With a group of associates, including the American inventor and aviator Glenn Hammond Curtiss, Bell developed the aileron, a movable section of an airplane wing that controls roll. They also developed the tricycle landing gear, which first permitted takeoff and landing on a flying field. Applying the principles of aeronautics to marine propulsion, his group started work on hydrofoil boats, which travel above the water at high speeds. His final full-sized “hydrodrome,” developed in 1917, reached speeds in excess of 113 km/h (70 mph) and for many years was the fastest boat in the world.
Bell's continuing studies on the causes and heredity of deafness led to experiments in eugenics, including sheep breeding, and to his book Duration of Life and Conditions Associated with Longevity (1918). He died on August 2, 1922, at Baddeck, where the Canadian government maintains a museum containing many of his original inventions.