The fixed undercarriages caused a major fraction of the drag of sleek fibreglass airframes. All undercarriages were enclosed with fairings and doors when retracted. They also featured refinements such as retractable undercarriages, fully enclosed cockpits, and low-drag, all-metal wings. The main and nose undercarriages were housed entirely within the fuselage. In 1926 Bradford Kendall began to manufacture railway couplers and undercarriages. Drag has also been minimized by more aerodynamic shapes and retractable undercarriages. Osgood also built road-ready mobile units that used Mack truck undercarriages. Faster aircraft have retractable undercarriages, which fold away during flight to reduce drag. Radius rods are also sometimes used in aircraft with fixed (non retractable) undercarriages. As per October 2007, ICAO revised the alpha factor for four wheel undercarriages. For the 1984 year only, all of the tractors came with black frames and undercarriages. All of the aircraft were damaged, with some having their undercarriages shot away. One of the mobile home undercarriages was tossed at least . It was packed, with people even clinging to the roofs and undercarriages. Problems with the Brigand became apparent during operations in Malaya, with undercarriages failing to lower.