APL engineers use plastic to build new test missiles

Innovation saves time, cuts cost of production

January 22, 2001|By TaNoah Morgan | TaNoah Morgan,SUN STAFF

Two aeronautical engineers at the Johns Hopkins Applied Physics Laboratory in Laurel say they've found a way to build better missiles, save taxpayer dollars and bring new business to the lab in one simple idea: use plastic.

As part of an independent research project, Richard R. Heisler and Clifford L. Ratliff designed a way to make plastic models for use in wind tunnel tests that keep their integrity, provide quality data during the tests and shave tens of thousands of dollars off the cost of a typical wind tunnel experiment, as well as months of time.

The models have proven to work well in Mach 1 (the speed of sound) conditions. They will be tested in the next few months under two to five times the wind pressure of Mach 1.

If all goes well, the lab may have a product that creates more cost-effective opportunities for defense agencies and contractors, and one that will help keep them from making costly mistakes.

"This machine and these materials are possibly the next step" in missile design, said Heisler, a section supervisor in APL's applied aerodynamics department.

Traditional wind tunnel models are made from steel, aluminum or other metals that can withstand high winds without compromising stability tests. While the metal models have given excellent results for decades, the cost to create the models is prohibitive to small companies that lack funding and large ones that want to experiment.

One metal model can cost between $100,000 and $150,000 to manufacture, and a model is typically used in one test that can cost up to $2,400 an hour. And if the wind tunnel test disproves analytical data that said the missile would fly, companies must incur the costs again to cast a new model and retest it.

"You don't want to commit those kinds of resources unless you know this is the model that's going to [be developed]," said Ratliff, a senior analyst with the applied aerodynamics department.

Heisler and Ratliff cast a plastic model for testing last year for $40,000, and the readings from wind tunnel tests were similar to results obtained from tests of a $130,000 metal model of the same design. The engineers think plastic models will be able to help designers know early in the process what works and what doesn't.

"The key was we were able to obtain data comparable to an all-metal model," Heisler said. "We feel we can obtain high-fidelity data" from the plastic model.

The idea of using plastic was simple enough, and it has been used by auto manufacturers for wind tunnel testing, but it had never been done successfully enough in tests that put the material through the speed-of-sound pressures that missiles withstand, Heisler said. The plastics would warp or break under the high winds. Heisler and Ratliff's success came from two ingredients. They used a very durable plastic -- like the kind used to make computer housings or golf clubs -- and they strengthened the model from the inside with a metal shaft onto which the plastic casings are attached.

They built and tested their model in August with $75,000 that the lab granted to support their research. Because the test was successful, they have applied for a patent on the design. They were awarded another $75,000 from the lab this year to study the models under more extreme conditions.

The Navy has seen how the plastic models work.

When the team working on the Tomahawk missile had questions about the amount of torque it takes to rotate the missile's fins in flight, they had less than two months to find the answers and not enough money in the budget or time to build the section of the model they needed in metal.

APL, which works closely with the Navy on a variety of projects including the Tomahawk, offered to build the section in plastic so that they could run tests. Heisler and Ratliff designed the piece in about half the time it would have taken for a metal model, and at a fraction of the cost.

"Preliminary analysis indicates the data is very positive," said Cathy Partusch, a Navy spokeswoman. "It was a very positive effort for the team."

The wind tunnel confirmed data that was different from the data the Navy contractor was using.

"They could've been going down the wrong avenue and sure enough, they'd be deploying off the ship and straight into the water," Ratliff said.

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