WHEN the Boeing 787 airliner goes into commercial service next year, travelers will be transported on wings and fuselages made of advanced composite plastics. This raises a logical question: if modern plastics are sturdy enough for 600 mile-per-hour airplanes, why are car engines still made by pouring molten metal into molds, a 6,000-year-old process? That inequity is especially grating to Matti Holtzberg,…