Tustin, CA--The ability to use stereolithography models of an impeller design in both wind tunnel and flight tests helped engineers at Southwest Aerospace (Tustin, CA) evaluate multiple variations of the impeller design in less time. Though the final component will probably be made of metal, the stereolithography versions proved strong enough to survive the tests and provide engineers with valuable data.
The impeller is part of the Special Material Kinetic Decoy (SMKD), a defensive tool the military is evaluating for use by aircraft to confuse heat seeking missiles. The decoy contains a special granulated material that ignites when exposed to air, and when deployed it's hoped that a hostile missile will home in on this burning material and not the aircraft's engines.
Inside the SMKD a gear train drives a plunger that pushes the flammable material from the decoy in a controlled fashion. The 1.9-inch-diameter, four-bladed impeller mounts to the front of the 7.5-inch-long decoy. Free stream air turns the impeller to provide power to the gear train.
To evaluate a variety of impeller designs, project manager Dave Smith turned to Solid Concepts (Valencia, CA) to create stereolithography (STL) models that could be tested in the wind tunnel. "This is unique in that the STL part is a flight part and not just for visualization," he says, "which is what most people use stereolithography for." The performance requirement is fairly high--the impeller might spin as fast as 25,000 rpm when placed in the wind tunnel at 400 knots--and it's impressive that an STL part could even do the job.
Designing an impeller of this size isn't easy, notes Smith, because analytical computer tools don't give very accurate results at this scale. His mission was to create an impeller that generated the required starting torque, power, and rpm necessary to expel the flammable material at a specified rate. He contracted with Solid Concepts to produce four different STLs each with slight changes to optimize performance.
Southwest Aerospace will produce 40 test models for its customer. Since 40 stereolithography models would be prohibitively expensive, Smith plans to use just a few STLs to produce investment castings for the impellers.