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Wheels-up! The retractable landing gear that is now commonplace on commercial and military aircraft was first developed for Glen Curtiss’ Triad airplane in 1911. This aircraft was amphibious, so the retractable wheels were used to help the Triad take-off or land on water. By the 1930s, landing gear was being developed for other aircraft models, bringing with it an increase in speed and efficiency.
An airplane’s landing gear is a compromise between how it handles on the ground, and other factors that impact how a plane handles in the sky, like weight, performance, and reliability.
The Douglas SBD-6 Dauntless—an aircraft that helped the United States win the Battle of Midway during World War II—uses inward-retracting gear. The struts on the landing gear fold in, bringing the wheels horizontally into the fuselage.
Inward-retracting gear like this allows for a wide stance on the ground, which makes for a more stable take-off and landing. But, it also impacts the weight and maneuverability of the aircraft. The way that this type of gear is configured puts more weight further out on the wing, which affects how the aircraft handles in the air, and is a consideration in pulling off aerobatic maneuvers. Though the Dauntless' wings don't fold, many naval aircraft's wings do, and engineers must take this into account when placing the retractable wheels.
Inward and outward retracting gear (like the kind pictured here on the Dauntless) provides a flat stowage of the wheel, eliminating the need for deep wheel wells or complicated folding mechanisms. In the case of the Dauntless, the aircraft’s engineers decided to compromise on streamlining and save weight by leaving the wheels themselves exposed when raised, but with faired-over hubs and a close fit to the wing to minimize drag. This improves the speed and range of the aircraft. In the case of the Dauntless, the retractable gear also made the airplane more stable in a diving attack.
Looking closely at this photograph, you can see the solid, metal areas at the center of the wheels. Those are the faired-over hubs, attached to the wheels by three screws, which you can see near the outer edge of the covers.
Aside from helping with a stable take-off and landing, the retractable gear served another important purpose on the Dauntless. The wide stance of the gear on the ground also made it easier for armorers to attach bombs to the aircraft—in this case, a single bomb would have been in the narrow space, seen at the center of the photograph between the main gear wheels.