The airplane landed with its right main landing gear partially at about 1130 Pacific time. The commercial pilot and flight examiner were not injured; the airplane sustained substantial damage. Visual conditions prevailed. When the pilot extended the landing gear, he did not receive a down-and-locked indication, observing the right landing gear was partially extended. After a series of troubleshooting steps, the pilot was unable to extend or retract the right landing gear. The pilot elected to land the airplane with the nose and left landing gear retracted. During the landing sequence the airplane sustained substantial damage to the lower fuselage structure.