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
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
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.
Tweet This
2 
