The planned Wasp-Major powered bomber, the B-29D, was to incorporate considerable changes in addition to the engine installation tested in the XB-44. The use of a new alloy of aluminum, 75-S rather than the existing 24ST, gave a wing that was both stronger and lighter, while the undercarriage was strengthened to allow the aircraft to operate at weights of up to greater than the B-29. A larger vertical fin and rudder (which could fold to allow the aircraft to fit into existing hangars) and enlarged flaps were provided to deal with the increased engine power and weight, respectively.