Design News for Mechanical and Design Engineers

At 10 ft tall and 20 ft long, it probably wouldn't fit into your home office. If you did manage to put it there, its 20,000 lbs would fall straight through your floor into the basement. And at $1–5 million each, you most likely would not give one to your nephew for his birthday.

So what good is such a behemoth of a machine? When the U.S. military captures an enemy's missile, it doesn't destroy it. It brings it home "alive" into the lab, to see what it can do...and how U.S. airplanes can avoid it. And when companies like Boeing, Lockheed Martin, and Raytheon build missiles, they avoid crashing valuable prototypes after a single test flight by hooking it up to the machine.

"You can fly the missile against a [simulated] target that is performing evasive maneuvers," says Mark Avory, Carco's vice president of engineering. "The name of the game is to find out how complex maneuvers have to be in order to avoid intercept."

Carco's latest contract is to build a simulator for the U.S. Air Force, to develop the Kinetic Kill Vehicle Hardware-in-the-Loop Simulator (KHILS)—the most recent missile defense plan—at Eglin AFB (Fort Walton Beach, FL).

The new machine supplies five independent degrees of freedom: three axes control the attitude of the missile, and two axes control the target. Of course, computers must give the appearance of great distance—a live missile could fly hundreds of miles before reaching its target, but the Carco simulator holds them just 40-50 inches apart.

The machine is so advanced that the Department of State restricts Carco to selling the machine only to approved NATO countries and other U.S. allies. Most recently, India was dropped from the list because of its unauthorized nuclear weapons tests. Approved countries outside of NATO include Israel, Japan, South Korea, and Taiwan.

Carco makes just three new systems per year, Avory says. The 18-month design cycle begins as Carco engineers design a unique machine for a customer's demands, using Mechanical Desktop from Autodesk. But the machine's blueprints are so complex that it would take 30 minutes to model stresses and motion in FEA. So Carco engineers pare the CAD design down to its essentials, and run vibration, stress, and kinematic tests on each component with visualNastran Desktop (formerly Working Model), from MSC. Software. The motion simulation software allows Carco to demonstrate the machine to a customer before the year-and-a-half delivery time, and even to predict the gyroscopic torque effects of spinning the flight simulator through multiple axes.

To build the machine, Carco engineers construct all the moving parts from stiff, light magnesium, and the stationary parts from steel. Then they construct a 15,000-lb base to provide high inertia, and hook it all up to a 300- hp hydraulic power supply. This rotary actuator provides stepless switching with fast-acting servo valves, from Moog (East Aurora, NY). And they control the whole apparatus with 3200-Series floating point DSPs from Texas Instruments, which is enough computing power to provide servo updates 3,600 times per sec, at a pointing accuracy of±7 arcsec per axis.

Then, after the machine has passed all quality-control tests in the lab, engineers break the whole thing down and ship it to the customer. They rebuild and calibrate it on site.