On August 20, 1998, at 1600 central daylight time, a Massey Christen Eagle II experimental homebuilt biplane, N72BJ, was substantially damaged after experiencing a structural failure while maneuvering near Galveston, Texas. The instrument rated commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered to and operated by the pilot. Visual meteorological conditions prevailed for the Title 14 CFR Part 91 local aerobatic flight for which a flight plan was not filed. The personal flight originated from Galveston's Scholes Field Airport at approximately 1545. The pilot reported to the FAA inspector that he was in the process of entering an FAA approved aerobatic box to practice maneuvers in preparation for an upcoming aerobatic meet. The pilot further stated that while in a shallow dive, at an airspeed of 190 to 200 mph, while at an altitude of 4,200 feet agl, he felt a flutter, accompanied by a severe airframe vibration. The pilot reported that he observed the flying wires on the biplane lose their tension "and make large loops." The pilot added that the airplane "may have rolled or tumbled;" however, he managed to regain control of the airplane after reducing the engine power and landed without further incident. Examination of the airplane by the pilot revealed that all four lower wing spars (forward and aft) failed in flight. In the recommendation block of the enclosed NTSB Form 6120.1/2, the pilot recommended a redesign of the drag and anti-drag blocks at the compression ribs. The reason for the failure of the lower wing spars could not be conclusively determined. The 1987 model airplane was purchased by the pilot on August 25, 1997. The airplane had accumulated a total of 607 flight hours. The last condition inspection was completed on January 20, 1998, approximately 83.8 flight hours prior to the accident. The pilot had accumulated a total of 936 flight hours, with a total of 125 hours in the accident make and model aircraft.