09/30/2008. Remarks by Ray Watkins: "The enlarged eight to ten seat model 48A YH-12B of the model 48 XR-12 had separate doors for the crew and the passengers. The three-wheel landing gear of the earlier model was replaced by a four-wheel system. Problems occurred with the rotor dynamics and Bell accepted assistance from the Wright Field Propeller Laboratory. The USAF considered that too much work was required to resolve the problem and opted for the Sikorsky S-51."