Robert L. Hall, 85, an aviation pioneer who designed jets for Grumman Aircraft Engineering Corp. after getting his start creating Gee Bee racers, died Sunday in Springfield, Mass. The revolutionary Gee Bee Model Z racer, the "City of Springfield," powered by the first of Pratt & Whitney's high-horsepower radial engines, took the Thompson Trophy after winning every event in the 1931 National Air Races.