Don't hold me to it but I think the SG managed to get into the air for at least a few seconds and a few feet.
Operational history
During a break in the Senate hearings, Hughes returned to California to run taxi tests on the H-4.[13] On November 2, 1947, the taxi tests began with Hughes at the controls. His crew included Dave Grant as copilot, two flight engineers, Don Smith and Joe Petrali, 16 mechanics, and two other flight crew. In addition, the H-4 carried seven invited guests from the press corps and an additional seven industry representatives. Thirty-six were on board.[19]
After the first two taxi runs, four reporters left to file stories, but the remaining press stayed for the final test run of the day.[20] After picking up speed on the channel facing Cabrillo Beach, the Hercules lifted off, remaining airborne at 70 ft (21 m) off the water at a speed of 135 miles per hour (217 km/h) for around a mile (1.6 km).[21] At this altitude, the aircraft still experienced ground effect.[22] The brief flight proved to detractors that Hughes’ (now unneeded) masterpiece was flight-worthy—thus vindicating the use of government funds.[23] However, the Spruce Goose never flew again. Its lifting capacity and ceiling were never tested. A full-time crew of 300 workers, all sworn to secrecy, maintained the aircraft in flying condition in a climate-controlled hangar. The company reduced the crew to 50 workers in 1962, and then disbanded it after Hughes’ death in 1976.[24]
Source: Wikipedia
Yes, it was probably due to a backfire. Millions down the drain. The Wright Brothers’ first plane flew longer and farther 40-50 years earlier.