The commercial pilot ran out of gas and safely landed his open-cockpit experimental airplane in a field. He obtained 4.5 gallons of fuel and noted that the field grass was low-to-mid ankle high and relatively thin, which would lengthen his take-off distance. During the take-off roll, at approximately 40 miles per hour, the left main landing gear wheel struck uneven terrain and sheered it off, which caused the left main landing gear strut to dig into the ground and flip the airplane over. As a result, the vertical fin and the engine mounts were substantially damaged. The gear failed at a flat weld that attached a metal plate to the landing gear through the brake assembly. It could not be determined when the weld had been done.