On May 26, 2002, approximately 1500 Pacific daylight time, an experimental Hanson RANS S6ES airplane, N654RH, impacted the terrain during an attempted forced landing about one-half mile from Spanaway Airport, Spanaway, Washington. The private pilot, who was the sole occupant, received serious injuries, and the aircraft, which is owned and operated by a friend of the pilot, sustained substantial damage. The local 14 CFR, Part 91 pleasure flight, which was being operated in visual meteorological conditions, departed Spanaway Airport less than one minute prior to the accident. No flight plan had been filed. There was no report of an ELT activation. According to the owner of the aircraft, this was the third time the aircraft had flown since he completed its construction. On the second flight, there was an unexpected interruption of power during the climb out, and the owner had since sought advice from the manufacturer of the airframe kit and the company that built the engine. After taking the actions recommended by those parties, the owner performed an on-ground engine test run while varying the aircraft's pitch attitude from that of level flight to maximum climb. After the test run was completed with no apparent problems, the pilot took off in order to evaluate the performance of the engine while airborne. Although the aircraft accelerated and climbed out to about 400 feet without any apparent performance degradation, it soon thereafter began to lose engine power. The pilot therefore immediately turned back toward the airport, but was unable to reach the runway before descending into a nearby residential area. Because there was no suitable landing area, the pilot attempted to land on the street, but collided with trees and a parked vehicle. Although it was the opinion of the owner that for an undetermined reason fuel flow to the cylinders had been interrupted, the reason for the power loss was not able to be determined.