On April 17, 2009, about 1240 mountain daylight time, an experimental amateur built Brinker / Garner tailwheel equipped bi-plane, N375CB, was substantially damaged during landing roll at the Caldwell Industrial Airport (EUL), Caldwell, Idaho. The airplane was registered to a private individual and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the test flight. The local flight originated from the Sunrise Skypark (ID40), Marsing, Idaho, at 1130. The pilot reported that during a routine test flight, he conducted a series of maneuvers to see how the airplane performed with full scale deflection of the control surfaces. Following the maneuvers, the pilot entered level flight and applied full throttle to perform a "top speed test." As the airplane accelerated past about 100 miles per hour, the airplane "started to vibrate severely." The pilot stated that after reducing the throttle and slowing the airplane down, the vibration lessoned around 70 miles per hour, and he decided to divert to EUL. The pilot entered the traffic pattern for runway 30 and proceeded to execute a wheel landing slightly left of the runway centerline. The pilot said that as the tailwheel settled onto the runway, the airplane immediately veered to the right. Despite the pilot's control and brake inputs, the airplane continued to veer to the right and exited the runway. Subsequently, the airplane came to rest in a nose low attitude adjacent to the runway surface. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the left and right wing assemblies and fuselage were structurally damaged. The left main landing gear wheel assembly was separated. The tailwheel remained attached to the airframe. The left and right springs remained attached and undamaged. Movement of the tailwheel by hand revealed that it locked into its normal turning radius and subsequently broke free with little pressure. No anomalies could be found, however, examination of the runway by the FAA inspector revealed a black rubber transfer mark with a width corresponding to the width of the airplane's tailwheel. The mark was not linear, but had a zigzag shape consistent with the tailwheel shimmying.