch and Recovery Element (LRE) and the Mission Control Element (MCE). The LRE must be co-located with the aircraft at its operating base. The MCE, which communicates with the aircraft and the LRE through satellites, can be located anywhere in the world.
The LRE manages the take-offs and landings of the Global Hawk. It verifies the health and status of various subsystems aboard the vehicle, receives the mission plan from the Mission Control Element (MCE), and loads it into the aircraft. During launch and recovery, the LRE is responsible for air vehicle control, coordination with local and enroute traffic control facilities, and hand-off of aircraft control to the MCE once airborne.
The MCE provides management of the aircraft and its sensors. Four personnel in the MCE shelter operate the system's command and control, mission planning, imagery quality control, and communications functions. The MCE can manage up to three Global Hawks simultaneously; disseminating geographically dispersed, near-real-time information to tactical commanders.